Immunology module 1

anti-vax movement

# Since 1808 (the first vaccination campaign) people have been associated with this movement. # Some people (who don't understand how they work) felt very afraid of the Cowpox vaccine # Some people feel it's an inappropriate intervention of the state over individual liberty. Correlation does not mean causation! # This was the problem with blaming vaccines for Autism. In fact, the starting age of autism is at the same time of the measles vaccination → only implies a temporal relation (no causation!)

type 1 diabetes mellitus

(AI) multisystem metabolic disease, due to impaired insulin production; There is no insulin production due to impaired beta pancreatic cells (were targeted by the immune system) * Peak onset is 11-12 yo * arterial atherosclerosis → ischemic necrosis of limbs & internal organs | microvascular obstruction → damage to retina, renal glomeruli, peripheral nerves * Pt. depends on insulin to live

Signaling pathway activated by FcεRI engagement

(At least 2 IgE needed) 1. Cross linking of allergen-IgE-FcεRI on mast cells → receptors brought closer together 2. Lyn tyrosine kinase phosphorylates nearby ITAMs 3. Syk recruits to ITAMs of the gamma chains → activated → phosphorylates the LAT adaptor protein 4. LAT becomes a docking site for: * PLCγ → which catalyzes PIP2 breakdown into:- DAG → activates PKC- & IP3 → which increases cytoplasmic [Ca2+] → activates PLA2 * Grb2/SOS - a GTP/GDC exchanger - activates Ras & other small G proteins (upstream of MAP kinases) → activation & translocation of TFs necessary for cytokine gene expression (late phase) + activation of PLA2 → phosphatidylcholine ⇒ arach. acid ⇒ PGD2 & LTC4 (lipid mediators) (int. phase) - Both the ↑ Ca2+ and PKC ultimately lead to degranulation (early phase)

How is the DNA cut out? (genetic isotype switching mechanisms)

(DNA loops) 1. DNA R-loop that is formed is fundamental, since it is single-stranded - meaning that the AID enzyme (Activation-Induced Deaminase) can work on it (it's part of a repair mechanism for ssDNA) → it converts Cytidine into Uridine by deamination → 2. Uridine is foreign to DNA and can't bind to the opposite strand so the cell tries to fix it: UNG enzymes(Uracil N-glycosylase) remove the Uridines ⇒ forming abasic sites → 3. Ape1 endonucleases cleave these site ⇒ forming nicks at each position * GC-rich switch region RNA (made from the other strand) is degraded by a protein complex (RNA exosome) - so that C residues are exposed transiently allowing AID, UNG, and Ape1 to generate nicks there too ⇒ forming double stranded breaks → the breaks on each side of the loop are joined together

B lymphocyte tolerance

(Same definition as in T cells) - Necessary for maintaining unresponsiveness to thymus-independent self antigens,such as polysaccharides and lipids. - Also plays a role in preventing antibody responses to protein antigens.

PHYSIOLOGIC EFFECTS induced by eukaryotic parasitic invasion

(after prototypic activation of EOSINOPHILIC CELLS) → also ultimately leads to type 2 inflammatory reactions But the mediators released after degranulation have a more powerful parasiticidal action [e.g. major basic protein (MBP) and eosinophil cationic protein]→ effects can also damage the host tissues, but generally these mediators and enzymes (e.g. eosinophil peroxidase) are released very close to the parasite to avoid this.

​ζ-chains

(homodimer) play pivotal role in intracellular assembly, surface expression, and signal transduction via the pre-TCR and TCR complexes.

Characteristics of allergens

(recognised as antigens by immune system) - Low molecular weight - Highly soluble - Stable - Contain peptides that can bind to MHC Class II (for T cell priming) - They're proteins B cells undergo isotype switching to form IgE. Only proteins can stimulate isotype switching. - Found in low doses - high doses can be tolerated

IgE

* Allergic reactions * 0.004%

Pathologies related to the complementary system

* C1, C2, C3, C4 → involved in removing antigen/antibody complexes → Lack of these proteins: ⇒ SLE - Systemic Lupus Erythematosus - >50% of C1q/C2/C4 deficiency develop it ⇒ Chronic renal disease ⇒ repeated infections * C5, C6, C7, C8 → Lack of these proteins ⇒ repeated Neisseria infections ⇒ higher risk of Gonorrhea / Meningitis * C9 deficiency → no problem! (Because C5, C6, C7, C8 can lyse the bacteria also alone)

Type II hypersensitivity

* IgG and IgM antibodies are directed against antigens on self (such as circulating red blood cells) or extracellular material (such as basement membrane). --> Activates complement system against self Symptoms appear within hours - Usually induces production of autoantibodies (i.e. attacks antigens on self-cells) - Cytotoxic mechanisms can cause direct and indirect tissue damage - Can cause abnormal phyiological responses w/o cell or tissue injury

Two methods of checking pre-existing alloantibodies (to check if translplant is possible)

* Make sure that there are no pre-existing alloantibodies. 1. Mixing recipient serum with WBCs from potential donors → to see if (and how much of) the donor cells are lysed by antibodies from the host's serum --> Attain Percentage % = Panel Reactive Antibodies (PRA). Low PRA = Tranplant possible 2. Microbeads covered with MHC repertoire (similar to the MHC molecules of the potential donors) → A fluorochrome called fluorescein isothiocyanate is added to detect binding - FITC-conjugated anti-Fc antibody:If IgG Abs against those MHC (microbeads) are present in the recipient serum - the FITC antibodies will bind to the IgG ABs of the recipient and fluorescent.

HLA typing

* PCR sequencing from both donor and recipient. - Usually genotyping of HLA-A, HLA-B, & HLA-DR are performed. Because: HLA-C is less heterogeneous (than HLA-A & B) HLA-DP (class II) is usually in equilibrium with HLA-DR (enough to know 1) HLA-DQ - no real well-known role - Graft survival after transplant is increased with lower number of mismatching MHC alleles (i.e. less mismatch = better)

Development of lymphocytes from the pluripotent stem cell

* Pluripotent stem cells give rise to distinct B and T lineages

Complement system inhibition; soluble inhibitors

* Regulating the pathways is important, since C3 can be spontaneously cleaved and trigger the pathway. 1. C1 inhibitor = a serine protease inhibitor (serpin) that mimics the normal substrates of C1r & C1s 2. Factor I = Factor I breaks down C4b or C3b into ic3b (i for inactivated) → it's a potent opsonin with no enzymatic activity → can't propagate the alternative pathway. - Factor H & C4bp = are cofactors of factor 1

Destruction of joints in rheumatoid arthritis

* Stimulation of osteclasts by T cells

PHYSIOLOGIC EFFECTS induced by allergic mediators

* Systemically anaphylaxis Vasodilation & Vascular leakage Mediator: mainly histamine via histaminergic receptors H1, H2, H3. Endothelial cells contract → ↑ of interendothelial gaps → ↑ permeability → leakageOn a systemic level → can lead to cardiovascular shock → Epinephrine needed urgently! Typical sign of vascular permeability & skin edema: wheal & flare Intestinal hypermotility (due to gut smooth muscle contraction) Bronchoconstriction Mediators: leukotrienes (most powerful) Tissue damage: Mast cell/basophil granulation → proteases released → destroy surrounding tissue + promoting fibrous remodelling Inflammation: Mediators: cytokines & lipid mediators that recruit & induce activation of more leukocytes (e.g. neutrophils, macrophages, eosinophils, basophils, Th2 cells) Feature of the late phase → forms enlarged inflammatory edema

Mature T lymphocytes

* The T cells has a TCR complex + coreceptor molecules (CD4 / CD8) - IgSF. Mature lymphocytes leave the primary lymphoid organs (BM / thymus) → reach peripheral lymphoid organs → resting state (NO proliferation, NO production of cytokines, NO cytotoxicity) until they meet their antigen and become activated.

Hapten-carrier effect

* The effect caused by the dependency of a carrier protein in order to elicit a immune response; without a carrier no response will occur. - Utilized in vaccinations in under 2yo since they can not use a thymus independent response = Conjugated vaccines. A hapten is a small molecule that can only be immunogenic (be recognized by a B cell and thus induce Ab production) if bound to a larger carrier protein. This is true because only if the hapten is bound to a bigger protein co-stimulation with T cells can occur.

Acute haemolytic transfusion reaction

* example of complement dependent type II hypersensitivity following transfusion of ABO incompatible blood--> preformed antibody (predominantly IgM) against donor red cell antigens not found in an individual of a particular blood group (e.g. anti-A IgM in an individual with blood group B), bind to the donor red cell surface and lead to rapid complement mediated haemolysis.

Prevention of Fetus Rejection by the Maternal Placenta; 3 mechamisms

* half of the MHC molecules (codominant) with her fetus (the others are inherited from the father) → should be recognized as non-self by the mother. 1. Placental trophoblasts don't express classical MHC molecules, but rather HLA-G, which are minimally polymorphic and can inhibit NKCs, since they're ligands for KIRs → NKCs don't attack the fetus 2. Uterine trophoblasts produce a lot of anti-inflammatory cytokines (TGF-β, IL-4, IL-10) → immune reaction inhibited → fetus antigens attacked only if they exit the uterus.The mother may produce Abs against paternal HLA molecules (like against RhD Ags), but these anti-HLA Abs are not dangerous in further pregnancies. 3. Low expression of MHC Class II molecules

Innate immunity against viruses

* inhibition of infection by type I interferons and NK cell-mediated killing of infected cells. * recognition of viral RNA and DNA by endosomal TLRs and activation of cytoplasmic RIG-like receptors and the STING pathway--> Converge on the activation of protein kinases, which in turn activate the IRF transcription factors that stimulate interferon gene transcription. * MHC1 expression is shut off --> NK cell kills

Membrane bound inhibitors of the complement system

*CR1 (CD35) = Induces inactivation of C3 convertase and targets factor 1 for cleavage of C3b & C4b → limiting the alternative pathway - DAF (Decay Accelerating Factor, CD55) = induces dissociation of C3 convertase components MCP (CD46) = cofactor for Factor I for cleavage of C3b & C4b Protectin (CD59) = Interferes with the assembly of the MAC by binding to C7 & C8

3 ways of complement protein activation

*Classical Pathway (CP)* AKA antibody-dependent pathway, since the connection between the complement proteins complexes and the pathogen/damaged cells is mediated by antibodies. *Lectin Binding Pathway (LP)* Antibody-independent (considered innate imm.) Similar to classical pathway, but with mediation of carbohydrates (mannose) on the pathogen surface *Alternative Pathway (AP)* Antibody-independent (considered innate imm.) A pathway that is always on, but at a slow rate, since it doesn't rely on antibodies/mannose-binding lectin protein to bind the pathogen/damaged cell. It is enhanced by PRoperdin on the pathogen's surface

Antibody structure

- 3 equal-sized globular portions joined at the hinged regions - 2 light, 2 heavy chain - Classification is done according to the Fc (5 types) - Flexible and can bind more than one antigens

Allergies epidemiology

- 30-40% of the Western World population has allergies (once considered atopic patients) - It's becoming more common because hygiene is ↑ (→ less exposure to bacterial and viral infections esp. during infancy → no tolerance and Th1 cell activation towards diff. antigens)Clean environment → induces activation of more Th2 cells (than Th1) and vice versa. - Rural env. have more allergens but also increased tolerance towards them.

CAR-T structure

- Extracellular →(Variable part) Vheavy+Vlight → linked by scFv - Transmembrane domain - Intracytoplasmic multiple domain → part of the TCR machinery with a Z chain and other co-stimulatory motifs to fully activate the T cell.

Heavy region classes

- IgD →membrane antibody; never soluble - IgE →monomer; allergies - IgA → (Mainly dimer) mostly mucous; breast milk - IgM →dimer or pentamer; connected by J chain. - IgG → 4 types; IgG1, IgG2, IgG3 and IgG4 most abundant.

Etymology of complement deficiencies

- Inherited (less common?): Autosomal recessive - Acquired: E.g. Severe infection / autoimmune condition → no more left! In Lupus → C3 & C4 get used up → deficiency

Which antigens are found in the thymus?

- Many circulating and cell-associated proteins that are widely distributed in tissues. - Many protein antigens that are expressed in different peripheral tissues, so that immature T cells specific for these antigens can be efficiently deleted from the developing T cell repertoire.

Germinal centre function

- Site of intense multiplication & Proliferation (from 1 B cell can go up to 5000) of B cells; These cells express Bcl-6 - Genetic diversification of activated B cells - Survival of the fittest cell

Factors affecting immune response to a specific antigen (7 factors)

- Specificity - Distinguishing immunogens from antigens - Amount - number of responding B cells, their rate of antibody synthesis, and the persistence of the antibody after production. - Persistence - in the plasma and extracellular fluid bathing the tissues; is determined mainly by its isotype. - Isotype - Each one has different half life that determines the biological effects. - Affinity- strength of binding of the antibody to its antigen in terms of a single antigen-binding site binding to a monovalent antigen - Avidity - total binding strength of a molecule with more than one binding site. IgM, for example, will have a very high avidity (See pic) - Folding - may hide an epitope, and therefore affect the immune response.

The complement system

- System of proteins that is complementary to the antibodies - Part of the innate immunity (bridge the innate & adaptive imm.) + inflammation - Produced in liver - Composed of > 50 circulating + membrane-bound proteins

inflamed tumor microenvironment; factors that stimulates tumour growth

- Th2 cells - secrete cytokines leading to differentiation of mø into M2 → promote rebuilding and reshaping of tissues, inc. angiogenesis (= advantageous for the tumor) - T-reg cells - release cytokines that inhibit Th1 & CTL (= against tumor destruction...) - Myeloid-derived suppressor cells - they also inhibit Th1 & CTL (= against tumor destruction...) - Innate immune cells - they generate free radicals → DNA damage → ↑ mutations in TSGs and oncogenes (= good for the tumor)

Neonatal Fc Receptor (FcRn)

- Transports antibodies from mother's circulation to fetus - Protects IgG from intracellular catabolism - increases half life - IgG taken up into endosome at acidic pH - IgG-_____ complex to recycling endosome and released at neutral pH --> back into circulation

Clinical synthesis of MoAbs

- murine antibodies are not in main use, eventually can be recognized as foreign bodies and be attacked by our immune system. - chimeric antibodies, where the Fc part was human (65%) and the rest animal - humanized, with only around 5% animal portion. However, can also induce HAHA (Human against human antibodies)

Adaptive immunity to viruses

-Antibodies block viral binding and enhance viral phagocytosis during extracellular stage of infection & CTc kill infected cells (can cause some tissue damage) * most effective antibodies are high-affinity antibodies produced in T-dependent germinal center reactions: Antibodies are effective only when the virus is extracellular.

6 possible mechanisms of cancer immunotherapy

1. (Vaccinations) Immunization of tumor-bearing individuals with tumour antigens = enhanced immune response against the tumour. 2. Blocking Inhibitory Pathways to Promote Tumor Immunity 3. Augmentation of Host Immunity to Tumors with Cytokines 4. Non-Specific Stimulation of the Immune System (local administration of inflammatory substances) 5. Adoptive Cellular Therapy [CAR-T]= transfer of cultured immune cells that have anti-tumor reactivity intoa tumor-bearing host 6. Anti-tumour antibodies = may eradicate tumors by the same effector mechanisms that are used to eliminate microbes 7. Transplantation of Hematopoietic Stem Cells (HSCs) 8. Retargeting oncolytic herpes viruses to specific cancer cells

3 scenarios in which the immune system can recognize cancer-derived antigens

1. A normally methylated (silenced) gene becomes demethylated due to the cancer → expressed ⇒ protein presented on MHC 1 → CTLs recognize the antigen and kill the cell 2. An oncogenic protein is overexpressed in a tumor cell → the single cell over-expresses and presents the same type of peptide → tolerance threshold hit → CTL response triggered 3. Cells that express a tissue-specific protein (e.g. tyrosinase) excessively proliferate due to cancer (e.g. melanoma) → many cells express this protein antigen → CTL immune response triggered

Peripheral tolerance of B cells (3 mechanisms)

1. Anergy & Deletion Some repeatedly-stimulated self-reactive B cells may become unresponsive. These cells require more-than-normal BAFF for survival. Since they can't compete with normal B cells → they are eliminated more rapidly (shorter life span) than non autoreactive B cells. 2. Signaling by inhibitory receptors Self-antigens only engage BCR (not also coreceptors, helper T cells etc. like protein antigens). Lack/defects in inhibitory proteins that continue the signaling of ITIMs on the cytoplasmic tail of CD22 leads to autoimmunity. 3. Downregulation of specific chemokine receptors This mechanism helps hinder the return of the B cells into the lymph nodes, so that they don't proliferate & differentiate into plasma cells; A mechanism unique to B cells.

