Immunology

Describe the structure + properties of IgM

"macroglobulin": pentamer MW 900,000 Bound to J chain First produced in the immune response - class switching to more specialised antibodies occurs later (eg: IgG) Mainly found in blood due to large size No hinge regions - doesn't need extra flexibility Relatively low affinity - so many opportunities to bind it doesn't need to bind strongly Can have high avidity

What is the difference between MHC 1 and 2?

1 - expressed by nearly all cell types (nucleated - not RBCs) - single transmembrane tail, peptide binding cleft, alpha 1 and 2 domains 2 - expressed by antigen presenting cells, 2 transmembrane tails, peptide binding cleft from beta 1 and alpha 1 domains

What MHC do antigen presenting cells express?

1 and 2 in nucleated cells

What are the purposes of antibodies?

1. Bind specifically to epitopes on the pathogen/antigen that elicit the immune response - neutralisation/opsonization 2. Recruit cells and molecules to destroy pathogen/antigen - region in effector function is the constant - FC

What are the functional categories of cytokines?

1. Mediators and regulators of innate immunity - produced mainly by macrophages in response to infectious agent 2. Mediators and regulators of adaptive immunity - produced mainly by T lymphocytes in response to specific recognition of foreign antigens 3. Stimulators of haematopoiesis - produced by bone marrow stromal cells, leukocytes and other cells and stimulate the growth and differentiation of immature leukocytes

What is the normal proportion of lymphocytes in the blood? When are they elevated?

16-46% in adult blood smear, increased in infectious mononucleosis, lymphocytic leukaemia + more

Describe the C1r, C1q and C1s complex

2 x C1r, 1 x C1q, 2 x C1s FC binding globules - for antibody stem binding C1q antibody can bind to - aligning pathogen with C1 with antibody conjugate

Describe the 4 chain structure of IgG

2 x inner heavy chain, hinged + joined by a disulphide bridge, each made of a variable region, constant 1, constant 2 and constant 3 - 50kDa each Heavy determines antibody isotype, glycosylation on heavy 2 + 3 - modulates binding to FC receptors on cells 2 x outer light chain, 2 domain structure of variable and constant - 25kDa each Variable regions = binding sites, N terminus (start of protein sequence) Constant regions = C terminus (end of protein sequence)

How is polymorphism of MHC ensured?

3 genes encode alpha chain 3 from mother + 3 from father - increases variation - 6 possible variants for MHC1 and 12 for MHC2 (alpha + beta chain)

Describe the hypervariable sections of antibodies

3 in light chain, 3 in heavy chain = 6 areas for variability on each side - 12 in total

How are peptides bound by MHC?

A single MHC molecule binds a single peptide at a time, but can potentially bind different peptides Broad specificity ensures that an individual can present many different peptides to T cells Polymorphic residues of MHC are in peptide-binding domains and affect specificity Differences in MHC molecules affect immune responses

What killing mechanisms exist for phagocytosis?

Acidification - pH 3.5-4 bacteriostatic or bacteriocidal Toxic oxygen products - Superoxide O2-, hydrogen peroxide (H2O2), singlet oxygen 1O2., hydroxyl radical OH., hypohalite OCl- Toxic nitrogen oxides - Nitric oxide (NO) Antimicrobial peptides - Defensins, cationic proteins Enzymes - Lysozyme, acid hydrolases Competitors - Lactoferrin (binds iron), vitamin B12 binding protein

What are the additional functions of macrophages (besides phagocytosis)?

Activated by bacterial products or cytokines Secrete cytokines - soluble factors Present antigens to lymphocytes

What are the characteristics of NK cells?

Activated by cytokines + produce cytokines Upregulated early on Activated by: IFNα,IFNβ (Type I) and IL12 (interferon and interleukin= cytokines) NK cells can produce IFNg (helps control infections) Contain viral infections whilst adaptive/specific response kicks in Deficiency -> increased risk of herpes(rare)

How does immunotherapy work for cancers?

Activating the immune system to fight cancer Antibodies used to bind to tumours or cytokines Tumour peptide injections to stimulate CD8 cells Drugs that release the immune system blocks that cancer cells can produce Fighting cancer - vaccines or monoclonal antibodies - deliver drug targets to specific sites Tumour cells convince body they're self - therapy to prevent this negative regulation created

Which cells are responsible for extracellular killing?

Active against organisms too large for phagocytosis (helminths), infected cells Eosinophils - bridging innate + adaptive Natural killer cells - innate cells but lymphoid in origin (lack antigen specific receptors), active against viral infected cells, attacks some tumour cells, not sophisticated, granzyme, perforin

What is the difference between affinity + avidity?

Affinity = strength of binding between a single antibody binding site + an epitope Avidity = strength of binding between antibody + antigen, affinity of and number of antigen binding sites - greater than single site affinity

Describe the functions of IgM

Agglutination Complement activation B cell antigen receptor in monomer form Produced rapidly - important for 1y response Protects from common pathogens in mucosal areas

What are the cells of the immune system?

All from bone marrow Lymphoids split into all different lymphocytes: B cells - mature in bone marrow T-cells - mature in thymus NK cells - no specific antigen recognition (unlike B/T) Immature dendritic cells - in tissues Mast cells, macrophages - in tissues Monocytes in blood differentiate into macrophages in tissue

Describe the T cell receptor

Alpha and beta chains linked by disulphide bonds Structurally similar to the antibody chain (variable region) Has variable region - bind to lots of different antigens Always bound Constant and variable regions - Ig domains Constant region does not activate other immune cells Both chains have hydrophobic trans-membrane region and short intracellular tail

Describe the classical complement pathway activation

Antibody binds to specific pathogen IgM = pentameric antibody binds, globular heads on C1q, FC portion of antibody can bind to C1q Only one pentamer needed IgG = individual antibodies also bind Cascade begins - one pentamer of IgM or 2 molecules of IgG required

What is ADCC?