Peripheral tolerance mechanisms

1. Anergy (unresponsiveness) - Two mechanisms lead to it - Lack of co-stimulation by APC; Presence of inhibitory receptors 2. Suppression - Regulatory T cells: can recognize self-antigens → induce production of immunomodulatory cytokines → they turn off the immune response & block T cell activation 2. Deletion - T cells with a high-affinity to self-antigens / or that are repeatedly stimulated by the same antigen (implying this antigen may be a self-molecule) → die by apoptosis

Pathogenesis of SLE

1. Apoptosis + B&T to self (genetic + external triggers) → apoptosis to a certain degree + defective clearance of apoptotic bodies → burden of nuclear antigens + T & B cells create Abs against the apoptotic components → ++ ICs formed 2. The ICs may be engulfed by circulating plasmacytoid dendritic cells (Recognised as DAMPS) which form many type 1 interferons (IFN-α​ & ​IFN-β​) to sustain the production of antibodies → more ICs created (a vicious cycle)

General Features of Autoimmune Disorders

1. Autoimmune diseases may be either systemic or organ specific, depending on the distribution of the auto antigens that are recognized; e.g., diabetes 1 is organ specific. 2. Various effector mechanisms are responsible for tissue injury in different autoimmune diseases: include immune complexes, circulatingautoantibodies, and autoreactive T lymphocytes 3. Autoimmune diseases tend to be chronic, progressive,and self-perpetuating: self antigens that trigger these reactions are persistent, and once an immune responsestarts, many amplification mechanisms are activated

Causes for hypersensitivity diseases

1. Autoimmunity: reactions against self antigens 2. Reactions against microbes; in the reaction is excessive or microbes are very persistent --> Severe inflammation 3. Reactions against environmental antigens; 20% of individuals produce IgE that causes allergy. * Mechanisms are the same as normal elimination of diseases, but Immune response is not controlled properly.

Classification of GVHD

1. By severity from 1 to 4 2. Acute and Chronic

Cancer vs. immune system; 2 mice experiments

1. Cancer is targeted by the immune system - See pic. Basically removing and implementing a tumor in a different body area of the same mouse leads to rejection of the cancer growth 2. in-vivo, immune cells are seen infiltrating tumor growth → the higher the CD3 (T cell) infiltration is = the better the survival 3. Cancer growth directly related to the immune system: - From a nude (immunosuppressed) mouse → cancer rejection Because the tumour cells haven't had to deal with the immune system of the original mouse - haven't developed any mechanisms to evade/against the IS - From a normal (immunocompetent) mouse - no cancer rejection

Therapeutic strategies against asthma [5 methods]

1. Chromons (Cromolyn) → Inhibitors of degranulations; act on the cytoskeleton of mast. 2. Cysteinyl leukotrienes antagonists (Pranlukast, Montelukast, Zafirlukast) → Prevention of production/effect of lipid mediators (leukotrienes, prostaglandins) so you worsen the situation but eventually block the arachidonic acid effect. *NSAIDs should not be used because they inhibit cyclooxygenase - not lipoxygenase (which produce leukotrienes leading to bronchial constriction) 3. Albuterol → Salbutamol (Ventolin) → β2 adrenergic receptor agonists - to stimulate bronchodilation in the lungs caused by β2 adrenoceptors 4. Corticosteroids → Blockage of cytokine production - They block the inflammatory reaction by inhibiting lymphocytes from producing vasoactive amines, TNF, IL-4, IL-5 etc. 5. Omalizumab → Monoclonal antibodies against soluble IgE They bind to the Fc𝛆RI and RII of basophils/mast cells - blocking IgE the inflammation process. They can't bind to IgE when it's bound to the effector, only if it's freely soluble.

immunodeficiency disorders that affect the innate immunity

1. Chronic granulomatous disease 2. Leukocytes adhesion deficiency 3. Mendelian susceptibility to mycobacterial diseases 4. Chediak Higashi syndrome - Defects in lysosome-phagosome fusion → the bacteria is not destroyed 5. NK cells deficit

Innate responces to extracellular barteria

1. Complement system via alternative and lectin pathways Phagocytes will be activated → mediating cytokines* → inflammatory processes*IL-6 | IL-1β | TNF-α | IFN-​γ | IL-12 IFN-​γ is considered between innate & adaptive | target cells activate NF-𝞳B genes that trigger inflammation 2. Other T cells of epithelial barriers: Unconventional T lymphocytes (γδ TCR, 10% of T cell population) Natural killer cells Mucosal associated invariant T cell (MAIT) # Acute phase proteins produciton 3. Innate Lymphoid cells (ILC) are also important for fighting extracellular bacteria. Mainly ILC3 which secretes IL-17 | IL-22 | GF-CSF

Heavy/ Beta chain recombination

1. DNA loops bring two RSS together - V(D)J recombinases recognises RSS and brings the exons together 2. RAG1 and RAG2 cut DNA at RSS - Recombination of V and J exons may occur by deletion of intervening DNA and ligation of the V and J segments. or, if the RSS is 3' of a J segment, by inversion of the DNA followed by ligation of adjacentgene segments 3. Recombinases recombine DNA (Artemis, Ku)

IgE Receptor Complex

1. FcεRI - is a receptor complex that binds to IgE with the greatest affinity - Found on: mast cells & basophils | to a lesser extent - eosinophils, Langerhan cells, some dermal macrophages and activated monocytes. - Alpha chain (Binding), Beta chain (Signalling), 2 gamma chains (Signalling; two sulfide bonds) 2. FcεRII (CD23) - is another complex that can bind the Fc fragment of IgE - but with much lower affinity. Generates the same result - Enhancement of IgE production. - Has two subtypes: FcεRIIa subtype - found on follicular B cells = needed for more IgE production (positive cycle) - FcεRIIb subtype - found on B cells, T cells, macrophages, DCs

Examples of acquired immunodeficiencies [mentioned 7 types]

1. HIV 2. Influenza virus infection = may lead to a transient lymphocyte downregulation 3. Denutrition or malnutrition (esp. in old pop.) 4. Iatrogenic conditions (e.g CT, RT in cancer Tx) 5. Metastasis/ Leukemia in bone marrow = no production of lymphocytes 6 Pharmacological immunosuppresion 7. Asplenia (due to sickle cell disease or splenectomy) → ↓ phagocytosis of bacteria in the bloodstream

3 Types of graft rejection

1. Hyperacute - Due to presence of pre-formed Abs in the recipient. 2. Acute - Due to Allogenic MHC molecules of the grafts [Only therapy is immunosupression] 3. Chronic - Due to minor Ags; Fibrosis of the organ. [No therapy]

Function of induced regulatory T cells

1. Induced Tregs are non autoreactive; they recognize non-self antigen that are 'good' for the body and do not need to be fought against (e.g. microbiota). 2. They produce anti-inflammatory cytokines (e.g. TGF-β & IL-10) to inhibit the immune response against those 'good' antigens. 3. It is estimated that the proportion of FoxP3+ Tregs among CD4+ cells is about 2-fold greater in the intestine than in other tissues. Many of these Tregs are induced in the gut in response to antigens encountered locally.

Innate and adaptive immune mechanisms against intracellular bacteria

1. Innate: Control the infection; unable to eliminate. Macrophages interact with pathogens → release IL-2 & IL-15 → activating NK cells & ILCs → they in turn release specific amounts of IFN​γ - that allows correct activation & functioning of the macrophages (inducing production of ROS, NO, lysosomal enzymes). 2. Adaptive: Eliminate the infection. Activated T cells release more IFN​γ that acts on the macrophages *If needed - cytotoxic T cells (CD8+) are also activated

Difficulties of transplanation

1. MHC is a super polymorphic gene (the most heterogeneous in our genome) The most polymorphic are the chains for: HLA A, HLA B, HLA C + β chain of HLA DR These molecules are codominantly expressed, meaning that a person inherits and expresses an allele from both parents. Each of them has thousands of different alleles. Any mismatch between the donor and recipient, even one due to minor histocompatibility complex differences, will be eventually recognized as non-self and trigger a response against the graft (slower, but still present). 2. H-Y response - Males (only) have a human H-Y histocompatibility antigen derived from the SMCY protein encoded by the Y chromosome. A male-to-female transplant, can lead to rejection of the male graft by female recipients, even if they match at the MHC locus, due to this antigen.

Pharmacological approaches to obtain Immunosuppression - give 7 examples.

1. Monoclonal antibodies: Anti-CD20 (B cell marker) for acute rejection caused by Ab production → leading to B cell depletion → depletion of antibody pool. Anti-CD52 / anti-thymocyte Abs → T cell depletion 2. Calcineurin inhibitors: Cyclosporin A or FK506 (Tacrolimus) → both inhibit calcineurin → block T cell activation 3. mTOR inhibition: Rapamycin (Sirolimus) → blocks mTOR by binding to FKBP → suppress IL2-mediated proliferation 4. Belatacept : = Fusion (recombinant) protein that blocks B7:Chimeric molecule composed of part of the Fc fragment of IgG and CTLA-4 domain that can bind to B7 with a higher affinity than CD28 The MHC-antigen recognition by the T cell can still occur, but the drug prevents CD28 costimulation → no proper T cell activation → T cell Anergy 5. Anti-40CDL: blocks the binding of the T cells CD40L with CD40s found on APCs 6. Anti-metabolites 7. Anti-inflammatory drugs/ Corticosteroids

Different Antigens that lead to B cell activation (mono vs. multi- valent)

1. Multivalent antigens = Multivalent = an antigen with multiple copies of the same epitope → can simultaneously interact (cross link) with several BCRs - at least 2 BCRs have to be bound for an activation. 2. T-Dependent antigens = Monovalent antigens = have only one copy of each epitope (→ 1 antigen can't simultaneously bind several BCRs) → they need the 'help' and interaction of T cells.

3 steps to prevent hyperacute rejection

1. No pre-existing alloantibodies due to previous transplant 2. Donor and recepient have the same type of antibodes (ABO blood typing) 3. HLA typing from both donor and recipient. 4. Repeat PRA test to make sure MHC matches MHC. If PRA is negative transplant still can happen but immunosuppresive drugs are given as well. * Anatomical match should also be considered.

3 ways lymphocytes can respond to antigens

1. Normal immune response → lymphocytes encounter an immunogenic antigen → undergo proliferation & differentiation 2. Tolerance (much more common) → upon antigen encounter → no imm. response / anergy / apoptosis 3. Ignorance → no exposure to the antigen / encounter with a non-immunogenic antigen - occurs in "privileged areas" (i.e. brain, testicles, ovaries, eyes) - tissues that need to be preserved, and an immune response elicited in them may damage them. The brain has a small degree of inflammation but no lymphocytes.

5 Functions of the complement system

1. Opsonisation of bacteria 2. Lysis of targeted cells = form a Membrane Attack Complex (MAC), which creates a hole in the bacterial cell membrane 3. Induction of inflammatory responses = → act as chemotaxins - recruit neutrophils, eosinophils, monocytes, macrophages to site of inflamm. → act as anaphylatoxins - help basophils & mast cells degranulate → release proinflammatory molecules (e.g. histamine & heparin) into the area | They're cleaved by carboxypeptidases smooth muscles contraction + bronchial constriction + ↑ vascular permeability. 4. Dispositions of immune complexes = Transport via RBC to liver and spleen for disposition 5. Potentiation of B cell activation in response to thymus-independent agents = coreceptor (CR2) that potentiates the signal from the BCR that binds a specific complement component.

Stages of T lymphocyte maturation

1. Pro T and Pre T - active proliferation state -> mitosis and increase in number 2. Development - cell transforms from a double negative (DN) to a double positive (DP) 3. TCR rearrangement - different chains are recombined at the same time

Cancer derived antigens

1. Products of oncogenes or TSGs 2. Mutants of cellular genes not involved in tumorigenesis 3. Products of silent genes 4. Products of normal genes expressed in a huge amount or by a huge amount of cells 5. Products of oncogenic viruses 6. Oncofetal antigens 7. Glycolipids of glycoproteins 8. Differentiation antigens

Two phase mechanisms in allergy

1. Sensitization: Allergen encounter --> stimulation of Th2-type cytokine release by ILC type 2 --> DC maturation and presentation of antigen --> presentation to T cells in lymph nodes --> T cells become Th2 and IL-4-producing Tfh 2. Activation: Upon a subsequent encounter Allergen crosses the epithelium for the 2nd time → immediately encounters IgE on surface of mast cells + basophils Early phase → multivalent allergen binds to at least 2 IgE - Cross-linking of multiple FcεRI → degranulation of the cells - secrete preformed vasoactive mediators (e.g. histamine, serotonin, proteases) Intermediate phase → secrete lipid mediators (e.g. prostaglandins, leukotrienes, PAF) - fast effect on arachidonic acid --> faster protein synthesis (of cytokines and chemokines). Late phase → secrete cytokines & chemokines (e.g. IL-4, IL-5, IL-13, TNFα) via activation of gene expression, to sustain prolonged inflammation.

Examples of non-autoimmune diseases caused by type 3 hypersensitivity

1. Serum sickness = A reaction to proteins in antiserum derived from a non-human animal source; May result after usage of passive immunotherapy. (See graph) Administrations was common in past, against diphteria and others --> More common in the past. Graph: Immuno-complexes increases over time 2. Farmers lung = due to inhalation of hay dust and mold spores 3. Arthus reaction = experimental vasculitis due to SC injection of foreign Ags into an immunized subject

Pathogen Immune Evasion / Virulence mechanisms:; 2 mechanisms

1. Superantigens 2. Protein SSLP7

CAR-T production

1. T cells are isolated from a patient's blood 2. A new gene encoding a chimeric antigen receptor is incorporated into the T cells 3. Engineered T cells are now specific to a desired target antigen 4. Engineered T cells are expanded in tissue culture 5. Engineered T cells are infused back into the patient

Differences between an antibody-secreting plasma cell and its mother cell

1. The plasma cell is much larger (cytoplasm:nucleus ratio ↑) 2. The endoplasmic reticulum becomes more prominent + alterations in the secretory pathway 3. The Ig production is increased ↑ + transition to the secreted form of the Ig heavy chain.

4 types of vaccines

1. Whole microorgansisms 2. Purified antigens 3. Inactivated toxins 4. Engineered. vaccines: DNA, RNA, Viral plasmid based, Reverse vaccinology 5. (Conjugated vaccines - Older)

Ras-MAP kinase pathway in T cell activation (Grb-2 role in signalosome)

1. ZAP-70 phosphorilates LAT; That binds Grb-2 which provides as docking site for GTP/GDP exchange factor SOS. 2. SOS converts Ras·GDP to Ras·GTP. Ras·GTP activates a cascade of enzymes, which culminates in the activation of the MAP kinase ERK. = Synthesis and activation of transcription factors.

entry of HIV into the cell

1. gp41 & gp120 bind to CD4 → conformational changes in gp120 that promotes: 2. Binding of gp120 to CCR5 or CXCR4 → conformational changes in gp41 → exposure of a fusion peptide that can enter the host's cell mb ⇒ physical fusion 3. Capsid broken down 4. Genome retro-transcribed into DNA → enters cell nucleus to get integrated with the host cell's genome (via LTR sequences) = now called a 'provirus' 5. The provirus remains dormant (not expressed, not transcribed) until the T cell gets activated 6. Transcribed RNAs are exported into cytosol via a protein complex that creates a channel and are then transcribed into viral proteins → assembly of new virions → bud out of the cell → and the cycles start again

Ways to turn off signalling from T and B cells

1. ubiquitination 2. Through phosphatases: dephosphorylate ITAM sequences → inactivate them and stop the transmission When a cell is strongly activated, it starts expressing death receptors, such as the Fas receptor or the TNF receptor → initiate extrinsic apoptotic pathways Once the receptors are activated, T cells undergo apoptosis

D diversity segment

23 segments found between the V and J segments in the IgH locus; there should be the recombination of the original sequence to obtain something that wasn't there before. Light chains don't have them.

Structure of IgG

4 chains; each chain: one variable (V) region at amino end Two binding sites → each formed by one light and one heavy V one constant (C) Light chain → kappa or lambda.(two isotypes, κ -60% or λ - 40%, and each B cell can only produce one or the other) - Do not differ in function. CDR - complementary determining regions (3) - CDR1/CDR2 → in V fragment - CDR3: heavy → D fragment; light → V or J fragment Idiotype →variability of CDRs groups

Hypersensitivity diseases; What factors are involved?