Antibody-dependent cell-mediated cytotoxicity Recruiting cells to release different proteins/enzymes that may damage target cells

Define antigen and epitope

Antigen - molecule that induces an immune response Epitope (antigenic determinant) - sub-region of an antigen which is recognised by a specific immune antigen receptor, multiple epitopes on one antigen

What are chemokines?

Attracting inflammatory cytokines to infection site 2 groups - CXC, CC More than 50 exist

What is rheumatoid arthritis?

Autoimmune disease associated with IL-17 synthesis Inflammation and production of autoantibodies Develops with age Complex genetic condition - many aetiologies

What are the B lymphocyte receptors?

B cell receptor (BCR) BCR = anchored form of an antibody Surface anchored Ig binds free antigen

What future therapies are being explored for UTIs?

Barrier creams that prevent gut bacteria from colonising and infecting urogenital tract Methenamine Hippurate metabolised to formaldehyde produced in urine to kill bacteria - excreted in urine

How do antibodies neutralise?

Binding - FC portion binds to receptors of specific cells to engulf that virus Preventing interaction with cell receptors Prevents uptake of pathogen by target cells Can include toxins Uptake and destruction by macrophages

How do antibodies opsonise?

Binding to mark for phagocytosis Direct = Binds and coats pathogen, FC binds receptor to cause engulfment Indirect = increase complement C3b to coat pathogen, antibodies and C3b coating, binds to CR1 (complement receptor) Complete protein required

How do antibodies agglutinate?

Binds round the surface of a threat - forms a clump Easier for immune system to detect Agglutination tests - what bacteria is present in samples, +ve indicator = bacteria binding together

What infections occur as a consequence of UTIs?

Bladder infection - cystitis Kidney infection - pyelonephritis Track up further without antibiotics (septicaemia if in bloodstream)

What are the primary organs of the immune system?

Bone marrow (in foetuses - liver) - soft, spongy, highly cellular tissue that fills the internal cavity of bones - B cells, T cell precursors (virgin lymphocytes) Clonally diverse - each cell has a single specificity of receptor, cells are specific to antigen Thymus - 2 lobes, above the heart and behind the sternum, mature T cells

Describe differentiation of B + T cells

Both B and T undergo 2 stages of differentiation 1. Differentiate from pluripotent stem cells in bone marrow 2. Undergo further differentiation in response to antigen Interleukin 2 - stimulates T cells Therefore a specific immune response is an adaptive response -> specific/adaptive immune response -then proliferate (IL-2 stimulates T cells) - lots of active cells Lymphoid derivative

What is the purpose of inflammation?

Brings cells + molecules from blood into a site of infection Increased blood supply - vasodilation Increased vascular permeability - leaky Increased expression of adhesion molecules

Describe the classical complement pathway

C1q has 6 globular heads joined to common stem, at least 2 globular head of C1q must bind to Fc domains for activation of C1q Binding of C1q leads to conformational change which reveals proteolytic site on C1r C1r has enzymatic activity - cleaves C1s to generate serine protease C1s (one C1r on each side cleaves each C1s) C1s cleaves C4 and C2 (protease - breakdown C4) C4 broken down to C4a and C4b (larger) C4b binds covalently to the pathogen surface (antibody and C1 already attached) C2 binds to C4b on antigen or pathogen surface C2 is cleaved by C1s leaving the C4b2a complex (C2a = larger) (C2 - C2a and C2b) C4b2a = C3 convertase - most important component C3 convertase cleaves large numbers of C3 molecules to C3b and C3a C3b joins C4b2a3b = C5 convertase Main effect = lots of C3b on surface of pathogen (opsonin for more phagocytosis) and makes C5 convertase Bound C3b can activate alternative pathway - further amplification effects C3b = reactive thioester bond which is exposed after cleavage, allows C3b to bind covalently to the pathogen surface If it does not bind to the surface of a pathogen almost immediately it is rapidly hydrolysed by water and becomes inactive (control)

How does the complement system cause inflammation?

C3a/C5a = proinflammatory, anaphylatoxin Increase permeability, leaky, proteins/cells/liquid escaping Vasodilation Chemotactically attracted to site - antibodies

Describe the MAC phase of the complement system

C5 binds C43a3b complex (C5 convertase) C5 - C5a and C5b = potent inflammatory C5b binds to pathogen surface and binds C6 C5b6 binds C7 = C5bC6C7 Conformational change and C7 inserts into the lipid bilayer of the pathogen wall Forms polymer - hole in pathogen surface for lysis and death C5b67 then binds C8 C8= C8b +C8α-g C8b binds to C5b (allows binding of C8α-g) C8α-g inserts into the lipid bilayer C8α-g induces polymerization of 10-16 molecules of C9 ->forms a ring structure C5b6789 = MAC

How does the T-cell receptor signal?

CD3 complex - only found on T cells, secondary activation, safeguarding process Binding of MHC activates signalling cascade, CD3 also has this to lead to cytokine production ITAMS - involved in signalling cascade, immune receptor tyrosine-based activation motif

What is the role of T helper cells?

CD4+, recognise antigens taken up by antigen presenting cells Presented on surface by MHCII Modulates activities of cytokines Depletion of these = infection + tumours

How do cytotoxic T cells kill infected cells?

CD8+ - transmembrane glycoproteins Recognise viral antigens presented by MHCII on infected cells Perforin and granzymes - no infected cell will escape Causes apoptosis

What is type 2 hypersensitivity?

CYTOTOXIC Type Hypersensitivity IgG and IgM involved in reaction eg: Erythroblastosis fetalis - mother resus negative, pregnant with 1st resus positive child, mother produces cells against factor, 2nd pregnancy - another resus positive baby, antibodies cross placenta and attach resus positive of baby - baby can severely lack RBCs

What are MHC?