= An excessive and inappropriate reaction to a certain antigenic stimulation, mediated by the immune system. Factors involved: Genetic predisposition to mount the reaction Environmental exposure to an antigen Their interaction leads to either → homeostasis (balance) OR dysregulation (uncontrolled response, breakage of self-tolerance, autoimmunity)

Mendelian Susceptibility to Mycobacterial Diseases (MSMD)

= Defect in the expression of IFN-γ and IL-12 receptors IFN receptors can be defective, breaking up the IFN-γ-IL-12 axis → blocking the activation of Mø. - genetic mutation (recessive/dominant/X-linked) in the R1 chain of the IFN-γ receptor (a heterodimer)→ defects in the IFN-γ signaling pathways Forms - depend on the type of mutation: Recessive - both alleles mutated → R1 chain doesn't mature and reach cellular mb → total block of IFN-γ pathway Dominant (not truly 'dominant', more like 'incomplete dominance') - mutation can be either: - Clinical presentation: most apparent in homozygous variations (dom/rec form): ↑ susceptibility to poorly virulent mycobacteria [e.g. BCG vaccines & environmental mycobacteria (EM)]

Delayed type hypersensitivity (DTH)

= The classical T cell-mediated inflammatory reaction Primary infection / immunization → memory Th1 cells developed (sensitization) → re-infection → the Th1 cells are readily activated (→ activate macrophages) * DTH is seen in Tuberculin skin test (AKA Mantoux Intradermal reaction) for MTB: * Immune system challenge: mycobacteria antigens injected intradermally → within 18-48hrs - DTH reaction: a local reaction is seen due to the infiltration & accumulation of activated macrophages = local inflammation = induration & erythema. Reaction is normal but if chronic/exaggerated → tissue damage * Persistent infections → Chronic DTH reactions w/ formation of granulomas (Macs are continuously recruited and from a Granuloma)

Graft VS Tumor/Leukemia (GVL - leukemia or lymphoma)

A case in which the graft's alloreactivity is actually beneficial for the recipient - the graft T cells react against tumor antigens of the recipient's Acute Myeloid Leukemia → better survival. Mechanism not so clear, may be due to a mismatch between the MHCs and consequent mismatch of NK receptors. At the first wave of newly-produced NK cells - the new NK cells (stemming from the transplant) recognize the MHC of the leukemic cells as non-self and attack them. In subsequent waves, the NKCs will be educated to tolerate all cells of the recipient.

Multiple sclerosis

A chronic disease of the central nervous system marked by damage to the myelin sheath. Plaques occur in the brain and spinal cord causing tremor, weakness, incoordination, paresthesia, and disturbances in vision and speech * Th1 & Th7 react against self myelin antigens → inflammation w/ activation of macrophages around nerves of brain & SC + myelin destruction ⇒ abnormalities in nerve conduction & neurological deficits

CD 3 receptor structure and function

A heterodimer made of 2 of 3 chains: epsilon (ε), gamma (γ), delta (∆) It's also the biomarker of T lymphocytes Since it's universal (on all T cells) → not involved in antigen recognition, but it helps in signal transmission through its long tail that contains an ITAM sequence protruding into the cytoplasm * Pan T

TCR receptor structure

A heterodimer made of α + β chains, connected by a disulfide bond + a tail Each chain has 2 extracellular domains: Constant region (C) Variable region (V) → outer | devoted for antigen recognition The tail is very short (5-12 AAs) - protrudes into the cytoplasm (no signalling function → needs an adaptor protein). * αβTCR (ony in 10% it's the γ∆TCR variant)

Myasthenia gravis

A long-term, autoimmune, neuromuscular disease leading to various degrees of skeletal muscle weakness (mainly muscles of eyes, face, and swallowing) Pathogenesis: auto-Abs against the nicotinic ACh-Receptor in the NMJ OR against proteins that influence the AChR (MuSK - Muscle specific kinase, LRP4, Agrin, Titin)→ no NA+ influx into the myocyte in response to neuronal impulse → progressive muscle paralysis Treatment: Acetylcholinesterase inhibitors (to ↑ muscle function directly) Immunosuppressants to ↓ the autoimmunity Thymectomy - not always effective (Removal of thymus)

processes of B cell activation

A naive B cell encounters a specific antigen via its surface Ig receptor (IgM/IgD) → Helper T cell + other stimuli generate signals for the complete activation of B cells → B cells proliferate (takes a few days) → the activated progeny undergo differentiation into: - Plasma cells → secrete antibodies (or undergo isotype switching) - High-affinity Ig-expressing cells → undergo affinity maturation / persist as memory cells * The B cell can recognize - internalize - process - present the antigen via MHC class II → so that the T cells can recognize it

Costimulation

A secondary signal which immune cells rely on to activate an immune response in the presence of an antigen-presenting cell. In T cells: Signal 1 (from TCR) and signal 2 pass through the costimulatory invariant (no recombination) receptor molecule (here CD28) - Lack of a second signal leads to an anergic state

Genetic Mechanisms of heavy chain isotype switching

A selected B cell is stimulated by IL-4 (from TFH) → it's induced to switch into IgE (needs to express the ε CH segment). * The DNA flanks and loops → so that Sμ can recombine with Sε → the intervening ('redundant') DNA is cut and lost → this and further RNA splicing after transcription brings the VDJ exon closer to Cε → to be translated and create the IgE molecule.

Leprosy

A skin and nerve disease that causes open sores on the body (Serious disease). Has 2 forms: 1. Tuberculoid -Strong immune response → disease contained. 2. Lepromatous - Strong immune suppression → disseminated infection

Adjuvants

A substance that increases and/or modulates the immune response to a vaccine * stimulate the innate and inflammatory responses, promoting expression of costimulatory molecules to T lymphocytes → increase vaccine efficacy. Old adjuvants mostly worked by causing precipitation and persistence of the antigens within the tissues → increased exposure of the immune system to the antigen New adjuvants under development use innate immunity agonists like Toll-like receptors (which are PRRs), acting as PAMPs → trigger innate immunity response → cytokine production (e.g. IL12, IFNγ) to activate lymphocytes (adaptive immunity). - have possible side effects (e.g. fever, malaise, headache - normal when the innate immunity is activated) → people are less likely to get vaccinated

Systemic Lupus Erythematosus (SLE)

A systemic, autoimmune disease [→ ++ in females (10:1)] Auto-Abs against: 1. dsDNA - nucleosomes, histones, spliceosome 2. Extractable nuclear Ags - Ro/SSA, La/SSB 3. Mitochondrial components 4. Cardiolipin * Deficit in the classical pathway. * Thrombocytopenia * Polymorphism of FcyRIIB and HLA-DR3 [We don't know why] * Mutations in TREX1 gene Therapy: Steroids or monoclonal Ab (Belimumab)

Enzyme complexes involved in VDJ

A tetramer endonuclease complex in a dimer (RAG1 & RAG2)→ Role: binds the DNA in the RSS and cuts it out Artemis (a complex of enzymes also involved in DNA repair: Ku70, Ku80, XPRCC4, DNA Ligase)→ Role: PA opens up the hairpin + joins the two open ends together (if gaps need to be completed - P nucleotides are added).

NETHERTON'S SYNDROME

A very rare autosomal recessive disease - Severe hyperproduction of IgE * Due to a mutation of SPINK5 (Serine protease inhibitor Kazal-type 5): - Associated with atopy - Inhibits proteases released by staphylococcus aureus and other bacteria.

Pathogenesis of type 4 hypersensitivity

A) CYTOKINE-MEDIATED INFLAMMATION Helper T cell activated near normal tissue → releases many cytokines (above) → more immune cells are activated (neutrophils or macrophages) → damage of the nearby tissue B) T CELL-MEDIATED CYTOTOXICITY CTLs killing target cells → tissue damage

The function of AIRE in deletion of T cells in the thymus

A, The AIRE proteinis part of a complex that regulates the expression of tissue-restricted antigens (TRAs) in medullary thymic epithelial cells (MTEC). Peptides derived from these antigens are displayed on the MTEC and recognized by immature antigen-specific T cells, leading to the deletion of many self-reactive T cells. B, In the absence of functional AIRE, these self-reactive T cells are not eliminated; they can enter tissues where the antigens continue to be produced and cause injury * Mutations in AIRE are a major cause for autoimmune diseases [autoimmune polyendocrine syndrome type 1(APS1)]

ABO blood groups

ABO surface antigens Are found on RBCs and on endothelial cells - why it's important in all types of transplants Made of mb glycoproteins/glycolipids. Basic structure = Antigen H (oligosaccharide) attached to Ceramide on the cell surface. Group O → universal donors (since they have no antigens → not considered non-self by other groups) Group AB → universal recipients (since they have no NAbs against other blood groups)

Autosomal recessive SCID; genetic source

ADA gene mutations: Most common AR SCID ADA encodes for the enzyme adenosine deaminase - which is involved in metabolism of nucleotides Mutation → accumulation of catabolites of nucleotide metabolism - the B & T cells are very vulnerable to these catabolites → get intoxicated (+ problem in DNA synthesis) → failure in maturation & proliferation → cell death Behavioral abnormalities, deafness, hepatic problems PNP gene mutations: PNP encodes for the enzyme purine nucleoside phosphorylase - which is also involved in metabolism of nucleotides AK2 gene mutations: AK2 encodes for adenylate kinase 2 Mutation → Reticular Dysgenesis (De VAal disease): The most severe form of SCID Affects T & B cells + other myeloid & lymphoid precursors→ almost complete absence of WBCs RAG enzyme, DNA-PK, ligase 4 gene mutations: Mutation → Omenn's syndrome: Mutations only cause a slight alteration of the enzyme → somatic recombination problems

Rheumatoid arthritis

AI, progressive, inflammatory disease of the synovium ⇒ destruction of joint cartilage & bone A chronic form of polyarthritis Chronic immune response → can lead to tertiary lymphoid organs in the synovium → can maintain & propagate the local immune reaction Affects small & large joints of extremities (fingers, toes, wrists, ankles, shoulders, knees) F:M = 3:1 Used to be deadly due to systemic complications * No proper treatment

Somatic Hypermutation (SHM) (Affinity maturation)

AID enzymes (& others) act on Ig Variable (V) genes by generating Cytidine-to-Thymine point mutations in specific hotspots (located on the CDRs). ⇒ The final result of these changes is in the antigen affinity (not in the antibody specificity), that is increased.Only these high-affinity antibodies will later recognize antigens on FDCs (in the light zone) → process them → present them to TFH → be able to survive and return to the dark zone for further proliferation before they exit the germinal center *The mutations accumulate in each cell cycle when the B cells are in the proliferative phase. *This process occurs in the dark zone of the germinal center

DAG in the T cell signalosome

Able to activate PKC, a kinase that can induce the activation of the TF NF-kB 1. Activation of the IKK complex that phosphorylates IkB 2. allows Ubiquitination and degradation of IkB, allowing NF-kB to enter inside the nucleus * NF-kB has a dimeric structure made of p50 linked with RelA

Abnormal physiologic responses without cell/tissue injury caused by type 2 hypersensitivity; Give 2 examples

Abs (often auto-Abs) may act as agonists/antagonists of diff. receptors (not cytotoxic - not producing tissue damage) → hypo-/hyper- activating → pathogenicity: E.g. Anti-TSH Abs that hyperstimulate the thyroid stimulating receptor → hyperthyroidism in Graves disease E.g anti-Acetylcholine receptor Abs that bind to the receptor preventing binding of Ach → flaccid paralysis in Myasthenia Gravis

Type 3 hypersensitivity

Accumulation of immune complexes (antigen-antibody complexes) that have not been adequately cleared by innate immune cells, giving rise to an inflammatory response and attraction of leukocytes. * Can be immune and autoimmune 1. immune complex formation, which involves the binding of antigens to antibodies to form mobile immune complexes. 2. immune complex deposition, during which the complexes leave the plasma and are deposited into tissues. 3. the inflammatory reaction, during which the classical pathway is activated and macrophages and neutrophils are recruited to the affected tissues. * Symptoms appear within a few hours

Roles of T cell activation (Final gene expression goal)

Activation of gene expression for: •Clonal expansion •Differentiation (Th0 à Th1, Th2, Th17, Treg, etc.) •Effector Functions (cytokine production, cytotoxicity) * Process if very fast

Affinity and avidity of antibodies

Affinity - The specificity between the antibody and antigen, relying on the nature of the interaction rather than the number of interactions. Is calculated using the dissociation constant (Kd) - Avidity - total binding strength of a molecule with more than one binding site. IgM, for example, will have a very high avidity (See pic)

structural changes in antibodies during humoral immune response

Affinity maturation - somatic mutation at the level of the variable domain of both the light and heavy chain that, by chance, increases the affinity without changes to the function. Change from membrane to secreted form - the transmembrane portion stops being expressed so the molecule becomes completely soluble. It doesn't affect the antigen recognition but goes from B cell receptor function to effector function. Isotype switching - Change regarding the constant part of the molecule, so the antibody will be identified as a whole other type of immunoglobulin. Also doesn't affect the antigen recognition, but it will have a whole new set of functions. - Affinity maturation and isotype switching usually occur simultaneously, since their mechanisms rely on the same enzyme. Therefore, IgG and IgM differ not only on the constant domain but also on the variable domain, having different affinities.

Dampening of T-cell activation by ubiquitination

After T and B cells have done their job, they need to be deactivated → inactive process called monoubiquitination, carried out by upstream kinase such as ZAP70 and ζ-chains Cbl-b - After being tagged, T and B receptors are carried to proteasomes to be degraded.

PIDs affecting B cell-mediated immunity

Agammaglobulinemia; X linked, - Hypogammaglobulinemias: In the newborn, CVID, - Hypergammaglobulinemias: Hyper IgM, Selective deficit IgA, SCID, X scid,

Antibodies variability and types

All have the same basic characteristics but have a huge variety in the Antigen binding site Immunoglobulin M (IgM) Immunoglobulin D (IgD) Immunoglobulin G (IgG) Immunoglobulin A (IgA) Immunoglobulin E (IgE)

Hypersensitivity vs. allergy

Allergy involves IgE, but this is a strict definition. E.g., type 4 hypersensitivity does not involves Ab therefore it is strictly does not considered an allergy

Indirect Recognition of Alloantigens

Allo-MHC molecules are captured and processed by recipient APCs, and peptides derived from the allogenetic MHC molecules are presented in association with self MHC molecules - peptides from the allogeneic MHC molecules are displayed by host APCs and recognized by T cells like conventional foreign protein antigens. - Can activate both Th and CTc. * If presented by recipient APc = Indirect recognition.

Unconventional T lymphocytes & Mucosal associated T cells; what is peculiar about these guys?

Although they're T cells, their specific repertoire is not so big; rather than identifying specific antigens, they can identify antigen families (why they're considered innate) → they're involved in the inflammatory process too. # They produce acute phase proteins.

Examples of adjuvants

Alum - the first adjuvant introduced for humans | made by a mineral salt of Aluminium | used for vaccines against many infectious diseases Freund's adjuvant - the most effective | but too toxic for humans | formed by dead bacteria in mineral oil MF59 - squalene / squalene-derived oils emulsified in water | used against influenza Recently, many other adjuvants were introduced, some still developed using new strategies.

Pemphigus

An acute or chronic disease of adults, characterized by occurrence of successive crops of bullae that appear suddenly or apparently normal skin and disappear, leaving pigmented spots. - IgG produced against EC5 ⇒ form immune complexes--> Crosslinking of two EC5 domains via the IgG--> When two molecules of desmoglein (Forms desmosomes) bind to two BCRs via EC1 & EC2 on a B cell → B cell activated (by cross bridging) Activated B cell produces Abs against EC1 & EC2 → can damage desmosomes & epithelia

Haemolytic disease of the newborn

Anti Rh+ antibodies of a sensitised Rh- mother cross the placenta and destroy the RBCs of an Rh+ baby, causing Haemolysis and potentially death. In 2nd pregnancy the small amount of foetal blood that is in touch with the mother circulation is enough to trigger a reaction. * Example of type 2 hypersensitivity * Problem is the 2nd pregnancy after formation of memory B cells that get stimulated to produce anti-Rh+ IgMs & IgGs that can cross the placental barrier causing detrimental effects

Hashimoto's Thyroiditis

Anti-TSH receptor Abs that bind to a diff. epitope than the Abs in Graves' disease, so instead of upregulating the TSH receptor, they reduce the activity of the thyrocytes ⇒ hypothyroidism * Removal of thyroid; Hormone replacement therapy; Steroids.

Rh antigen rhesus

Antigen Rhesus (Rh): Found on RBCs; 15% of population don't express it. Non-glycosylated protein, encoded by the RhD gene Rh+ → most people → don't react to RhD antigens, since they already have them. Rh- → 15% of population (no expression of the RhD gene) → if sensitized they can form anti-RhD IgG antibodies - it's IgG & not IgM - important for pregnancies.