Cell surface glycoproteins Part of Ig superfamily CD8+ recognise MHCI, CD4+ recognise MHCII Encoded by HLA genes in HLA complex/cluster I = HLA-A, HLA-B, HLA-C II = HLA-DP, HLA-DQ, HLA-DR Highly polymorphic - lots of different varieties in one population

What is the HLA-locus? What are the properties of the HLA-locus?

Chromosome 6 Polygenic - several loci encoding proteins of identical function, differ genetically Polymorphism - no 2 individuals with the same MHC apart from identical twins Vital to survival

What are the problems with phagocytosis?

Chronic granulomatous disease (CGD) - recurrent infections (bacterial/fungal) Leukocyte adhesion disease syndromes (LAD) - unable to make pus

How is the complement system activated?

Classical - antibody required, bind to pathogen, antigen-antibody complexes Lectin - mannose-binding protein (acute-phase, made in liver) binds pathogen surface (glycoproteins/CHO) Alternative pathway - pathogen surface creates local environment conductive to complement activation, causes some breakdown

What are the complement system proteins?

Classical = C1(q, r, s), C4, C2 Alternative = Factor D, factor B, properdin (factor P) Both pathways use C3 + membrane activation complex (MAC) - C5, C6, C7, C8, C9

How do antibodies activate complement?

Classical pathway - binding of antibodies (1x IgM/2x IgG) Antigen-antibody complex binds C1qrs to start complement system to produce C3 convertase downstream (by acting on C4 and C2)

Describe the nomenclature of the complement system

Classical pathway = C1-9, cleaved by enzymes to a and b forms Alternative pathway = B/D Normally large fragment = b, small = a (except C2)

What are UTIs?

Commonly affect women - faecal materials reach the urethra Recurrent + painful infections Treated by antibiotics - cause of resistance Caused by E.Coli that resides in gut - uses pili to attach to cells + flagella for motility, UPEC

Describe the variable and constant light domain structures of an antibody

Compact Ig domains - 100-110 AAs 2 sheets of beta strands Intrachain disulfide bond Used elsewhere of antibodies Hypervariable sections within variable sections - where AA sequences vary lots

What are domains?

Compactly folded globular units within protein Small proteins may be single domain, large proteins often consist of multiple domains Domains may form functional units within proteins (e.g. V domains of Ig --> Ag binding) Evolutionary significance

How do TH17 impact infection?

Control infection by extracellular bacteria and fungi Interleukin 17 cytokine Recruits and promotes response by neutrophils - protect and control infection Promotes production of antimicrobial peptides in epithelial cells

How do TH2 impact infection?

Control infection by extracellular parasites - helminths Produce cytokines - Interleukin 4 cytokine Recruit and promote eosinophils and mast cells Required for B cell class switching to IgE - fight parasites Type 2 response - high antibody titre (lots of IgE)

Which antibiotic is currently recommended for UTIs?

Current recommendation is nitrofurantoin - bacteria find it difficult to develop resistance

What are the consequences of deficiencies in C6, C7, C8 or C9?

Cytolysis impacted Problems with infections of Neisseria - susceptible to gonorrhoea and meningitis (no MAC)

Describe the alternative complement pathway

Different C3 convertase, C3 undergoes spontaneous hydrolysis C3b binds surface, factor B binds C3b (C3b may have come from classical pathway) Cleaved by D = C3bBb (C3 convertase does the same as other convertase, made of different subunits) C3bBb is the same as C4b2a Bb is formed when B is split into Ba and Bb Factor P = properdin, stabilises C3 convertase C3bBb add another C3b - C3b2Bb = C5 convertase C5 = C5a and C5b C5bC6C7C8C9 = MAC Can be activated by actions of other 2 pathways - not independent

What is secondary immunodeficiency?

Different condition = effected Causes: malnutrition (severe anaemia, bulimia), immunosuppressive/cytotoxic drugs, infection - measles, HIV, stress, lymphoproliferative disease

Describe clonal selection of lymphocytes

Each lymphocyte has different specificity - different targets Remove lymphocytes that will attack self - killed via apoptosis (self-antigen binding) Left with pool of naïve lymphocytes - not encountered foreign antigens Come into contact with foreign antigen Lymphocyte becomes mature, multiplies to produce effector cells

Describe antigen driven lymphocyte clonal selection

Each receptor specific to each epitope When exposed to antigen that matches epitope, cell-line 2 proliferates Peripheral lymphoid tissue Create more of matched cell - antigen specific Memory cells/plasma cells Plasma cells - ER to make more antibodies for the antigen specific to the epitope Proliferation is dependent on exposure to the antigen

How are antibodies produced?

Each resting B cells (surface Ig) - one antigen specificity Contact with antigen activates B cell - divides Differentiates to plasma cells secreting antibody with same specificity as Ig

What happens during local inflammation?

Eg: gram -ve bacteria from a cut onto the hand PRR on macrophage stimulated Release of TNF alpha but controlled Positive outcome

What is the difference between exogenous and endogenous antigens?

Endogenous - made in cytoplasm, self + viral, presented by MHC1 Exogenous - proteins made outside of cell/in vesicles = foreign, parts of bacteria, virus or vesicles, presented by MHC2 Must be processed to peptides before binding MHC

How do antigens get presented on cell surface?

Engulf antigen - forms endosome of neutral pH Influx of H+ ions, acidic endosome = activated Degrades peptides into small compounds which are bound to MHC 2 Moves to surface and presented on cell surface

How do NOD2 receptors work in a healthy individual?

Epithelial cells contain lots of NOD2 receptors Secretory granules containing antimicrobial peptides Epithelium normally safe from bacteria Normally have plenty muramyl dipeptide Bacteria grown in food broth, bacteria divide - overgrowth in broth Threaten epithelium - increased risk of infection Lots of muramyl dipeptide, endocytosed to epithelium Recognised by NOD2 - signalling cascade Release of AM from cells into gut lumen AM kill bacteria - form pores and lyses them AM attract macrophages from lamina propria/blood to mop up any remaining bacteria Gut returned to homeostasis + body protected by infection

How do TH1 impact infection?

Eradicate intracellular pathogens that can survive or replicate in macrophages Pathogens are phagocytosed by macrophages but evade killing - survive in lysosome TH1 enhance killing power - type 1 response Interferon gamma used to enhance mycobacterium killing

What is endotoxic shock?

Excessive cytokine release in gram negative bacterial infection Widespread effects of cytokines on vascular endothelium Circulatory shock - low blood pressure, organs don't get blood needed Disseminated intravascular coagulation (DIC) - blockage of vessels etc

How can pathogens cause tissue damage?

Exotoxin production - bacteria producing toxins Endotoxins Direct cytopathic effect - damage to cells Pathogen damage - infectious agent damaging host directly

Describe the healthy mechanisms acting against UTIs

Extracellular TLR5 receptor - recognise flagella for ascending infection, UPEC binds TLR5 Signalling response and release of AMP to clear the infection E.coli from GI tract contaminate uro-genital tract (uropathogenic E.coli) Detected by uro-epithelial or bladder cells via TLR5 which is extracellular and recognises flagella proteins (flagellin) Activated TLR5 stimulates defensin release (innate response) Defensins disrupt bacterial membrane and kill E.coli Bacteria cleared & uro-epithelium protected

How are exogenous antigens presented with MHC2?

Extracellular antigen phagocytosed by antigen presenting cells Phagosome and lysosome fuse to degrade to small chunks MHC II in ER, invariant chain bound Prevents binding to peptide groove - ensures MHC does not auto respond Moves through Golgi vesicles where invariant chain released as protein is ready Antigen is engulfed by APC (e.g. dendritic cell) (phagocytic pathway) Protein cleaved to peptide fragments by acid activated proteases Vesicles with peptides fuse with vesicles containing MHC II molecules MHC class II molecules binds peptide fragment + transported to cell surface Takes 1-3h

What are the 2 fragment sections of an antibody?

FAB = fragment antigen binding - top of Y shape FC = fragment crystallisable - constant heavy 2 + 3

How can immunoglobulins be cleaved enzymatically?

FAB = smaller than globular proteins, delivers drugs to specific sites Proteolytic cleavage by papain

Why do drugs only use FAB not FC action on antibodies? Give an example

FC causes a potent immune response - can be auto Mast cells - allergic responses (IgE binds and activates) IgE - antigen that binds to several at once to activate this mast cell - avoids histamine response all the time IgE crosslinked - binding together to activate mast cells - 2-3 antibodies Histamine = v potent

What are the primary lymphoid tissues?

Foetal liver, bone marrow B-cells - mature B cells T-cell precursors - thymus - mature T cells Mature lymphocytes are clonally diverse with respect to the specificity of their antigen receptors: i.e. each cell has a single specificity of receptor

Describe the innate immune system

From birth Targets any antigens Simple recognition systems - not advanced, acts quickly Limited capacity Present before infection starts/patrols for infection Recognises common danger signals Rapid response - within minutes No memory - no antibody response etc

What are the heavy chain isotypes of antibodies?

Gamma, mu, delta, alpha, epsilon Differ in size, structure + function of the constant region Determine antibody class = IgM, A, D, G, E

What factors effect immunity?

General health Infection Nutrition Adverse environmental conditions State of microbiome - linking factor Pregnancy - reducing immune system so foetus not seen as foreign/pathogenic - more susceptible Genetic disorders Stress

How do CD8 and CD4 stabilise MHC recognition?

Glycoprotein co-receptors Help T cells come into close proximity with MHC Keeps contact for long enough for process to take place - cascade and cytokine transcription

Describe MHC 1

Heterodimer found in nucleated cells 3 alpha units with 1 beta 2 microglobulin - smaller than class 2 One transmembrane domain (alpha-3) Binds small peptides - 8-10AA Alpha chain = 44kMW, beta = 12kMW Alpha 1 + 2 = peptide binding region, polymorphic AA found here, line the bottom + side of groove Alpha 3 + beta 2 = Ig-like Peptide binds by H and ionic bonds Variability in peptides needed to form cleft

Describe MHC 2

Heterodimer with alpha and beta domains of the similar size - both transmembrane Both chains are polymorphic + encoded by MHC Alpha 1 and beta 1 domains = peptide binding site Alpha chain = 34kDa, beta chain = 29kDa Binds longer peptides - 13-24 AA Binds exogenous peptides - from outside of cell Alpha 2 + beta 2 = Ig-like

How is oxygen dependent killing carried out?

Hexose monophosphate shunt generates NADPH NADPH oxidase generates reactive oxygen intermediates Reactive oxygen intermediates = bacteriostatic, bacteriocidal H2O2 + myeloperoxidase + halide ---> halogenation and killing

What are the types and properties of MALTs?

High surface area GALT, BALT (bronchus) Adenoid, tonsils - BALT Peyer's Patch - GALT More diffuse, localisation of cells Non-encapsulated submucosal lymphoid nodules and diffuse lymphocytic infiltrates in the submucosa of intestinal and respiratory tracts

What is the difference between humoral and cellular immunity?