Antigenetic Drift vs Antigenetic Shift

Antigenic drift = a small mutation leads to a small but significant change in the RNA structure Mutations can accumulate overtime. Influenza virus has two immunodominant antigens; N = Neuraminidase and H = Hemagglutinin Drifts in these antigens are enough to overcome our immune system → why we need different influenza vaccines every year. Antigenic shift = a dramatic phenomenon, in which an entire RNA segment is exchanged between different virus strains → creating new strains. It happens due to reverse transcriptase which is very error prone → more mutations In some cases - our immunity can have a mild protection against the new antigens → asymptomatic patients

Antigens

Anything that binds antibodies; have epitopes. - Immune system should differentiate self and non self antigens - Have epitopes - Haptens

Complement Receptors (CR#)

Are expressed in many cell types and promote diff. activities, e.g: - CR1 is a complement inhibitor - CR2 potentiates the activation of B cells in response to antigens opsonized with C3D / iC3b

T cell development in the thymus

At the cortex (positive and negative selection): - Death by neglect → death of cells that don't recognise any MHC During migration to medulla: positive and negative selection - Positive selection → cells that weakly or don't even recognise self-MHC - Negative selection → death of cells that bind strongly to self-Antigen

AUTOIMMUNE DISEASES - related to Type II hypersensitivity

Autoimmune hemolytic anemias (AIHA): Extravascular hemolysis of RBCs (due to IgG-mediated phagocytosis in spleen) Intravascular hemolysis of RBCs (due to IgM-mediated complement activation)→ RBCs lifespan is ↓ from 100-120 days to just a few days, leading to anemia. Autoimmune thrombotic thrombocytopenic purpura Auto-Abs against ADAMTS13 resulting in decreased degradation of von Willebrand factor → hypercoagulation, hemolysis, bleeding Pernicious anemia = Destruction of intestinal villi = lack of vitamin B Goodpasture syndrome Pemphigus (Bullous Skin disease)​ Graves' disease (or Basedow-Graves disease)​ Hashimoto's Thyroiditis Myasthenia gravis​

CLASSIFICATION BY ORIGIN of the grafted tissue/organ

Autologous / autotransplant - when the donor is the recipient (one donates to himself). E.g. blood autotransfusions, chondrocytes, and skin autotransplant Advantage: no rejection of the body Isogenic/Syngeneic transplant - the donor is a an identical littermate of the recipient (e.g. monozygotic twins , that are diff., but genetically identical since they're from the same ovum) Advantage: no rejection of the body Allogeneic / allotransplants - the donor is genetically unrelated to donor (but same species) Most transplants are allogenic. But could also cause rejection by immune responses Xenogenic / xenotransplants - the donor and recipients are of different species. Currently not pursued because the rejection is inevitable. However, maybe in the future we'll be able to breed animals so they present human antigens, and thus avoid the host's recognition of the donor as foreign.

Isotype (class) switching

B cells activated by helper T cell signals (CD40L, cytokines) undergo switching to different Ig isotypes, which mediate distinct effector functions - The change is only in the constant region (C) of the heavy chain - Every C segment comes with I & S segments upstream to it: I (initiation of transcription) exon (Iμ, Iγ, Iε) S (switch) region (Sμ, Sγ, Sε) E.g. ⇒ Iε-Sε-Cε locus *Only C​δ doesn't have I & S - done via genetic recombination (downstream of VDJ). - occurs during B cell activation and not maturation.

Hyper-gammaglobulinemias; Hyper IgM syndrome

B cells are produced in the same amount as in healthy individuals, but the problem is that all the Igs are IgMs, since the immunoglobulin class switching recombination (CSR) is blocked (due to mutations) Almost total absence of IgA, IgG Abnormally high levels of IgM + only IgMs are produced in response to infections Etiology mutations in genes that code for CD40, CD40L, or downstreamproteins of the pathway they drive (AID, UNG, NEMO) - Has 5 types - Effects Recurrent localized or generalized infections by poorly virulent pathogens Recurrent pulmonary tract infections (Pneumocystis Jirovecii) and GI tract infections (Giardia lamblia, Cryptosporidium, Entamoeba histolytica). General malfunctioning of cell-mediated immune response Histology shows that the germinal centers in lymph nodes are underdeveloped

Extracellular bacteria infections

Bacteria that infect the mucosae or epithelia - they don't enter cells! * Response is either adaptive or innate. 1. Innate = Complement system; Alternative and lectin patways; Innate lymphoid cells; Other T cells of epithelial barrier. 2. Adaptive = ativation of humoral response + T helper cells

Intracellular bacterial infections. What is special about this protective immunity against this type?

Bacteria use the cell as a 'safe haven' to avoid the body tissues/blood that is full of circulating immune cells. But the space is limited, once they proliferate too much they have to leave the infected cell in order to find some other cells to invade and keep on multiplying. * Humoral immunity is not relevant as antibodies can not enter the cells:

Immune evasion of schistosoma

Big dimensions of the parasite → can't be phagocytosed Acquisition of new antigens → antigenic variation helps escape the immune system. Hard integument → the pathogen can avoid lysis after complement activation. Cannot be killed by CD8+ CTLs since they're multicellular - need to be killed by poisons.

Therapeutic Approaches for hypersensitivities; blocking T cell activation techniques

Blocking T cell interaction with APC by removing costimulation A chimeric molecule that competes w/ B7 (on APC) for the CD28 receptor (on T cell) (e.g. belatacept) → TCR alone is not enough to elicit a response Inhibiting downstream signaling following receptor-ligand interaction: Calcineurin inhibitors (e.g. cyclosporine, tacrolimus) Kinase inhibitors JAK inhibitors Blocking T-cell proliferation moAbs that target specific T cell populations → cytotoxicity destroyed lineage Limit proliferation via anti IL-2R moAb Blocking downstream effects of inflammation moAbs against TNF, IL-1, IL-6R

Mechanisms of T cell costimulation by CD28

CD28 binds B7-1 (present upon activation of APc) CD28 engagement induces signalling pathways that enhance TCR signals or trigger additional signals, all of which stimulate the expression of survival proteins, cytokines, and cytokine receptors: - promote cell proliferation; and induce differentiation toward effector and memory cells by activating various transcription factors

CD8+ Cross-Priming

CD8+ Cross-priming = when a CD8+ T cell targets a tumor cell presenting a certain antigen. But to activate the CTL and lead to tumor-specific differentiation, co-stimulation is required* - in this case - helper T cells are needed - Tumor cell / parts of it - engulfed by an APC → processed → a peptide is presented on MHC II - MHC II is recognized by a CD4+ T cell - CD4+ T cell secrete several cytokines to provide costimulatory signals for CD8+ T cells - CD8+ T cells are differentiated into tumor-specific CTLs → can generate a cytotoxic response against the tumor cells.

Co-inhibition examples

CLTA-4 & PD1 CLTA-4: recognise and bind B7-1 and B7-2, then if the ligands are expressed strongly - CD28 prevails. if weakly - CLTA-4 prevails. PD1: Recognise and bind PD-L1 and PD-L2 Binding suppresses the activity of the cells * Monoclonal antibodies can inhibit PD1

transition to the secreted form of the Ig heavy chain.

Caused by alternative RNA processing of the heavy chain mRNA For the antibody-secreting cells the regions encoding for the transmembrane (TM) and cytoplasmic (CY) are spliced out from the mature mRNA, while the tail piece (TP) remains. The C-terminal ≈ 20 AAs forming the tail piece For the resting B cells (membrane-bound Igs) the TM & CY are found instead of the TP

Plasmodium

Causes Malaria. - Spread all over the world, but especially in tropical areas (e.g. central/south America, Africa, SEA) - 2017: 219 million cases | 435,000 deaths | 3.1 billion $ invested in malaria control - Note the life cycle

Direct and indirect tissue damage caused by type 2 hypersensitivity

Causing direct tissue damage: - Complement and Fc receptor-mediated inflammation: → induces recruitment of other inflam. molecules → local inflammation → neutrophils degranulate → ROS release → tissue injury - ADCC (Ab-dependent cellular cytotoxicity) mediated by NK cells - their CD16 receptors recognizes the Fc of IgGs → cell opsonization = target for phagocytosis - Phagocytosis of cells opsonized by Abs → tissue damage if the cell is a host (self) cell Causing indirect tissue damage: - Generic inflammatory reactions - close to site of antigen recognition by the IgM/IgG Ab.

Central vs. peripheral tolerance

Central tolerance → in the thymus and BM (primary lymph. organs).When there's a recognition of a self antigen by an immature lymphocyte, this could happen: - Deletion (apoptosis, negative selection) - Receptor editing (B cells) - Development of innate Regulatory T lymphocytes. Peripheral tolerance → in the peripheral tissues - needed when a T cell 'escapes' central T. When there's a recognition of a self antigen by a mature lymphocyte, this could happen: - Anergy (In B cells it also occurs in central tolerance) Deletion (apoptosis, negative selection) - Suppression (by Treg cells) - Downregulation of chemokines → hinders B cells from re-entering the lymph nodes so they don't proliferate & differentiate into plasma cells.

Checkpoints of lymphocyte maturation

Checks correct production of the pre-antigen receptors, which signalizes that recombination was successful and allows proliferation and maturation. Out-of-frame rearrangements don't express these receptors and, without the required signals for proliferation, the cell undergoes apoptosis.

4 reasons of antibody variability

Combinatorial variability (from somatic recombination) Joining variability [added P nucleotides (to fill the gaps) & N nucleotides (random insertion)] TdT is not expressed for the α chain of TCR → most of the variability is on the β chain RNA processing - the primary transcript is spliced to eliminate the parts between the J & C fragments → then the Poly-A tail is added → translation with the L (leader) sequence. Post-translational modification at the Golgi (addition of sugar prosthetic group).

Conjugated vaccines

Combines a weak antigen with a strong antigen as a carrier so that the immune system has a stronger response to the weak antigen.

lectin binding pathway

Complement system activation by polysaccharide residues on pathogens

Contact hypersensitivity

Contact dermatitis - small molecules easily enter the skin → act like haptens - they bind to self-proteins → modifying the proteins that are then recognized by T cells. * Causes contact dermatitis and an itchy, irritating, sometimes painful rash in most people who touch it due to the urushiol (organic compund)

NF-kB pathway

Contain 3 factors: 1. TNF 2. TLR Mediates the activation of NF-kB to produce pro-inflammatory cytokines 3. TCR Induces the activation of NF-kB through the activation of PKC All three converge by activating IKKβ, able to deactivate IkB through phosphorylation * cyclosporine (Drug) acts by avoiding the phosphorylation of IkB -> reduction of T-cell activation

DC from the donor vs cells/ antigens from the donors recognition by T cells

DCs from the donor cannot perform cross priming, they'd actually be directly recognized by T cells since they have non-self MHC molecules. Cells/antigens from the donor (not DCs) are recognized indirectly: taken up by recipient DCs → travel to closest lymph node → activate CD8+ & CD4+ cells → leave the lymph node → reach target (transplanted) organ where the same antigens are recognized & destroyed / inflammation initiated → organ rejection

Recombination Signal Sequences (RSS)

DNA sequences located on 3′ of each V gene segment, 5′ of each J segment, and flanking eachside of every D segment - highly conserved stretch of 7 nucleotides, called the heptamer, usually CACAGTG - Located adjacent to the coding sequence, followed by a spacer of exactly 12 or 23 non conserved nucleotides, followed by a highly conserved AT-rich stretch of 9 nucleotides, called the nonamer - During V(D)J recombination, double-stranded breaks are generated between the heptamer of the RSS and the adjacent V, D, or J coding sequence.

5 Defects of the complement system

Deficits in genes involved in the classical pathway Most common mutations: C1, C2, C4 genes Immune complex disease: not always immune deficiencies, can be: Type III hypersensitivity Systemic Lupus Erythematosus Deficits in genes involved in the MBL pathway (Mannose Binding Lectin) Most common mutations: MBL, MASP1, MASP2, C2, C4 genes Higher susceptibility to bacterial infections Improves with age Deficits in genes involved in the alternative pathway Most common mutations: Factor D, Factor P genes Susceptibility to Pyogenic bacteria and Neisseria infections Deficits in C3 Susceptibility to Pyogenic bacteria and Neisseria infections Possible immune complex disease Deficits in membrane attack components Include: C5, C6, C7, C8, C9 Susceptibility to Neisseria infections

SCID due to defects in T cell development

DiGeorge syndrome = deletion of a chromosomal fragment (~3 mill bases) in 22q11 → insufficient/absent development of 3rd & 4th pharyngeal pockets -->Lack of thymus → Immune deficiency (mainly T cells) that is transient (only up to 5 yo then other organs compensate)! MHC I Deficiency = T cells present, but processed antigens aren't presented to developing CD8+ T cells→ No CD8 T cells MHC II deficiency (Bare lymphocyte syndrome) = CD4+ T cells fail to develop→ No CD4 T cells. Autosomal recessive; mutations

Alternative pathway

Does not requrie antibodies -C3 present in the blood combines with factors B, D, and P on microbe surface -C3 splits into C3a and C3b, functioning the same as in the classical pathway

Double positive and double negative T cells

Double Negative (DN) = when the cell doesn't express CD4 or CD8 Double Positive (DP) = when the cell expresses both CD4 & CD8 + TCR (+CD3) - it then undergoes changes becoming Single Positive (immature still) - expressing either CD4 / CD8

HIV infection vs. time graph; 2 possible outcomes

EARLY ACUTE PHASE Viremia increases quite rapidly in first 3-6 weeks (forming a spike) after infection (T0) May present clinically with flu-like symptoms (fever, headache, sore throat, lymphadenopathy...) - usually underestimated While the CD4+ dramatically decrease IMMUNE SYSTEM RESPONDS → Viremia decreases ↓ Symptoms disappear Partial recovery of CD4+ LATENCY/SYMPTOMATIC PHASE (variable length, months-years) Steady but slow decrease of CD4+ Still enough to cover basal needs and prevent symptoms Viremia stable and quite low May be due to a response to antiretroviral therapy SYMPTOMATIC PHASE When CD4+ reaches <200 cells/mm3 - constitutional symptoms begin and risk of infections and other AIDS clinical features is high (= over AIDS) If left untreated - Viremia continues to increase CD4+ continue to drop Death ☠️

Effects on the foetus; haemolytic disease of newborn

Effects of the Abs on the second fetus: Destruction of fetal RBCs Jaundice Hepatomegaly and splenomegaly Possible hydrops and death Effects for the fetus if born alive:- Hyperbilirubinemia (massive fetal RBC destruction → bilirubin released (no longer disposed by mother's liver) - newborn's liver is not yet capable of dealing with the excessive bilirubin → leading to: Jaundice Possible kernicterus - deposition of bilirubin in basal nuclei of the brain) → spasticity and neurological damage that persists during life

Marginal Zone B cells

Especially in the marginal zone of the spleen, but also a bit in lymph nodes Limited number → produce antibodies with very limited diversity Mainly respond to polysaccharide and lipid antigens Produce IgM

CAR-T generations

First → only had the Z chain in the intracytoplasmic portion; limited responses in clinical trials. Second → CD28 and 4-1BB added Third → other costimulatories Fourth (TRUCK)→ NFAT → IL-12. Still studied

3 types of B cells

Follicular B cells (B2 / FOB) (Circulating B cells) Marginal Zone B cells B1 Cells

B1 cells

Found mainly in mucosal tissues Limited number → respond to a limited amount of antigens via specific Abs Mainly respond to polysaccharide and lipid antigens Produce IgM Often considered part of the innate immunity just because they live for a short time.

Circulating B cells (Follicular, B2/ FOB)

Found within the follicles in lymph nodes, spleen, Peyer's patches - Biggest group → Give rise to most high-affinity antibodies and memory B cells - Mainly respond to protein antigens - Produce IgM, IgG, IgE - Have a long-living response - Activation results in production of memory B cells

Types of genes in HIV

Gag genes - encode for core and matrix proteins - p17 & p24 Env genes - encode for envelope proteins - gp120, gp41 Pol genes - encode for the enzymes: Protease Reverse transcriptase Integrase Ribonuclease Regulatory genes - important for enhancing viral infection + blocking host response

Pathogenesis of Rheumatoid Arthritis

Genetic & environmental factors contribute to loss of tolerance to self antigens An unknown trigger sets an initial focus of inflammation in the synovial mb - cytokines recruit leukocytes (CD4 T cells, like Th1 & Th7 that activate macrophages) → produce pro-inflammatory cytokines that sustain the inflammation and also: - Make Fibroblasts express MMP → destroys matrix proteins of CT & joint cartilage - Make T cells express RANK ligand → binds to RANK receptor on osteoclast precursors to induce their differentiation & activation = osteoclast activity ↑ - Activate resident synovial cells → produce proteolytic enzymes (e.g. collagenase) *B & T cells can recognize citrullinated proteins (citrullination triggered by env. insults, e.g. smoking/infections...), which are more prone to degradation and thus antigen processing

Immune evasion by viruses (3 mechamisns)

Genomic rearrangement via Antigenetic drift & Antigenetic shift & Alteration of antigen processing + MHC presentation

Goodpasture syndrome

Glomerulonephritis and lung interstitial haemorrhages. Caused by The IgGs produced activate the complement system with recruitment of monocytes and mast cells. Targets Alpha 3 chain of Type 4 collagen (in the basal membrane) Auto-Abs accumulate on the basal membranes of organs that express that collagen chain * When the glomerulonephritis is due to (A) specific auto-Abs the deposition is precise, while if it's (B) immune-complex mediated (non-specific) the appearance is quite blurred Often happens in SLE - lupus (type III HS)

physiopathology celiac disease

Gluten proteins enter gut epithelium → tTG (tissue transglutaminase) deamidates (modifies) the peptides so that when they're uptaken by APCs and presented by MHC II (HLA-DQ2 or HLA-DQ8) to CD4 T cells, which get activated → attack and kill mucosal epithelial cells by finding Fas + they secrete IFN-γ and IL-15 to activate epithelial cells which then express stress molecules (e.g. MIC-A and MIC-B). These MIC can bind to NKG2D that is expressed by Intraepithelial lymphocytes (IELs, which are mainly CTLs) → activating the IEL to kill the epithelial cells ⇒ atrophy of the intestinal villi with crypt hyperplasia

Transplant rejection

Graft rejection displays the features of adaptive immune responses, namely, memory and mediation by lymphocytes. Primary (1st set) rejection - occurs within 2 weeks after an allotransplant Secondary rejection - occurs sooner, within a week after an allotransplant, in case the mouse was already exposed to the same donor immunosuppressed (naked) mouse will not reject the allotransplant. A proper working immune system will reject an allotransplant, while a suppressed one will accept it.

gram positive vs gram negative bacteria

Gram-Positive → have a very thick cell wall, built of several layers of peptidoglycan, teichoic acid, and sometimes lipoteichoic acid (e.g. MTB) - at the outer side of the cell mb. Gram-Negative → relatively thin cell wall made of peptidoglycan, with stackings of lipoproteins. They often have an outer membrane made of liposaccharides (LPS).