Humoral - covers extracellular fluid, transferred with serum, directed against "free antigen", make contact with antibodies - B cells Cellular - specifically cell responses, transferred by cells, directed against cell-associated antigens (intracellular pathogens) - T cells Do not fit into adaptive/innate

Describe antibody antigen binding sites

Hypervariable Complementarity-determining regions (CDR) - 6 on each side 3 loops of HV on each H and L chain The six CDR form the antigen binding sites Framework (other loops and strands) less variable

What cytokines do T regulatory cells secrete?

IL-10 Anti-inflammatory Suppress immune activation

What cytokines do TH17 cells secrete?

IL-17, proinflammatory anti-microbial immunity at epithelial/mucosal barriers recruit neutrophils

Which cytokines are produced by macrophages? What is their main role?

IL-1beta, TNF-alpha, IL-6, CXCL8, IL-12 Raising body temperature to slow down pathogenic growth - fever, working in hypothalamus Inflammation - return of homeostasis, chemotactic, acts on vascular epithelium Acute phase response - acts on liver Acts on lymphocytes - affect type/properties - influence the function

What cytokines do T-follicle helper cells secrete?

IL-21 Helps B cells become antibody secreting cells

What cytokines do TH2 secrete?

IL-4 - proinflammatory Class switching to IgE Recruits mast cells, eosinophils + basophils Produces more TH2

Describe the distribution of Ig in the body

IgG and IgM predominate in the blood IgG and monomeric IgA predominate in extracellular fluid Brain is devoid of IgG Dimeric IgA predominates in secretions (mucosal membrane) + breast milk The foetus receives IgG from the mother IgE is associated with mast cells just below epithelial surfaces

What are the antibody isotypes?

IgM, A, D, G, E - produced at different times and locations IgM exists when first meeting antigens, more glycosylated - pentamer form IgG exists on its own IgA has a dimer form - 2 together IgG and IgD have different hinge forms - impacts flexibility + binding

Describe the action of the immune system during an infection

Immediately innate - engulfs pathogens Dendritic cells (antigen presenting) take up pathogen and move to lymph nodes by lymphatic system - present antigen to T cells to activate adaptive T cell proliferation + differentiation - helper, cytotoxic Move to site of infection to clear pathogen

How can the immune system cause tissue damage?

Immune complexes - agglutination, large complexes getting trapped and causing localised immune responses that aren't necessary (kidney disease and damage) Anti-host antibody - antibodies binding directly to own cells thinking they are pathogen, rheumatic fever, normally B cells removed Cell-mediated immune damage - producing cytokines that cause damage to own cells

What is immunopathology?

Immune responses cause problems for host - excessive, ineffective, inappropriate Infection, allergy, autoimmune disease Different immune mechanisms

How does herd immunity work?

Immunisation can protect the individual + the population Disease declines if majority of the population are immune

What are the characteristics of neutrophils?

Increase greatly during infection, most common WBC in circulation Respond quickly Drop low - vulnerable to infection, eg: chemotherapy, sepsis in times of neutropenia short-lived cells (<24hr) multi-lobed nucleus (polymorphonuclear (PMN) cell) abundant in sites of acute inflammation

Give examples of tissue damage

Infectious agent Immunodeficiency Vaccination Immunopathology Hypersensitivity - Allergy + autoimmunity Tumour immunology

Describe the mechanism behind rheumatoid arthritis

Initial dysbiosis in gut, selects for segmented filamentous bacteria (E.Coli in humans?) (cause not known) Over-attach to epithelial cells - signalling cascade Consequence - differentiation and proliferation of T helper (17) cells - bloodstream + circulation from lamina propria IL-17 synthesis (pro-inflammatory cytokine) Activation of autoreactive B cells (innate-adaptive response) - production of autoantibodies - protein deposition in joints - autoimmune Arthritis

Describe the course of the immune response

Initial recognition - 2 weeks for antibody response Secondary response - more rapid, higher levels of antibody concentration IgM (quick response) - IgG (tailored/specific) More IgG with secondary response Vaccines - higher levels of IgG and memory T cells as well

How do cytokines work?

Initiate their actions by binding to specific membrane receptors on target cells External signals regulate the expression of cytokine receptors and the responsiveness of cells to cytokines The cellular response to most cytokines consists of changes in gene expression in target cells, resulting in the expression of new functions and sometimes proliferation of the target cell

What cytokines do TH1 secrete?

Interferon gamma activate macrophages (help kill ingested pathogens) + NK cells produce more TH1

How do genetics impact susceptibility to IBD?

Intracellular pathogen-recognition receptor NOD2 - involved in innate response - binds muramyl dipeptide (peptidoglycan component of gram +ve and -ve bacteria) Autophagy genes ATG16L1 + IRGM Transcription factor XBP1 (stress response impacting protein folding)

What is primary immunodeficiency?

Intrinsic defect - genetics, born with it Rare, dominant or recessive, autosomal or X-linked May or may not be identified eg: SCIDs

How may the gut microbiota influence rheumatoid arthritis?

Involves response at sites distal to the gut found in mice studies Genetically engineered mouse to produce autoantibodies produce glucose 6 isomerase Maintained in germ-free and gut commensal environments Germ-free = no arthritis Commensal flora = rheumatoid arthritis, autoimmune Something in the microbiota predisposing mice to arthritis Most severe cases - received segmented filamentous bacteria - part of gut microbiota, filamentous gram +ve

What are the light chain antibody isotypes?

Kappa/lamda Gives no functional difference Cannot be both

What are the functions of T cells?

Kill virus infected cells Modulates activities of other B cells and helper T cells

What is the primary bacteria of the urobiome?

Lactobacillus - produces lactic acid, few other bacteria can grow, gatekeeper to urinary tract

Describe the appearance of a normal small lymphocyte

Large nucleus - same size as an RBC Pale blue cytoplasm + dark stained nucleus

Describe the appearance of a larger lymphocyte + how they are formed

Larger More granular cytoplasm A small lymphocyte, B-cell or T-cell, becomes a large lymphocyte as it is stimulated to proliferate Such a cell can be shown to be able to incorporate tritiated thymidine, a marker of active DNA synthesis

Describe the antibody response to an antigen

Latent period to allow immune system to start working IgM first, then IgG

How are antibodies used in the lab? Give examples of techniques

Lateral flow tests Flow cytometry ELISA test Immunoprecipitation Fluorescence microscopy Western blot Antibody binding specifically to target à visual response

Describe the spleen

Left side of abdomen High % of lymphocytes in white pulp area - similar functions to the lymph nodes Like lymph node Good blood supply in red pulp Macrophages for phagocytosis Removes RBCs that are not needed - phagocytoses old RBC

What are the properties of cytokines?

Link innate and adaptive Low molecular weight proteins (5-25kDa) secreted by cells that stimulate or inhibit the activity, proliferation or differentiations of other cells Small but potent 20 - not clear nomenclature Subgroups - interferons, chemokines, lymphokines, interleukins Stimulate/activate cells Secretion is a brief, self-limited event The action is often pleiotropic (multiple biological actions) and redundant (shared biological actions) Often influence the synthesis and actions of other cytokines Action may be local and systemic

What are the different types of vaccine?

Live - typically attenuated to remove virulence Killed - inactivated/dead/attenuated Subunit - protein fragments from virus, synthetic or amplified from virus Gene delivery - mRNA, covid vaccines Type of vaccine depends on particular pathogen and desired response

How does lepromatous leprosy affect the body?

Lots of growth, not walled off - highly infectious Spreads throughout macrophages, more recruited and more transmission Huge antibody production - immune system thinks it will help Bacteria hidden in macrophages - antibodies cannot access them Low T cell response, often die Cytokines - type 1 deficient, greater type 2 response - activating antibody Classic physical symptoms

Describe IgD

Low concentrations in serum d2L2: MW 185,000; d chain: 4 domains, long hinge Can be present on B cells - membrane bound but with IgM Only 2 Ig that get co-expressed Upper respiratory tract to get rid of infections Stimulate basophils and mast cells to release antimicrobial peptides Antigen receptor on B lymphocytes

Describe IgE

Lowest concentrations in serum, very potent effects Binds with high affinity to FcR on mast cells and basophils - release vasoactive/inflammatory mediators Roles in allergy and asthma Important in ADCC and protection against helminth and protozoa infections Induces eosinophils and basophils to release histamine and proteases Several IgE crosslinked for action

What are the secondary lymphoid organs?

Lymph nodes, spleen, mucosal associated lymphoid tissue (MALTs), blood, lymphatics Recirculation of lymphocytes, if they meet antigen they undergo clonal expansion and differentiation Immune responses occur in the secondary lymphoid organs

Describe the structure of lymph nodes

Lymphatic system covers entire body Leukocytes constantly patrolling Primary follicle areas - B cells sit + wait for infection Brings any potential threat through Primary follicles activated - build germinal centres - B-cells proliferate + differentiate Good blood supply for antigen exposure

What are the different types of leukocyte?

Lymphocytes - B, T, NK Monocytes (macrophages in tissue - phagocytic, last longer than neutrophils) Granulocytes Eosinophils Basophils Neutrophils - polymorphic nucleus Mast cells - allergy + anaphylaxis

What antigens do T cells recognise?

MHC 1 and 2 - recognise peptide fragment of antigen on surfaces of other cells in a complex within an MHC

What antigens can antibodies bind?

Macromolecules - protein, CHO, nucleic acids Surfaces of intact protein molecules + other components on pathogen surfaces To epitopes (linear/conformational) Multivalent antigens can bind identical or different antibodies

What are the consequences of inflammation?

Macrophage derived cytokines Complement Mast cells - histamine release T-cell derived cytokines ALL triggered

What molecules are pathogen-associated molecular patterns?

Mannose rich oligosaccharides Peptidoglycans Lipopolysaccharides Unmethylated CpG DNA

How do antibodies cause degranulation?

Mast cells + IgE binding Killing by NK cells and eosinophils (ADCC) Eosinophils = important against parasites

What is humoral specific immunity?

Mediated by antibodies (immunoglobulins) - initially expressed as BCR, then secreted by B cells Surface immunoglobulins (receptors) - make antibodies specific to these only Glycoproteins Present in tissues fluids, serum, binds to epitopes on antigens Can act alone - prevent bacterial adherence, neutralise viruses (prevent viral entry) and toxins (tetanus) Can act as "adaptors" - recognise antigens and interact with innate defence systems (complement (IgG, IgM in classical pathway), phagocytes, eosinophils) Indicator of the specific immune response

Describe IgA

Monomer in serum, dimer in secretions, bound to J chain and secretory component a chain: 4 domains Predominant class in secretions - mucosa 2 subclasses - differ in susceptibility to bacteria proteases IgA1 - serum IgA2 - found in secretions

What are the characteristics of mononuclear phagocytes?

More sophisticated than neutrophils Array of receptors on macrophage blood monocytes, Kuppfer cells, alveolar macrophages etc. Monocytes when in blood, macrophage when in tissue Longer lived cells (months)

Describe the structure + properties of IgG

More specialised Most prevalent in serum - not confined to intravascular compartment Production increased in secondary responses 4 subclasses - differ in structure, functions, abundance, antigens to which they're produced - IgG1-4 IgG1 = most common - 66%, differing hinge structures Hinge for flexibility

What are the functions of IgA?

Most abundant around mucosal membrane Neutralise toxins and pathogens Prevent commensal bacteria from entering bloodstream Inhibition of microbial adherence to mucosal cells Present in early milk--> intestinal protection of neonate

How do NOD2 receptors work in Crohn's patients?