HIV vs. ageing

HIV-infected pts manifest signs of aging corresponding to older anagraphic age in normal subjects (i.e. their aging process is faster) The research hypothesizing this included (A) healthy people (former athletes), (B) HIV-infected pts, and (C) people sharing lifestyle with HIV-infected pts (e.g. drug abusers), but w/o HIV infection. → results showed the aging rate: B > C > A (HIV > shared-lifestyle > healthy) * HAART decreases the outcome

Immunity to yeast

Have a stronger adaptation to the human hosts → more adapted → better at escaping → immune system not so efficient against them. However, they don't kill the host, (if the immune response is working), unless there's immune suppression.

Common Variable Immunodeficiency (CVID)

Heterogenous group of disorders causing inefficiency in humoral response to anemia The most common type of hypogammaglobulinemia, but still rare Incidence: same in males and females S/S onset: 26 yo (20-30 yo) Types CVID-1 to CVID-6 | Based on the gene mutation + slightly diff. clinical presentation Effects Very low IgG, IgA, IgM *B cells are present! (helps DDx with XLA) Poor response to vaccination Diagnosis is difficult, since the etiology may involve only one gene or many genes altogether. → All pathways are involved in stimulating / co-stimulating the proliferation of B and T cells or in producing antibodies Treatment: periodical Ab infusions

Adaptive immune response to extracellular bacteria

Humoral response - Antibodies: Neutralization of bacterial products, e.g. toxins Opsonization - facilitates bacterial recognition to ↑ phagocytosis Complement activation: Via the classical pathway helps with bacterial opsonization Activation of inflammation through C3a & C5a In some cases - direct lysis of microbes T helper cells (which are the adaptive counterparts of ILCs - express the same TFs): Th1 (and ILC1) → express T-bet (a TF) and produce IFN​γ Th2 (and ILC2) → express GATA-3 (a TF) and produce IL-5 & IL-13 TH3 (and ILC3) → express ROR-γ (a TF) and produce IL-17 & IL-22

Hypo-gammaglobulinemias in the newborn

Hypo-gammaglobulinemia of the newborn Physiological in newborns 3m-1y (!) In-utero - the fetus gets IgG from the mother via the placenta After birth - progressive ↓ in the IgGs from the mother, as the baby starts producing their own There's a window in which the baby is particularly exposed (hasn't developed their own Abs yet, and maternal Abs are mostly exhausted)

Leukocytes Adhesion Deficiency (LAD); 3 types

ID disorder involving both B and T cells and is characterized by an inability of leukocytes to migrate to the site of infection to kill offending microbes. 3 types: Type 1: Mutation in CD18 gene → defective/deficient β-2 integrin Defect in the steady adhesion of leukocytes to endothelial surfaces Type 2: Defect in fucosylation | E-selectin deficiency Absence of Sialyl Lewis X glycan (the selectin ligand) Defective rolling Type 3: Defect in β integrins 1,2,3 Chemokines that drive the leukocytes to the right place are affected Defective rolling and defective platelet activation

Th2 and IL-4-producing Tfh action

IL-4-producing Tfh cells → drives isotype switching of B cells to IgE → the plasma cells produce ↑↑ IgE → circulate and reach tissue → bind to FcεRI on surface of mast cells (tissue-resident) and basophils (like mast cells, but circulating); at least 2 IgE are needed → both cells, coated with IgE, are sensitized to the allergen that caused the stimulus. Th2 cells → migrate back to site of allergic reaction → secretes cytokines (contributes to exacerbation of the situation)

T cell signaling downstream of PLCγ1 step 2

IP3 causes depletion of endoplasmic reticulum calcium, which is sensed by STIM1. PKC induces numerous cellular responses

Indirect recognition of alloantigens; is it MHC 1 or 2 ?

If it's MHC type I → CTL CD8+ activated If it's MHC type II → T helper response activated Cross priming refers to the DC that is required to fully activate T cells. The DC mediation here is important since DC is a professional APC, meaning it has crucial costimulatory molecules (e.g CD28, CD40) that the transplanted cell lacks - allowing the cell to fully activate the recipient T cells.

Anergy (unresponsiveness)

If the T cell recognizes a self antigen without costimulation, the T cell becomes unresponsive to the antigen because of a block in signalling from the TCR complex or engagement of inhibitory receptors signalling block may be the result of recruitment of phosphatases to the TCR complex or the activation of ubiquitin ligases that degrade signalling proteins. The T cell remains viable but is unable to respond to the self antigen.

Central B cell tolerance

Immature B cells that recognize self antigens in the bone marrow with high affinity either change their specificity or are deleted. 1. Receptor editing - If recognises self = RAG1 and RAG2 genes and initiate a new round of VJ recombination (See VDJ recombination) = VκJκ exon in the self-reactive immature B cell is deleted, and a new Ig light chain is expressed 2. Deletion = If editing fails, the immature B cells may dieby apoptosis. 3. Anergy = If developing B cells recognize self antigens weakly (e.g., if the antigen is soluble and does notcross-link many antigen receptors or if the B cell receptors recognize the antigen with low affinity), the cells become functionally unresponsive (anergic) and exit the bone marrow in this unresponsive state

Type I - IgE-mediated allergy

Immediate → symptoms appear within few minutes Environmental antigens = Allergenes (animal- & plant-derived / foods / drugs) Immune mechanism: IgE antibody, TH2 cells Mechanisms causing tissue injury: Mast cells, eosinophils, and their mediators (vaso-active-amines, lipid mediators, cytokines) - Most prevalent hypersensitivity - Can be dangerous if involves the airway or a systemic response

Antibodies (aka immunoglobulins) functions

Immune Proteins, secreted by B cells, that attach to antigens - Neutralization of microorganisms - Opsonisation and complement activation - ADCC = Antibody-dependent cell-mediated cytotoxicity - antibodies target infected cells for lysis by immune cells - Antibody mediated mast cell activation; e.g., against parasitic worms.

Pathogenesis diabetes 1

Immune-mediated destruction of the insulin-producing β cells of the islets of Langerhans in the pancreas because: Effector T cells recognize B-cell specific proteins → kills the β cell → no insulin production Islet antigens activate inflammation mediated by Th1 CTL-mediated lysis of islet cells Auto-antibodies against β cells, insulin, GAD, IA-2 β Auto-Abs against islet cells and insulin can be found in the blood of pts. In blood of relatives w/o DMT1 = predictive of its development * Local cytokine production damages beta production * Takes time for clinical onset because it takes time to destroy 90% of islets cells

Generation of monoclonal antibodies

Immunizing an animal with the desired antigen, collecting the serum and isolating the B cell with the desired antibody - Cell isolation harms it. Solved by fusion with Myeloma to form Hybridoma. - Nowadays recombination - antibody production by the use of viruses or yeast, rather than mice; Faster.

Hypo and hyper gammaglobulinemias

Immunodeficiencies due to altered activation of B and T cells: Hypo-gammaglobulinemias = low amount of Abs (selective isotype deficit) Hyper-gammaglobulinemias (X-linked, or recessive autosomal) = Hyper IgM syndrome *Many genes are involved in the activation of T and B cells and can be defective leading to IDs

Recombination by Inversion

In case the RSS are not found in the correct position (e.g. both found upstream of each V/J segment), the DNA is 'wrapped around' so that the 2 sequences become in the correct position. The DNA instead of being deleted from the genome, is moved into another position.

Influenza vaccine

Influenza Frequently undergo antigenetic shift and antigenetic drift. * Every year the vaccine is formulated according to the forecasting of the most 'prevalent' strains

3 mechanisms of immune evasion in intracellular bacteria

Inhibition of phagosome formation Some bacteria, e.g. MTB can inhibit processes that are vital for phagolysosome formation (fusion of the phagosome with the lysosome / decreasing of the luminal pH / activation of the enzymes) → the pathogens are not eliminated within phagocytes + not presented as antigens → they survive + proliferate Neutralization of ROS The pathogens express enzymes that target ROS and reduce their toxicity. This helps them both reduce the oxidative burst and its killing effects + deactivate non-oxidative microbicidal effectors induced by ROS Escape from phagosomes Some bacteria (e.g. Listeria monocytogenes) can break the phagosome membrane + reach the cytosole of the phagocyte.

classical pathway of complement activation

Initiated by the binding of C1 to antigen-complexed antibody molecules, which leads to the production of C3 and C5 convertases attached to the surfaces where the antibody was deposited. The C5 convertase cleaves C5 to begin the late steps of complement activation.

Innate T regulatory cells function

Innate Tregs recognize self-antigens, but are useful by inhibiting the activity of naive autoreactive T cells that 'escaped' the selection in the thymus (the first security layer). They work by producing IL-10 & TGF-β (anti-inflammatory / immunosuppressive cytokines), and physically competing with the escaped autoreactive T cells for the same antigens.

Bacterial evasion mechanisms

Intracellular and extracellular bacteria can evade the immune system by several mechanisms. - Usually this is a-symptomatic but can be dangerous after reactivation. Dangerous if - * Opportunistic pathogens that reside in the mucosa. They don't induce the adaptive response in healthy host, but in immunocompromised they can induce a threatening infection

Cooperation of CD4+and CD8+ T cells in defense againstintracellular microbes

Intracellular bacteria are phagocytosed by macrophages and may survive in phagosomes and escape into the cytoplasm. CD4+ T cells respond to class II MHC-associated peptide antigens derived from the intravesicular bacteria. These T cells produce IFN-γ, which activates macrophages to destroy the microbes in phagosomes. CD8+ T cells respond to class I-associated peptides derived from cytosolic antigens and kill the infected cells * This is a delayed response after the initial activation of Macrophages

Plasmodium immune evasion

Intracellular localization in RBCs and hepatocytes → sheltered from attack of extracellular immune mechanisms, e.g. antibodies. Complex life cycle + Antigenic variability - they frequently change antigenic expression (from phase to phase) so that antibodies produced against them are not efficient after a while. Parasites can escape the immune response. Even if the acute phase is fought off, some sporozoites can remain in the liver (where it's harder to get rid of them → chronic infection) and reinfect RBCs - reacutization of the disease.

Immune evasion of leishmania

Intracellular localization → sheltering from antibodies Induction of Th2 response instead of Th1 → bad for the body since Th1 is usually more effective.

Organisation of human Ig loci

L leader region V variable D diversity J joining C constant Enh Enhancer

T cell signaling downstream of PLCγ1 step 1

LAT adaptor protein that is phosphorylated on T cell activation binds the cytosolic enzyme PLCγ1, which is phosphorylated by ZAP-70 and activated. Active PLCγ1 hydrolyzes membrane PIP2 to generate IP3 - which stimulates an increase in cytosolic calcium, and DAG, which activates the enzyme PKC

Prevention and treatment of allergies

Lifestyle modification → if allergy is known - avoid exposure to allergens Once its triggered - difficult to turn it off Pharmacological treatments → most pursued strategy Desensitization → in order to change the Ab production against allergens (from IgE to IgG4) Exposure to increasing amounts of allergens to induce production of IgG4 so that mast cells & granulocytes won't degranulate (they'll have receptors for IgG instead of IgE) Not always effective + risks anaphylaxis

HIV structure

Lipid bilayer membrane w/ gp41 & gp120 = anchors through which the virus binds to: CD4 on T cells (& macrophages and DCs) and coreceptors CCR5 and CXCR4 A viral phospholipid envelope Enclosing the associated matrix ​(made o of p17) enclose a capsid (made of p24) which encloses: 2 copies of ssRNA Include 9 genes (partially overlapping), surrounded by long terminal repeats (LTRs) that aid the virus in integrating into the host cell's genome

Neoformed effector molecules

Lipid mediators - synthesized by an enzymatic reaction (= rapid) Leukotrienes / Platelet-activating factor Effect: chemotactic factors for leukocytes + amplification of lipid mediators production Cytokines & Chemokines - synthesized as consequence of gene expression activation TNFα / IL-4 / IL-13 Effect: stimulate & activate Th2-cell response IL-3 / IL-15 / GM-CSF Effect: promote eosinophil production and maturation CCL-3 Effect: a chemotactic factor for neutrophils and macrophages

The genetics of graft rejection (What is the most important locus involved in rejection?

MHC locus is the most important locus involved in rejection (A similar MHC results in acceptance of the grafts): Syngeneic grafts (donor & recipient are from the same identical strain) are not rejected A fully allogeneic graft (strain with MHC B donating to strain with MHC A) will be rejected. A graft from an inbred parental strain to its F1 offspring (MHC A x B) will not be rejected, since the graft is considered self by the host's lymphocytes. A graft from an MHC A x B donated to an MHC A mouse will be rejected, since it's not tolerant to the MHC B molecules which are seen as non-self. The MHC genes are responsible for transplant rejection/acceptance

Recognition of Alloantigens by T cells; direct recognition

MHC molecules displayed by cells in the graft are recognized by recipient T cells without a need for processing by host APCs [1-10% of T cells] * Although negative selection in the thymus efficiently eliminates T cells with high affinity for self MHC, it will not necessarily eliminate T cells that bind strongly to allogeneic MHC molecules - TCR genes have evolved to encode a receptor structure that has some intrinsic affinity for MHC molecules. - positive selection promotes survival of T cells with weak self MHC reactivity, and among these T cells, there may be many with strong reactivity to allogeneic MHC molecules

Induced T regulatory cells

Made in the periphery, becoming induced Tregs if in the 'right' environment - one rich in: - TGF-β - Molecules from bacterial metabolism, e.g.: Retinoic acid (obtained via Vitamin A metabolism - only done by bacteria) - Processed by DCs to induce FOXP3 - a specific TF in T cells. Short-chain fatty acids (product of bacterial fermentation. Can be absorbed by mucosa cells and used as a source of energy). * If the environment lacks retinoic acid and short chain FAs, but rather has pro-inflammatory cytokines (e.g. IL-6, IL-21, IL-23) → the naive T cells differentiate into Th17 (T helper 17), due to other TFs, like RORC & RORA

IgA

Main MucosAl antibody. 20% of serum - Babies receive IgA in breast milk; neutralise Ag in GI tract Valnce of 2 when a monomer and 4 as a dimer

Immunosuppresive drugs

Major categories of immunosprresive drugs are shown in the scheme along with their molecular targets. - inhibit or kill T lymphocytes.

V(D)J recombination

Mechanism that generates the ranges of B & T receptors. - recombination at any Ig or TCR locus involves selection of one V gene, one D segment (when present), and one J segment in each lymphocyte and rearrangement of these segments to form a single V(D)J exon that will code for the variable region (= Fab) of an antigen receptor protein (TCR / BCR). - Either heavy/Beta or Light chain rearrangements

Molecular mimicry in autoimmune diseases

Molecular mimicry can be when a foreign-antigen has striking similarities with self-antigens. --> Even if the immune system works properly (recognizes foreign antigens and elicits a proper immune response) it might accidentally (and 'legitimately') recognize a self-antigen with molecular mimicry to a foreign antigen and lead to detrimental effects for the body. - Streptococcus (maybe S. pyogenes) bacterial infection of the throat can lead to autoimmune cardiomyopathy due to similarities between bacterial antigens and the tricuspid valves.