Mutations to NOD2 - not a functional receptor Over-growth of bacteria Muramyl dipeptide binds to receptor but in most cases the signalling mechanism does not work No AMP (defensin) released Innate response does not happen Bacteria breakdown epithelium - microbial populations proliferate ie 'overgrow' and damage epithelium (invasion) Dysbiosis (microbial imbalance) and pathological inflammation Macrophages trying to control, lots of cytokines Imbalance keeps adding to inflammation Greatly disrupted epithelium Pain and diarrhoea - treated by immunosuppressants and steroids

What are the different types of T-helper cells?

Naive from thymus = TH0 Recognise MHCII and become polarised TH1 = activates macrophages TH2 = extracellular parasites, helps B cells produce more IgE TH17 = killing extracellular bacteria/fungi TFH = T-follicle helper cells, stimulate B cells to differentiate + produce antibodies T regulatory = suppresses activation of immune system Each subset secretes different cytokines

How is immunity gained passively?

Natural by placental transfer of maternal IgG Artificial transfer of IgG under special requirements, to very ill individuals/babies with weak immune systems

How is immunity gained actively?

Natural infection or artificial immunisation (vaccination)

Do antibodies phagocytose?

No but they cause it End of complement activation, neutralisation of FC binding Endpoint of several antibody mediated functions Mainly macrophages but can be neutrophils, eosinophils, basophils

What forces allow antibody binding?

Non-covalent forces - van der Waals, hydrophobic interactions, H bonds + electrostatic forces Close interaction - weak bonds

Describe the adaptive immune system

Not present from birth Learns from invading organisms Sophisticated, highly specific recognition à specific strains Slower response (days) - speed increases with exposure Activated in immune organs

What happens after IgA is secreted?

Once secreted - hang around mucosa Neutralising toxins and pathogens Prevents entry to epithelium Once in epithelium - risk of accessing blood + getting different infections

What is the role of the complement system?

Opsonisation - making things more likely to be phagocytosed, some components good at this - C3B Inflammatory response - smaller proteins, vasodilation, C3A and C5A Activating B cells Terminal components of all cascades generates membrane attack complex - lysis of pathogen

What is the consequence of a deficiency in C3?

Opsonisation, cytolysis + inflammation impacted Life-threatening infections from a host of bacteria

How do antimicrobial peptides impact the response to IBD?

Paneth cells produce alpha defensins, goblet cells produce beta defensins Natural antibiotics, hydrophobic Insert into bacterial membranes Create holes in the membrane causing bacteria to lyse Fast response

What are the innate cellular defences?

Phagocytosis (neutrophils/macrophages) Extracellular killing Inflammation - aim, restoration etc

What parts of the blood are part of the innate defence system?

Plasma - clotting factors White blood cells - leukocytes Platelets - clotting

Describe antibody class switching

Post-antigen stimulation - IgM switched to other isotypes Irreversible DNA recombination - cutting + joining of heavy chains Driven by enzymes, cytokine and antigen Eg: pathogen near mucosal site = switching to IgA All different gene segments but all within the same region - same area in order to switch Switching constant portion of heavy chain only Mutation of antigen binding sites - find antibodies that bind stronger - NOT class switching

Describe the functions of IgG

Predominant isotype in serum Large increase in secondary response Complement activation Opsonisation ADCC - antibody dependent cell cytotoxicity Only Ig to cross placenta - IgM = too big, IgG = specialised to broad pathogens, most prevalent

How do T-regulatory cells impact infection?

Prevent T cells responding Inhibit antigen presenting cells Suppress immune response Prevent autoimmunity - IBD, Crohns Switch off T helper cells

What is antibody valency?

Quantity of antibody binding sites IgG = 2 IgM = theoretically 10 - pentamer

What is cell mediated specific immunity?

Recognise epitopes from antigens T cell epitopes are fragments of antigens presented to them by MHC molecules expressed on cell surfaces - processed peptides only!! Captured pathogens MHC - major histocompatibility complex Kills virus-infected cells (cytotoxic T cells) Release cytokines which modulate activities of other cells - activate macrophages, help B cells make antibody (helper T cells)

What is the role of pattern recognition receptors?

Recognise simple molecules and regular patterns Identifying pathogens

How are tumours regulated by the immune system? How could the immune systems tumour regulation be used?

Recognised as foreign NK and cytotoxic T cells kill Tumour specific antigens = targets for vaccination + immunotherapy Work developing vaccines such as vaccinia (small pox) in treating liver tumours Also injection of BCG into some tumours has led to shrinkage

Describe phagocytosis

Recognition Endocytosis of pathogen - forms phagosome - internalisation Fusion with lysosome - phagolysosome Killing Waste - digested products released

What are the different types of epitope?

Repeat = multiple sites for recognition Unique = recognised by lots of receptors More chance for recognition and response

How does IgA get transported across the epithelia?

Requires receptor Released to gut lumen with secretory component attached Secretory component = vital, prevents degradation of antibodies 3-5g/day Secretory component: MW 70,000; made by epithelial cells & involved in transport of IgA dimers

How do MHC impact organ transplants?

Responsible for graft rejection Highly polymorphic + unique to the individual

How does immunotherapy work for rheumatoid arthritis?

Rheumatoid arthritis increases TNF alpha - swelling, joint pain, typical arthritic joints Antibody therapy against TNF alpha : monoclonal antibodies bind and prevent it being a proinflammatory cytokine - reduce in pain and clinical signs of arthritis

How does a genetic defect to the TLR5 cause UTIs?

SNIP - single nucleotide polymorphism - 10% UTI patients Reduced defensin peptide synthesis and secretion, reduced E. Coli killing Increased susceptibility to UTI Change from C to T at base pair 1174 results in STOP codon & truncated TLR5 receptor (no intracellular signalling) Intracellular part missing - no signalling, no AMP so bacteria keep growing and causing infection Uncontrolled cytokine response, only treatable by antibiotics No clearing due to no signalling - repeated antibiotics = AM resistance

What is anaphylaxis + how is it controlled?

Severe allergic reactions - IgE Fc receptors on mast cells and basophils: increase release of histamine, increase TNF alpha, increase vasodilation Use epi-pen - adrenaline - increase in vasoconstriction, increases blood glucose levels

What barriers does the body have to infection?

Skin Mucus - cilia, commensals, low pH Acid in stomach Antibacterial enzymes - lysozymes, secretory phospholipase A2 - tears, saliva + phagocytes Antimicrobial peptides (AMPs) - pores in microbes Lectins

What are MALTs?

Small concentration Submucosal tissues in intestinal and respiratory tract Respiratory: Nasopharyngeal lymphatic tissues (i.e. tonsils and adenoids), bronchus associated lymphatic tissues Intestinal MALTs: Peyer's patches, appendix and isolated follicles in intestinal mucosae Intestinal: Peyer's Patches (increase SA) found throughout ileum, appendix and isolated follicles

Describe the Lectin complement pathway

Soluble receptors (acute phase proteins) Recognises microbial surfaces activates complement cascade CHO on microbial surface Complexes of mannose binding lectin and MBL-associated serine proteases MASP-1 and MASP-2 - cleavage and activation MASP-2 then cleaves C4 and C2 Same as activated C1s Pathway then proceeds as classical Same C3/C5 convertase - just different initiation

How do T-follicle helper cells impact infection?

Stimulate naïve B cells to plasma cells When plasma cells - release more antibodies Generate class switched antibodies - IgM to other types Contributes to kills of all types of pathogens Type 1 and type 2 response

What Ig-like domains exist in other molecules?

T cell receptor MHC Cell adhesion molecules Signalling molecules

What are the T lymphocyte receptors?

T cell receptor (TCR) Binds complex of antigenic peptide + MHC Always remains anchored on cell surface - similar to antibody single arm

What is type 4 hypersensitivity?

T cells, cell mediated (type 1 diabetes, cytotoxic T cells destroy beta cells of pancreas, leads to diabetes, decreased insulin)

What are the T-cell subsets?

T-helper cells (TH1, TH2) Cytotoxic T cells - tumour cells, virally infected (CTLs) T regulatory cells - calming effect Memory T cells (TH and CTL) Natural killer T cells (not the same as natural killer cells in innate response)

What are the types of pattern recognition receptors?

Toll-like receptors, on membrane surface, 10 in humans NOD-like receptors, intracellular, nucleotide-binding oligomerization domain RIG-I-like helicases

What are the secondary organs of the immune system?

Tonsils, lymph nodes, spleen, mucosal associated lymphoid tissues (MALTs) Peripheral lymphoid tissues Lymphocytes recirculate and, if they meet antigen, undergo clonal expansion and differentiation in the tissues Circulate in fluids- blood and lymph Adaptive immune response occurs in secondary lymphoid organs

What can be the consequence of systemic inflammation?

Toxic shock When there is an uncontrolled release of molecules to infection sites

Give an example where ADCC would occur

Tumour cells - stop cancers progressing + taking over Detection by FC receptor Induces cell activation - degranulation Lyses target cells Mainly NK cells Granzymes - apoptosis Perforins - makes pores in surface

What factors impact the immune response?

Type of pathogen Localisation Stage of infection Challenge

What innate defences protect against UTIs?

Urine flow - physical factor Epithelial barrier Epithelial defensins - host antibiotic peptides

Which viral oncogenes are associated with immunodeficiency?

Viral oncogenes - hep C, HIV, herpes virus 8 - Kaposi sarcoma

How are endogenous antigens processed by MHC1?

Virus infects cell Viral proteins synthesised, in cytoplasm DNA incorporated with host cells Proteosome cleaves peptides to smaller fragments TAP transporters used to get to ER ER has MHC I for binding Transported to cell surface Cytotoxic T comes to apoptose cell

How does tuberculoid leprosy affect the body?

Walls off area of infection, lots of macrophages but bacteria evade phagolysosomes, grow and form lesions Not highly infectious - normal T cell and antibody response Infected people normally live - walling off protects Cytokines - type 1 response, macrophages for enhanced intracellular killing Less external impact

What is type 1 hypersensitivity?

allergic reaction - IgE releasing histamine

What is inflammatory bowel disease?

eg: Crohn's Chronic disease of gut intestinal mucosa 70% cases - effects distal ileum Causes gut pain and diarrhoea Inappropriate response of innate/adaptive immune system to gut microbiota Colonisation of different bacterias disrupts balance

What is haematopoiesis?

formation of blood cells - involves immune cell production occurs in bone marrow in long/pelvic bones high turnover, some stay + some removed + killed

How are leukocytes produced?

haematopoietic stem cells in bone marrow

What is type 3 hypersensitivity?

immune complex mediated - abnormal response eg: Systemic lupus erythematosus (SLE) - agglutination + complexes form, deposit at susceptible site (face) see complexes forming below skin, can cause arthritis if complexes form in joints - IgG to self and forming complexes, autoantibodies to DNA and AGs

How is leprosy spread?

nasal droplets

Where are pattern recognition receptors found?

neutrophils, macrophages, dendritic cells - host cells

How is the complement system regulated?

regulatory proteins readily break down complement proteins, minimizing host cell destruction Avoid attacking self - avoid using all components up Important = C1 inhibitor (stops classical early on, impacts MASP-2), complement receptor 1 and factor I

What are features of specific immunity?

·Clonally distributed receptors Large repertoire - low frequency of cells specific for any antigen Response takes time to develop Antigens indue effector and memory lymphocyte formation