T-DEPENDENT ANTIGEN (protein antigens)

Monovalent antigens = have only one copy of each epitope (→ 1 antigen can't simultaneously bind several BCRs) → they need the 'help' and interaction of T cells. * Within lymphatic tissues B cells (found in the follicles) interact with T cells (found in the paracortex):An antigen is presented by an APC / arrives freely through the lymph → T & B cells that can recognize it (via MHC / directly) move towards the boundary between the two zones.

immunity to parasites; Evasion of parasites

Most parasitic infections are chronic because of weak innate immunity and the ability of parasites to evade or resist elimination by adaptive immune responses. Furthermore, many anti-parasitic drugs are not effective at killing the organisms. Innate immunity evasion: Most parasites are adapted to evade immune defences. Principal defence against protozoa is phagocytosis but its readily evaded and some may replicate within a macrophage. Adaptive immunity evasion: high variety of protozoa and helminths = high variety of evading the adaptive response.

Severe combined immunodeficiency (SCID)

Most severe form of PID - the IS is so dysfunctional, it's almost considered absent Group of several diseases with common etiology: Mutations in variable genes that are important for either maturation or generation of B & T cells Genes often related to enzymes involved in the maturation/production of both T cells and B cells (e.g. RAG1, RAG2, DNA ligase 4, Artemis) → combined ID Transmission: Recessive / Dominant / X-linked Prognosis: very severe disease - almost surely lethal if untreated ☠️ ↑ susceptibility to infections, inc. opportunistic pathogens

Tumor Mechanisms to Evade the immune system

Most tumours are destroyed regularly by the IS; some evade. 3 mechanisms: 1. Inhibition of T cells by expressing inhibitory proteins - e.g: Expression of PD-L1 - binds to PD1 on CTLs → inhibits CTL activation Secretion of TGF-β (anti-inflammatory) → inhibits CTL activation 2. 'Failure' in producing tumor-specific or tumor-associated antigens - no foreign/signaling antigens = no recognition → grows with no disturbances. 3. Mutations on genes for antigen processing & presentation - if a cancer cell lacks MHC, it will be practically invisible to the IS → can thus grow undisturbed.

X scid

Mutation → T cell and NK cell maturation cannot occur No T cells = No T cell/B cell interaction → B cell malfunctioning *Similar clinical presentation for mutation in the gene responsible for Jak3 Kinase (directly a/w γC chain). This SCID is not X-linked Etiology: mutations to gene encoding for the common γ (γC) chain of cytokine receptors (common because it's common to IL-4, IL-7, IL-9, and IL-15 cytokine receptors). IL-15 & IL-17 → imp. for promoting maturation of NK cells & thymocytes

Examples of intracellular bacteria

Mycobacterium tuberculosis and Listeria monocytogenes

Gluten intolerance (Celiac disease)

Non-autoimmune condition affecting villus of small intestine. Not AI; caused by an immune response to gluten proteins (glutenin & gliadin), which contain mainly two proteins that are rich in glutamine and proline The proteins ↑ crunchiness & improve consistency of food like pasta → used more in industry → more celiac disease Involves mainly small intestine

immunosuppresive drugs mechanism; give example of 3 drugs

Normal T cell activation: TCR recognizes MHC → signal transmission that leads to activation & production of diff. Proteins:Example → Calcineurin binds to Ca2+ → calcineurin activates NFAT by dephosphorylation → activated NFAT can reach the nucleus + act as a TF → inducing gene expression and protein production ⇒ IL-2 production & T cell clonal expansion Immunosuppressive drugs target & interfere with this machinery: # Cyclosporine (CsA): binds to CyP and then to calcineurin → inhibiting it → NFAT can't be dephosphorylated & activated # Tacrolimus (FK-506): binds to FKBP → the formed complex blocks calcineurin. ⇒ both medications interfere with the signaling pathway and inhibit the ultimate effects. Tacrolimus is safer and less toxic. # Rapamycin (Sirolimus) (inhibitors of mTOR): binds FKBP which blocks mTORC1 → inhibiting the effects triggered by IL-2 (and IL-2R) [Easter island drug]. Blocks proliferation of cells and specifically lymphocytes. ⇒ it's less toxic, and preferentially used, however not always effective - may need combination with other drugs.

Hyperacute graft rejection

Occurrence: very quick - within several hours from transplantation Cause: pre-existing antibodies in the recipient (+ activated T cell clones) - The Abs may be natural (present in every patient) or patient-specific [induced by previous immunization (previous transplant/blood transfusion)]. - The pre-formed Abs attack the donor cells (circulating & non-circulating), especially the endothelial cells of the blood vessels → endothelial damage + activation of the complement system → underlying tissue exposed → activation of coagulation FXII (Hageman factor) → intrinsic pathway of coagulation activated → inflammation & thrombosis → occlusion of vessels or;→ detachment of a thrombus (⇒ embolus) that can occlude downstream vessels ⇒ ischemic necrosis of the graft.

Chronic graft rejection

Occurrence: within months/years It may occur after acute rejection or (usually) after a period of asymptomatic stages. Cause: minor histocompatibility antigens Instead of leading to immunological killing of the donor cells, fibrosis is developed in the transplanted organ. It's a chronic, low-intensity process involving thickening of the arterial walls of the vessels supplying the organ → partial/complete occlusion of the graft's vessels → Organ hypoxia → fibrosis forms in the parenchyma → organ insufficiency within years. Mechanism: The lymphocytes that recognize the alloantigens secrete cytokines that induce proliferation of the tunica media (muscle layer of the vessels) → thus the diameter of the vessel is decreased ↓ → blood flow to surrounding parenchyma is reduced ↓ → fibrosis in the parenchyma (due to progressive hypoxia) Not yet solvable - the most common long-term consequence of organ transplant.

Acute graft rejection

Occurrence: within weeks (2+) Cause: presence of allogeneic MHC molecules within the graft. It's slower since it requires activation of T lymphocytes against allogeneic MHC expressed on the surface of endothelia / other cells of transplant → damage of vascular endothelium → coagulation + damage to transplanted tissue. Alloantibodies against MHC molecules can also cause graft rejection The alloantibodies are targeted by TCR/Antibodies leading to similar consequences (via different mechanisms - classical complement activation) Specific antibodies reveal the presence of C4d in the capillaries (proving complement and C4 activation) Used to be very problematic, but nowadays it's overcome.

Mast cells, vs Basophils vs. Eosinophils

Order of importance: Mast cells > Basophils > Eosinophils Mast cells = resident cells | Basophils & Eosinophils = circulating cells FcεRI - highly expressed on mast cells + basophils - less on eosinophils.

Preformed effectors of mast cells and basophils

PREFORMED Mediators (stored in cytoplasmic granules): Enzymes Tryptase / Chymase / Cathepsin G / Carboxypeptidase Effect: remodeling of the connective tissue matrix Vasoactive mediators Histamine / Heparin Effect: induce vasodilation + smooth muscle contraction (heparin) + increase vascular permeability - Cytokines increase - Preformed TNFα Effect: promote inflammation + stimulates cytokine production in many cell types + activates the endothelium

Eosinophiles preformed and neoformed effectors

PREFORMED mediators: Enzymes Eosinophil peroxidase Effect: catalyzes halogenation → toxic to parasites & mammalian cells + induces release of histamine from mast cells Eosinophil collagenaseEffect: : remodeling of the connective tissue matrix Toxic proteins Major basic protein (MBP)Effect: toxic to parasites & mammalian cells + induces release of histamine from mast cells Eosinophil cationic protein = a neurotoxin → toxic to parasites Eosinophil-derived neurotoxin NEOFORMED Mediators: Cytokines & Chemokines (by gene expression activation) IL-3 / IL-5 / GM-CSF CXCL6 Lipid mediators (synthesized enzymatically) Leukotrienes / PAF

Primary vs. secondary immunodeficiency

PRIMARY ID Causative abnormality may be in: Components of the innate IS Different stages of lymphocyte development Responses of mature lymphocytes to antigenic stimulation - Generally identified due to a clinical history of repeated infections * >400 syndromes known (so far) - many are very rare Generally - the more severe - the more rare they are SECONDARY ID Causative abnormalities are acquired during life, following other pathologies, treatments, or infections, e.g: - Flu / Denutrition - transient state of ID - HIV - causes AIDS

Parasites

PROTOZOANS = unicellular eukaryotes. Examples: Plasmodium Leishmania Trypanosoma Entamoeba histolytica METAZOANS = pluricellular eukaryotes. Examples [both of the flatworm (platyhelminthes family)]: Schistosoma Filaria * may be more difficult to treat since they are eukaryotes that adapted a lot throughout evolution ⇒ often end up as a chronic infection

follicular helper T cells (Tfh) and its generation.

Play several important roles in the activation and differentiation of B cells in the germinal centre reaction - T helper --> Tfh generation: sequential interactions by Apc then B cells, in the paracortex. A - 1st interaction with TCR that induces migration (Via chemokines) to the paracortex. B - ICOS (on Th) and its ligand ICOSL (on B) → induce expression of TF Bcl-6 → mediates the differentiation into a Tfh cell that can enter the follicle * Once Tfh is in the follicle; it can stimulate further signalling on a B cell that is required in the Germinal Centre reaction.

Poliovirus vaccine

Poliovirus causes Poliomyelitis (fecal-oral transmission). Effects: 91-96% of cases → asymptomatic infection 4-8% of cases → paucisymptomatic infection 1% of cases → permanent paralysis Mortality in 5-15% of cases Still present in Nigeria, Pakistan, Afghanistan Vaccines: Sabin Vaccine More effective than the IPV An Attenuated virus = OPV (Oral Polio Vaccine) Oral administration → mimics the natural poliovirus infection → more effective Risk: could reverse (become) pathogenic & virulent (esp. Strain 3)→ today the risk-benefit ratio does not justify the use of this vaccine

Thymus dependent antigens vs. thymus independent antigens

Polysaccharide and lipid antigens are considered thymus-independent antigens Can activate B cells without intervention of T cells The response is rapid, but relatively simple (mostly via low-affinity IgM Abs) Protein antigens are considered thymus-dependent antigens Require the intervention of [helper] T cells to obtain an efficient B cell activation The response is slower but more powerful and ''sophisticated''.

Negative and positive selection mechanisms of T cells

Positive selection - Low Affinity recognition of the MHC molecule (not the antigen; signalling self-molecules) → ensures the T cells survive and mature. High Affinity recognition of a self-antigen can bring to differentiation of the T cell into Innate T regulatory cells (agonistic selection) that can suppress T cells (in the periphery, for the same self-antigen) that escape negative selection in the thymus. Negative selection - Very High-affinity recognition of the MHC+self antigen complex → cells undergo apoptosis [to prevent auto-reactive cells from reaching the periphery and attacking our body cells (autoimmunity). If they ​do not recognize​ the (self-antigen + MHC) complex at all (even not the MHC, meaning they won't be able to identify self-cells) →apoptosis

Positive and negative phases of lymphocyte maturation

Positive selection - ensures maturation of T cells whose receptors bind weakly to self-MHC Negative selection - eliminates developing lymphocytes whose antigen binds strongly to self antigens present in the lymphoid organs

Ligand-receptor pairs involved in T cell activation (Positive and negative modulations)

Positive: CD3 - signal transduction by TCR complex ζ - Signal transductionby TCR complex CD4 - Binds MHC2 that is expressed on antigen presenting cells, involved in signal transduction CD8 - MHC1 (all nucleated cells ) CD28 - Expressed in APc; Signal transduction Negative: CTLA-4 PD-1 LFA-1: Binds ICAM

Development of B cells from a pluripotent stem cell

Pro B --> FO B --> MZ B --> B-1B. FO B → follicular B lymphocytes; circulate in the lymph, responsible for generating the antibodies toward protein antigen (T dependent) MZ B → marginal zone B lymphocytes; circulating in the spleen, having a rapid response toward blood-borne antigens B-1B → found on tissues and epithelia; responsible for the generation of IgM and IgA, the natural antibodies against bacterial antigens

3 phases of lymphocyte maturation

Proliferation phase - the maturation depends on availability of growth factors Pre-lymphocyte phase - it starts to express an antigen Selection phase - immature lymphocytes are exposed to self-antigens so they can develop tolerance towards them: Positive and negative phases

3 stages of lymphocytes maturation

Proliferation phase - the maturation depends on availability of growth factors Pre-lymphocyte phase - it starts to express an antigen Selection phase - immature lymphocytes are exposed to self-antigens so they can develop tolerance towards them: Positive and negative phases

Selective Deficit of IgA

Quite frequent (1:700 in Caucasians) Since survival rates are high, and many people don't even know they have it → they have children normally, w/o regarding it Transmission: Recessive / Dominant Effects Low IgA concentration in blood (IgA <50 mg/ml) Phenotypic variability: from totally asymptomatic to occasional respiratory infections to even quite severe cases Treatment: not really provided

Prevention of haemolytic disease of the newborn

RHOGAM (very old drug; an anti-RhD IgG) at week 28 of pregnancy + soon after delivery to avoid sensitization. Why does it work? It provides passive immunity to the mother avoiding activation of plasma cells and development of memory cells. - Mother don't produce memory cells against foetal blood - If the mother already has memory cells - Intravenous Contra-Ab-IgG is administered. - Inducing early birth and expose newborn to blue light

RAG1 and RAG2

Recombination Activating Genes cut the DNA at the RSS ↑

Suppression as a mechanism of peripheral tolerance

Regulatory T cells: can recognize self-antigens → induce production of immunomodulatory cytokines → they turn off the immune response & block T cell activation - Innate Tregs are produced within the thymus, via AGONISTIC SELECTION:Immature T cells that have a high-affinity to self-antigens, instead of getting killed by apoptosis, become Tregs that can go to the periphery and produce modulatory cytokines to control the immune response

Mitochondrial relation to T cell activation

Resting T cells mostly use oxidative phosphorylation for their energy expenditure. Proliferating T cells (after activation) switch to anaerobic glycolysis - it generates less energy; but preserves & produces the building blocks for cellular organelle biosynthesis - required for cell proliferation + functional responses.

SCID involved mutations of genes involved in somatic recombination of TCR & BCR

SCID caused by mutations in recombination-activating genes - RAG1 & RAG2, which are important in the rearrangement and recombination of the genes encoding for Ig and TCR.They're only expressed in developing lymphocytes, and are essential to T & B cell maturation, together with Artemis and DNA-PKcs. - Mutations are rare - Mutations → complete absence of T & B cells (= catastrophic)

T cell signaling downstream of PLCγ1 step 3

STIM1 induces the opening of the CRAC channel that facilitates entry of extracellular calcium into the cytosol. Orai is a component of the CRAC channel. Increased cytosolic calcium together with PKC activate various transcription factors, leading to cellular responses. DAG, diacylglycerol; IP3, inositol 1,4,5-trisphosphate; PIP2, phosphatidylinositol bisphosphate; PKC, protein kinase C.

Schistosoma

Schistosoma Mansoni parasites (flatworm family) cause Schistosomiasis 1. A certain Snail acts as a vector for Schistosoma parasites to humans: 2. Sporocytes can be found in snails that are in some waters. Within the snails, the sporocytes transform into cercariae → free-swimming, infective 3. Cercariae can easily penetrate an intact skin → they lose their tails ⇒ become schistosomulae 4. Schistosomulae enter the bloodstream → reach the portal blood of the liver 5. Within the liver, they mature into their adult form → female & male adult worms pair up → reach the mesenteric venules of the bowl → to perform sexual reproduction → lay eggs that are expelled in stools → dissipate in water and the cycle restarts.

Regulation of B cells through FcγRIIB (CD32)

Secreted antibodies inhibit continuing B cell activation by forming antigen-antibody complexes that simultaneously bind to antigen receptors and inhibitory Fcγ receptors on antigen-specific B cells - B cell (normal) activation: BCR binds to its specific antigen → signalling cascade ultimately leads to the generation of phosphatidylinositol-3-phosphate (PIP3) → induces activation of downstream molecules which are required for complete B cell activation. - IgG interferes with this activating signaling cascade: It forms antigen-antibody complexes that binds 2 places, simultaneously: Via the antigen - binds to the BCR Via the Fc portion of the IgG - binds to the inhibitory receptor FcγRIIB(CD32)

C (constant) region

Segments located at the 3' end of J segments coding for the constant heavy region of the heavy chain, determining the isotype and subtype Each locus has a different number of C region genes: The K light chain locus has a single C gene; The 𝛌 light chain locus has 4 C genes; The H chain locus has 9 C genes that encode for the 9 different Ig isotypes and subtypes.

T cells development includes

Sequential rearrangement and expression of TCR genes Cell proliferation Antigen induced selection Commitment to phenotypically andfunctionally distinct subsets

Graft vs. Host Disease (GVHD)

Serious complication of bone marrow transplant (graft). Immune cells from the donor bone marrow attack the recipient's (host's) tissues. - happens when the donor & recipient do not share all MHC loci. * mature T cells have already undergone tolerance in the BM and Thymus of the donor's body, and haven't learned to recognize the recipients cells. - A form of the disease can occur due to minor antigens → even if they are HLA-identical, peptides deriving from Y-linked antigens (SMCY protein), or other antigens expressed in autosomal genes (not tolerated by the donor's minor histocompatibility loci) may lead to disease. Milder GVHD, but still present.

IgD

Signals maturation of B cells

Epitope

Small, accessible portion of an antigen that can be recognized. Big molecules can have more than one epitope multi/polyvalent → repeated epitopes that activates B cells through the clusterization of B cells conformational epitopes → lost when denaturated linear epitopes → can be inaccessible due to folding

How can our relatively small genome encode for a immense variety of antigen receptors?

Somatic recombination

epidemiology diabetes 1

Some studies show: DMT1 may be preceded by viral infections (e.g. coxsackievirus B4): the inflammation, cell injury, and expression of costimulators may trigger an autoimmune response, because the virus expresses molecules that resemble the ones attacked by the auto-Abs → breach in self-resistance Epidemiological data suggests: Repeated infections actually protect against DMT1. Theory - more control of infectious disease in developed countries → ↑ DMT1

3 mechanisms of immune evasion in extracellular bacteria

Surface immunomodulation The pathogens avoid immune detection by secreting immunomodulators from infected cells so that their own surface molecules and ligands are modified. Some viruses and bacteria (e.g. Salmonella, Neisseria, Yersinia) can alter agonists on their surfaces (e.g. Lipid A, Flagella, peptidoglycan) to avoid TLR4 detection Antigen Variation Fights the adaptive immune response by changing the recombination of its surface determinants:- Opacity (Opa) outer mb proteins → govern bacterial adhesion + uptake into host cell | 11 recognized- Lipo-oligosaccharide (LOS) → outer mb component involved in host interactions | 12 recognized- Type IV Pilus (Tfp) → cellular adherence→ The different Opa proteins & LOS immune types can be turned on and off → forming diff. combin. Vesicle formation Pathogens create vesicles that contain receptor antigens → secrete them → antibodies bind to them instead of to the actual bacteria!

Examples of autoimmune diseases caused by type 3 hypersensitivity

Systemic Lupus Erythematosus (SLE) Post-streptococcal glomerulonephritis = Kidney disorders; post infection.

Type 4 hypersensitivity

T cell mediated, Delayed (AKA delayed hypersensitivity) → Symptoms appear within days (>12 hrs, maximum 48-72 hours to recruit Th1 to site of exposure and see a reaction) - Particularly involve T lymphocytes - Related diseases: Non-autoimmune: delayed type hypersensitivity (DTH), contact hypersensitivity, IBD, gluten intolerance (Celiac disease) Autoimmune: rheumatoid arthritis, multiple sclerosis, type I diabetes, psoriasis

T lymphocyte tolerance (DC4+)

T helper cells are necessary inducers of cell-mediated and humoral immune responses; therefore T cell tolerance is highly effective. Central T cell tolerance (negative selection) - if during maturation T cells recognise self antigens with high avidity they are deleted. - Positive selection of T cells is possible; these cells are not deleted but develop into regulatory T cells. - The regulatory cells leave the thymus and inhibit responses against self antigens in the periphery. What determines the choice between deletion and development of regulatory T cells is not known

CCR7 effect on migration of T helper and B cells

T helper cells: ↓ expression of CCR7 + ↑ expression of CXCR5 (binds CXCL13 - abundant in the follicle) → T cell moves towards the follicle. B cells: ↑ expression of CCR7 [binds CCL19 & CCL21 - abundant in the paracortex → B cells move towards the paracortex (outside of the follicles)]

Acute GVHD

Targets; epithelial cells, skin, gut, liver Can be fatal - main cause of mortality in these patients Involves: NK cells, CTL CD8+, cytokines Therapy: Anti-T lymphocytes antibodies that can help get rid of mature T cells in the graft (that can still exist even after analysing the pool of transplanted stem cells). These Abs could be taken from an animal serum (one that has been sensitized against T cells of humans). Monoclonal antibodies - a bit more advanced.Once used against CD3 molecules (part of the T cell receptor), but they're toxic → not used anymore.

Chronic GVHD

Targets; skin, gut, lungs In this case, the attacking graft cells don't induce killing of rapidly-dividing cells, instead pro-inflammatory cytokines produced → make them undergo atrophic fibrosis by deposition of collagen fibers (substitutes the parenchyma). Therapy: Transfer of autologous T regulatory cells - Tregs can control the alloreactive immune response ⇒ delaying GVHD / preventing death. Tregs are taken from the patient → activated → cloned in vitro → re-administered. anti-TNF Abs treatment (also used in rheumatoid arthritis) Corticosteroids (e.g. prednisone / other synthetic corticosteroids) - heavy therapy, not completely effective (only targets 1 possible mechanism) iPSCs(Induced Pluripotent Stem Cells) from the recipient - future therapy

Processes within a germinal centre

Th present the antigen to a B cell → which is activated → migrates into the germinal center's dark zone → proliferates WITHIN THE FOLLICLE: The small non-dividing progeny of B cells migrate to the adjacent light zone → they come in contact with the abundant FDC as well as TFH cells and subsequent selection events occur. - Only B cells with the highest affinity Ig receptors ("the fittest") survive and eventually differentiate into: Plasma cells - long-living | can produce any Ig | can stay in the follicle or move into the BM Memory B cells - recirculate into the lymph | if they encounter the antigen that activated them → give rise to the same reaction

Th1 and Th17

Th1 → produces IFN​γ → promotes inflammation + makes it easier for the cell to get rid of pathogens. Th17 → produces cytokines, e.g. IL-17 → activates neutrophils. # The Vaccine against Clostridium tetani is an inactivated tetanus toxin (tetanospasmin)

B Cell Receptor (BCR)

The BCR is quite similar to the TCR in shape and function, but different since it can directly recognize an antigen, without the need of its presentation via MHC molecules. It's formed of a membrane IgM (or IgD), associated with Igα and Igβ chain molecules (analogous to CD3 & ​ζ-chains of the TCR) Function: transmit the signal to the cytoplasm via their ITAM sequences --> stimulation of transcription factors

CD4 vs CD8 receptors

The CD4 protein is an integral membrane monomer consisting of four extracellular Ig domains, a transmembrane domain, and a cytoplasmic tail. * bind the beta2 domain of MHC class II molecules The CD8 protein is either a disulfide-linked αβ integral membrane heterodimer or a disulfide linked αα homodime * bind alpha3 domain of MHC class I molecules ** Both bind LCK

Germinal centre

The characteristic events of helper T cell-dependent antibody responses, including affinity maturation, isotype switching, and generation of long-lived plasma cells and memory B cells ( = Germinal centre reactions), occur primarily in organized structures called germinal centres that are created within lymphoid follicles during T-dependent immune responses. - develop about 4 to 7 days after the initiation of a T-dependent B cell response - 3 zones - Dark zones (Intense proliferations of many B cells) and mantle zones (Naive B cells)

Symptoms of GVHD

The disease mainly acts on tissues with a high replication rate. Symptoms mainly related to skin (→ rash/erythroderma), gut (→ diarrhea) and liver (→ serum bilirubin)

Immunogenetics; chromosomes

The locus of the heavy chain is on chromosome 14 The light chain contain different loci for the κ and λ; respectively chromosomes 2 and 22 * genes that encode the diverse antigen receptors of B and T cells are generated by the rearrangement in individual lymphocytes of different regions of the genetic loci for heavy and light chains.

Recombination by Deletion

The non-conservative 12 / 23 nucleotides are not random. 12 bp corresponds to a single complete turn of the DNA helix, while 23 bp corresponds to 2 turns ⇒ they are close, and can become united by the RAG1 & RAG2 complex, which cuts the DNA so that a circular DNA is cut out and lost. - Before the circular DNA is lost - if it's found in the cytoplasm = marker of a newly-recombined cell.

importance of thymus as the site of T cell maturation

The thymus is the major site of maturation of T cells - If the thymus is removed from a neonatal mouse, this animal fails to develop mature T cells - T lymphocytes migrate to thymus after hematopoiesis (PRO-T stage)

INHERITED IMMUNODEFICIENCIES

There are plenty, the most important ones are related to genetic defects that are dominant, recessive, or X-linked.

Development of T-regulatory cells (Treg)

These cells express mainly CD4 and not TCR but producing modulators cytokines (and not activatory). - Specialised in inhibiting the immune response

Deficiencies in C2, C3, C4

Too little of 1 or more complement proteins OR don't function properly → underactive immune response: More frequent infections Worsening of autoimmune disease Because small immune complexes are not opsonized + don't get picked up by circulating immune cells C2 deficiency → mo C3 deficiency → severe clinical manifestations Since C3 is needed in large quantities + involved in all pathways C3 plays a central role in phagocytosis & MAC formation C4 deficiency → less significant problems Since C4 is needed in small quantities C4 can continue its role in activating other proteins

Allotransplant

Transplantation of cells, tissues, or organs, to a recipient from a (genetically non-identical) donor of the same species

Tubercoloid vs. lepromatous

Tubercoloid: granulomas that form around nerves and produce peripheral sensory nerve defects and secondary traumatic skin lesions but with less tissue destruction & a bit of bacteria in the lesions. Possible due to production of IFN-γ & IL-2 in lesions Lepromatous: Mycobacteria proliferate within macrophages and are detectable in large numbers. The bacterial growth and persistent but inadequate macrophage activation result in destructive lesions in the skin and underlying tissue. differences may be due to different patterns of T cell differentiation and cytokine production in individuals (written above) that are influenced by our genome settings * Th1 - Type 1 cytokines (e.g. IL-2, TNF-β, IFN-γ) → resistance to infectionSeen in TUBERCULOID Leprosy * Th2 - Type 2 cytokines(e.g. IL-4, , IL-5, IL-10) → progressive diseaseSeen in LEPROMATOUS Leprosy

Diseases with no efficient vaccines available

Tuberculosis is in the list even though the BCG vaccine has been in use for many years. This is because it's efficacy is only ~50% HIV/AIDS - perhaps the most important missing, even though there's been an incredible effort to crack this challenge. Measles (Morbillo) - exists, but the anti-vax campaign dramatically reduced the vaccination rate. Another problem of this vaccine is its heat-sensitivity → requires proper refrigeration → limiting its use in tropical countries.

5 types of hyper IgM sydrome

Type 1: X-linked Mutations in CD40LG gene T cells can't communicate to B cells to switch class Type 2: autosomal recessive Mutations in the AICDA gene B cells cannot recombine genetic material to change heavy chain production Type 3: Mutations in CD40 gene B cells can't receive the signal from T cells to switch class Type 4: Defect in CSR downstream of AICDA that doesn't impair somatic hypermutation Type 5: Mutations in the UNG gene Rare X-linked type (recently discovered) NEMO mutation (affects the NF-𝝹B pathway).

4 types of hypersensitivity

Type I (immediate, IgE) = Classical allergy Type II (hours, cytotoxic) - IGg, & IgM, autoreactive. Type III (hours, immune complex-mediated) - Im-comp travel in the circulation until they precipitate ectopically, Causing inflammation and damage Type IV (days. delayed, not considered allergy bs no Ab) - No or partial involvement of Ab. Reactions to contact materials such as vegetable oils (like that of Poison Ivy) or metals (e.g. Nichel) they penetrate through our barriers (mostly the skin) -> alter the structure of self-peptides -> prompt a response by T cells

Pathogenesis of multiple sclerosis

Unknown trigger sets an initial focus of inflammation in the brain → BBB becomes locally permeable to leukocytes & blood proteins In genetically susceptible individuals (HLA susceptibility) - T-cells specific for CNS antigens (that have been activated in peripheral lymphoid tissue) reencounter the antigen presented on microglia/DC in the brain → inflammatory reaction w/ mast cells, complement activation, Abs, and cytokines ⇒ demyelination of neurons

T cell activation

Upon an interaction between APC & a T cell (CD8+/CD4+) The CD8+/CD4+ coreceptor (whichever) is bound to Lck (Lymphocyte-specific protein tyrosine kinase): - Lck is found on a lipid raft (they move less, allowing a longer-lasting, reliable interaction → increasing the efficiency in signal transmission). - It can phosphorylate the activated ITAM sequences (on CD3 & ζ chains) on their Tyr res.⇒ ITAM creates conformational change in the whole TCR → activated Phosphorylated Tyr residues act as anchors for other adaptor proteins e.g., ZAP-70

Early tyrosine phosphorylation events in T cell activation

Upon antigen recognition: A. clustering of TCR complexes with coreceptors (CD4 or CD8) - Lck becomes active and phosphorylates tyrosines in the ITAMs of CD3 and ζ chains B. ZAP-70 binds to the phosphotyrosines of the ζ chains and is itself phosphorylated and activated. ZAP-70 activates many adaptor moluceles such as LAT. C. Adaptors activate exchange factors (AKA signalosome) such as PLCγ1 --> Activation of RAS and other small G proteins. = Activation of many cellular responses. * The final role is clonal expansion, differentiation, and effector function.

Organisation of human TCR loci

Very similar to the Ig loci (LVDJCEnh) except some differences in the C fragments: main difference between Ig loci and these TCR loci is that the latter have very few C segments:

Viruses; Virions

Viruses = small, obligate, intracellular parasites with a (ss/ds |circular/linear | monopartite/multipartite) DNA/RNA genome, surrounded by a protective protein coat (capsid). Virion = the viral genome and its capsid. Goal of the virus: to deliver its genome into the host cell, in order to use the cell machinery, so that its genome can be expressed.

Immune senescence

With ageing, there is increased dysfunction of both innate and adaptive immune responses, which contributes to impaired immune responses to pathogens and greater mortality and morbidity. - These population will benefit most from vaccines - there's a positive correlation between age and pro-inflammatory molecules (e.g. CRP, IL-6, IL-15, IL-18), while IL-10 is negatively correlated

Agammaglobulinemia

X-linked agammaglobulinemia (XLA) The causative mutation affects Bruton's tyrosine kinase (BTK) - a specific tyrosine kinase involved in B cell development: BTK Functions: Mediator of the BCR signaling pathway in mature B cells Pre B cell maturation In this level, the BCR is not yet developed - its precursor - pre-BCR is found. Pre-BCR maturation is a checkpoint for the pre B cell maturation. Several tyrosine kinase proteins, including BTK, have to bind the pre-BCR to 'check all is well'. If one cannot bind → there's negative selection of the pre B cell that instead of continuing with maturation, gets killed/inactivated. Pre B cells that lack BTK are negatively selected In XLA, BTK lacks → no maturation of B cells!

Chronic granulomatous disease

X-linked mutation affecting NADPH oxidase causing dtysfunctioning neutrophils and oxidative burst - 80% in males - ⅓ - de novo mutations vs. ⅔ of cases - mutations in the gp91 gene - Physiopathology: Defective phagocyte NADPH oxidase → insufficient production of ROS ⇒ the phagocytes (e.g. neutrophils, monocytes, macrophages) cannot destroy certain microbes → they remain within the phagosome or lead to the death of the cell → recruitment of more macrophages → granuloma formation Susceptibility to bacteria that are already prone to stay within the phagosome, e.g. MTB

T cell signaling downstream of PLCγ1 (Role of PLCγ1 in the signalosome)

a phospholipase able to cut PIP2 into DAG and IP3

hyperimmune serum & COVID

a special preparation obtained from human donor polls selected for high antibody against a specific disease - Taking plasma for generation of Ab from recovered patients is problematic (A. of blood, not necessarily effective) - Monoclonal Ab can be a solution: creating antibodies to identify the spike antigen of Sars-Cov-2.

Immunological tolerance

a state of unresponsiveness of the immune system to substances or tissue that have the capacity to elicit an immune response - Antigens that induce tolerance = tolerogens, different from immunogens, which generate immunity - Central tolerance is the main way the immune system learns to discriminate self from non-self. Peripheral tolerance is key to preventing over-reactivity of the immune system to various environmental entities

Allergy (AKA Atopy)

abnormal immediate hypersensitivity acquired by exposure to an antigen - a prototypic type 2 inflammatory disease - E.g., Food allergy Allergenes: nuts, peanuts, milk, eggs, fish, shellfish, soy, cereals Entry route: Ingested (oral) → GI reactions → absorbed → systemic responses

Ab distribution

about 80% is IgG, 15% is IgA, 5% is IgM, 0.2% is IgD, and a trace is IgE

Graves disease

an autoimmune disorder that is caused by hyperthyroidism and is characterized by goiter and/or exophthalmos * Anti-TSH receptor Abs bind to the TSHr and act as agonists → continuous inappropriate release of T3 & T4 (w/o regulation of TSH) ⇒ hyperthyroidism * Removal of thyroid; Hormone replacement therapy; Steroids.

Monoclonal antibodies (MoAb)

antibody produced from a cell line made by cloning a unique white blood cell. All subsequent antibodies derived this way trace back to a unique parent cell. - have monovalent affinity, binding only to the same epitope

Immune complexes

antigen bound to Ab; 3 zones. - If equivalent concentration → large → more likely to precipitate - If excess ab or ag → small →harder to dispose If not disposed and precipitate - Lupus & Serum sickness disease → due to serum sickness

Multivalent antigens (T-independent antigens)

antigen with multiple copies of the same epitope; simultaneously interact (cross link) with several BCRs 1. Cross-linking → Src family kinases are recruited up to a physical interaction between them and the BCR → they phosphorylate the tyr residues on the Igα and Igβ ITAM sequences → the P-ITAMs trigger subsequent downstream reactions. 2. Co-stimulation for activation of the intracellular cascade and TFS is provided by TLR (E.g, 5,7,9) or a trimer that is composed of cd81, cd19, cr2.

J (joining) chain

around 6 genes; undergoes recombination, tens of thousands of combinations are possible - polypeptide that stabilizes IgA dimers, IgM pentamers

Fc receptors

bind Fc region of antibodies help NK and macrophages to phagocyte and kill target cells.

polyclonal antibodies

bind to multiple epitopes and are usually made by several different antibody-secreting plasma cell lineages. (Derived from more than one cell line)

Leishmania

cause Visceral / Cutaneous Leishmaniasis Sandflies act as vectors for leishmania parasites to humans:The sandfly sucks on the human for blood, whilst injecting the parasites in the promastigote form. The promastigotes are ingested by macrophages → reproduce and transform into amastigotes within them → secreted by 'rupturing' the macrophages → go on to infect and multiply in other cells (many tissues, but also macrophages) Amastigotes enter the bloodstream → where, if bitten again, the sandlfy might pick up (and 'convert' them back into promastigotes → reproduce → migrate to proboscis

Isotype switching; what factors induce what change? where does it occurs?

ccurs in the light zone of the germinal center in the lymph nodes. IFN-γ → induces class switching to IgG1 and IgG3 IL-4 → induces class switching to IgE and IgG4 TGF-βl APRIL, BAFF & others → induce class switching to IgA

Deletion as a mechanism of peripheral tolerance

cells with a high-affinity to self-antigens / or that are repeatedly stimulated by the same antigen (implying this antigen may be a self-molecule) → die by apoptosis Two types of apoptosis: 1. Mitochondrial (intrinsic) pathway:The Bcl-2 protein family (mainly BH3-only) sense cell stress (strongly activated by T cells) → lead to mitochondrial leakage (e.g. cytochrome C) → activate caspases → lead to cell death 2. Death receptor (extrinsic) pathway:Repeated stimulation of T cells → leads to expression of Fasdeath receptors on their surface. Once Fas binds to a Fas-Ligand on another cell → activates caspases → cell death

V variable part

cluster of genes positioned at the 5' end; the amount of functional genes vary according to the loci and species (40-100)

fetal erythroblastosis

condition in which antibodies from a Rh- mother attack the RBC of a Rh+ fetus - If the mother is Rh- and the fetus is Rh+ → the mother develops anti-RhD Abs after delivery (upon massive contact with baby's blood). This is fine, unless the mother encounters Rh+ again, like in a following pregnancy. Then, if the fetus is indeed Rh+ → the antigen will be recognized as non-self → IgG from the mother crosses the placental barrier and attacks the fetus. - 72h before delivery (the 1st one) mom is administered with anti-Rh antibody to prevent.

Discovery of the complement system

discovered by seeing that bacteria were degraded in normal serum, but when the serum was heated they were not. Since antibodies don't denature when heated, they figured there must be another element that is damaged upon heating, and affects bacterial degradation

Infections diseases

diseases caused by bacteria, viruses, fungi, parasites; does not refer to degenerative or genetic diseases or abnormalities Started with the history of civilizations; increased spread with the growth of the communities. Smallpox - one of the main pathologies in humankind. Clues from ancient china where they took smallpox materials from scars of infected people and used it to inoculate (an antique form of vaccine) Many plagues have struck Europe and the world. One caused by the Yersinia Pestis bacteria.

Superantigens

enhance the binding of any peptide to a certain type of T cell (those with a variable β3 domain - TCR Vβ3 is 2% of all T cells) ⇒ cytokine storm that can be lethal to the patients, since over-activation of T cells lead to their death (tolerance mechanism) - paralyzes the immune system so that it cannot fight the real threat. - done by binding to the TCR and MHC I molecule. - It's like keeping our immune system busy and distracted, to overwhelm it, so that it cannot deal with the real problem. - Common in some staphyloccoci infections

Complementary determining region

finds epitope, a hypervariable region located in an Ab that determines the Ag- Binding specificity of the Ab

IgM

first antibody produced; 0.2%. - Doesn't need T cell for activation - Increased Valence once secreted from 2 to 10; once secreted there is a total of 5 Ab - Most effective in activating the complement pathway

T cell activation; receptors that need an adaptor protein

for TCR - Cytosolic tail is too short - Adaptor protein is needed. * utilise kinases as adaptor proteins -> phosphorylation of tyrosines in their intracellular domain (TCRs) --> can have kinase domains in their intracellular domain enabling the phosphorylation of tyrosine residues in the tail (c-kit)

HAART

highly active antiretroviral therapy- use of combinations of drugs that are effective against AIDS * Latency phase is maintained and prolonged * Inhibit every step

Th17

important for pathogen clearance in mucosal barriers. They produce IL-22 and IL-17, which recruit neutrophils to the site of inflammation. They can also activate the gut epithelium to fight invading bacteria.

Is VDJ error prone?

inherently error prone, because even if two cells use the same rearrangement for the same chain, it's highly likely that one of them would be affected by the enzyme terminal deoxynucleotide transferase (TdT) that randomly adds & removes nucleotides (that are then joined by DNA ligase IV) ⇒ the cells would differ in their antigen specificity.

Sequence of events in immediate hypersensitivity (Allergy/ Atopy)

initiated by the introduction of an allergen, which stimulates IL-4 producing helper T cell responses and IgE production. IgE sensitizes mast cells by binding to FcεRI, and subsequent exposure to the allergen activates the mast cells to secrete the mediators that are responsible for the pathologic reactions of immediate hypersensitivity.

Smallpox vaccine

injection of live vaccinia viruses that cause antibodies and memory cells that work against smallpox viruses

Germinal centre reaction generation

interaction between 3 types of cells (follicular DC, germinal center B cell, Tfh) gives rise to the... Sequential activation is done first by DCs and then by B cells: A - Strong TCR activation by dendritic cells: Bcl-6 expression, low levels of the α chain of the IL-2 receptor (IL-2R) on CD4+ T cells: Prevents transformation into Th1, Th2, Th17. B - The nascent Tfh cell completes its activation via B cells, through the TCR and other costimulatory molecules C - The Tfh then provides the B cell with further signaling via cytokines, e.g. IL-21, IL-4, IFN-γ

Mantoux test

intradermal test to determine tuberculin sensitivity based on a positive reaction where the area around the test site becomes red and swollen Negative: bubble shrinks and the dimension of the circular 'lesion' is <5mmThis means that the patient's T cells haven't recognized the proteins as a threat - the patient was not exposed to TB before. Positive: the bubble has increased in size + indurated

Pathological immunological tolerance

lead to autoimmune situations and diseases

L (leader) region

located at the 5' end of the V segment; encodes for N terminal residues called leader (for signal) peptides Is responsible for guiding newly synthesized nucleotides into the ER lumen and later are cleaved

RNA vaccines & their possible disadvantages

mRNA instability: naked mRNA is quickly degraded by extracellular RNAses + it is not internalized efficiently. → Thus a great variety of transfection reagents have been developed to facilitate cellular uptake of mRNA + protect it from degradation. Immunogenicity: Since exogenous RNA is considered a non-self molecule, our immune system can recognize it as foreign and induce the innate immune response.

Immunity against helminths

mediated by the activation of TH2 cells, which results in production of IgE antibodies and activation of eosinophils. Steps: 1. Production of IL-13 (by Th2) → strengthens the epithelium of the gut (the layers become more tightly connected) to protect it from infection. → stimulates production of mucus 2. Production of IL-5 (by Th2) → recruits and activates eosinophils → granules release toxic molecules (e.g. Major Basic Proteins - MBP) close to the flatworm → dies → expelled in feces 3. Antibody class switching to IgE → IgE can bind to the parasite → Fcε recognized by receptors of eosinophils + basophils → degranulation close to parasites → promoting flatworm death. 4. Production of IL-3, IL-9, IL-33 → guide the recruitment of other granulocytes (basophils, mastocytes) → degranulation of vasoactive molecules → contraction of intestinal vascular smooth muscle → stimulation of peristalsis to favor parasite movement out from the intestine.

Asthma

most common Type I hypersensitivity Allergenes: Pollen / animal hair / dust mite feces Entry route: inhaled Response/symptoms: Inflammation & edema of lower airways with mucus production / bronchial constriction → more severe than hay fever.

immunodeficiency

ompromised/absent ability of the immune system to fight infectious diseases ~Opposite of hypersensitivities ⇒ Increased susceptibility to infections, cancer, autoimmunity * Primary and secondary

Light chain recombination

only happens in B cell maturation, V and J regions imprecise - Rearranged into Kappa/ Lambda light chains

Function of IgG

opsonisation complement activation toxic neutralisation cell-mediated cytotoxicity neonatal immunity → crosses placental barrier (FcRn)

Clinical use of MoAb

over 30 recombinant MoAbs with trademarks up to now, and hundreds involved in clinical trials. - Omazilumab →Blocks IgE to reduce allerginc response - Blockage of HER2: Causes cancer cells to not receive GFs - Car-T (chimeric antigenic receptor-T): T cells that are genetically engineered to produce an artificial T receptor able to target a specific protein. In this way, they are no longer restricted to MHC and peptides since it is a chimeric molecule.

Eosinophils in allergic reaction

part of the allergic inflammation (can bind to IgE though have less receptors) but not as significant. They're activated by cytokines (e.g. IL-5) and release preformed and Neoformed molecules * May be significant against parasites = release antiparasitic molecules e.g., peroxidase.

Allergen penetration and activation

penetrates paracellularly through gap junctions --> recognised by iDC --> maturation and migration to lymph node --> Presents allergen to naive Th --> Th2 stimulates isotype switching in B cells into IgE --> IgE is secreted into the blood; recognised the allergen, causing an immune reaction. * Mast cells is activated by IgE and secretes it granules = Histamine, Serotonin, Proteases. * Upon a 2nd encounter - early and intermediate phases (lipid mediators); inflammation.

Long-term non-progressors of hiv

positive people whose infection progresses to AIDS slowly 1. Controllers (1% of all infected ind.) They have low viremia Remain healthy for 10-15 y or even don't get infected after exposure to virus. Thanks to a protective genetic trait: Homozygotic deletion of the CCR5 receptor → virus can't infect cells 2. Elite controllers (0.3% of all infected ind.) They produce neutralizing antibodies that can limit the infection

Immunity against Protozoa

principal defence mechanism against protozoa that survive within macrophages is cell-mediated immunity, particularly macrophage activation by TH1 cell-derived cytokines.

Injurious Effects of Immune Responses to Extracellular Bacteria

principal injurious consequences of host responses to extracellular bacteria are inflammation and septic shock 1. Superantigens = resemble MHC2 and overactivate T cells 2. Protein SSLP7 = binds in-between the IgA Abs and the C5 complement protein that binds to the pathogen, so that the macrophage won't recognize the pathogen through the its receptors or through the complement system. * Usage of antibiotics is used against these types of infections

Papain

protease enzyme able to cleave the antibody molecule into functionally distinct fragments by cutting the antibody on the amino-terminal side of the disulfide bonds between two heavy chains

TdT (Terminal Deoxynucleotide Transferase)

randomly inserts(/removes) nucleotides, without the need of a template = N nts. Random → may be dangerous (e.g. a stop codon is introduced) → can lead to apoptosis of the developing lymphocyte.

Hapten

small molecule that has to bind to a larger molecule to form an antigen - Need carrier to elicit response

Other antigens (Except ABO) determining blood groups

some minor antigens (e.g. Ag Lewis) that are involved (modified by other enzymes, e.g. fucosyltransferases) producing new epitopes - but they're of lower importance. Rh is one of them

Why is it hard to control hypersensitivity immune responses?

stimuli for these abnormal immune responses are difficult or impossible to eliminate (e.g., self antigens,commensal microbes, and environmental antigens) and the immune system has many built-in positive feedback loops (amplification mechanisms) = Tendency to become chronic

Complementary determining regions

the acronym for CDR; names given to the hypervariable loops of the heavy chain in receptors in antibodies and lymphocyte receptors - CDR1/CDR2 → in V fragment - CDR3: heavy → D fragment; light → V or J fragment

Stimulatory role of the immune system on Cancer development

the immune system often does the opposite from what it should - by triggering inflammation, esp. chronic inflammation in the tumor's microenvironment. - cytokines (e.g. IL-6) that should theoretically help fight off the cancer - it actually provides a stimulatory factor for the cancer's growth and promotion

Transplant immunology

the process of taking cells, tissues or organs, called grafts from one individual and placing them into another - Transplantation of cells or tissues from one individual to a genetically non-identical individual invariably leads to rejection of the transplant due to an adaptive immune response. = Rejection

Cancer immunotherapy

treatment of cancer by stimulating the patient's own immune response. Current treatment inhibit or kill cancer cell but also harm healthy tissues. Immunotherapy has the potential to be specific.

Acquired ImmunoDeficiency Syndrome (AIDS) & HIV

two species of Lentivirus (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. Without treatment, average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype

Enh enhancer

variable fragments that have a promoter in the 5' end (before every L segment); the transcription machinery must attach to the promoter and the enhancer to transcribe the sequence otherwise the locus cannot be transcribed * a security system, since there is the deletion of the sequences in between which means that recombination has occurred.

ILC, γδ T, αβ T

ɣ𝛿T → play important functions in wound healing, removing distressed or transformed epithelial cells and subduing excessive inflammation. 𝛂βT → mainly mediate cell immunity and immune regulation. ILC - innate lymphoid cells

IgG function

• Most abundant antibody • Enhances phagocytosis by opsonisation • Only antibody to cross the placenta from mother to fetus - Also enhance ADCC - Serves as a bridge between MHC1 of a viral infected cell to a CTC CD16 and cause the release of granzymes and perforin

Genetic deficiencies in MAC components

→ Neisseria spp. infections only

Genetic deficiencies in the MBL pathway

→ bacterial infections | mainly in childhood

B & T cell Interaction

→ complete B cell activation: They proliferate & differentiate into short-living, IgM-producing plasma cells (occurs outside the follicle). A few other B cells re-enter the follicle with several T helper cells that differentiate into follicular helper T cells (Tfh)

Genetic deficiencies in the alternative pathway

→ pyogenic / Neisseria spp. infections

Genetic deficiencies in C3b deposition

→ pyogenic / Neisseria spp. infections | can sometimes lead to immune complex disease

Alteration of antigen processing + MHC presentation

→ the virus may affect any one of the antigen presentation steps: Inhibition of the proteasomal activity (Epstein-Barr Virus / Cytomegalovirus) Inhibition of TAP channels of the ER (Herpes Simplex Virus) Removal of class I from ER (Cytomegalovirus) / blocking MHC synthesis Production of 'decoy' receptors that inhibit the physiological mechanism of AP.

immunosenescence; alterations of B cells

↓ B-T cell interaction (= ↓ aid of Th1 in Ig class switching of B cells) → poor response to new T-dependent antigens = IS is less able to respond to new vaccines & newly introduced pathogens → ↓ production of specific Abs However - ↑ production of non-specific Abs ↑ auto-Abs ↑ monoclonal gammopathies ↑ clonal expansion of lymphocytes → lymphocyte malignancies

immunosenescence; alterations of T cells

↓ naive T cell output This is viewed by looking at TREC (a marker of naive T cells produced in the thymus (it results from somatic recombination). Indeed it decreases in age On the other hand - there's an ↑ in memory cells (central + effector memory) - Bone marrow producing mostly 'occupied' and not naive T cells.

Key features of immune senescence

↓ number of T cells overall, but ↑ proportion of memory cells (in respect to naive cells that ↓) Memory cells are specific for latent viruses (e.g. CMV, HSV) Most of them have T​EMRA​ phenotype =​ ​CD28-, CD54RA+ Possible altered CD4:CD8 ratio (CD4 ↓ CD8 ↑). ↑ amount of, usually nonspecific, Abs ↓ number of B cells (imapired interaction w/ T cells) ↓ responsiveness towards new antigens & vaccines Inflammaging

Hallmarks of ageing in the cellular level

● Genomic instability, ● Telomere attrition, ● Epigenetic alterations, ● Loss of proteostasis, ● Deregulated nutrient sensing, ● Mitochondrial dysfunctions, ● Stem cell exhaustion, ● Altered intercellular communication, ● Cellular senescence