Adaptive Immune System I & II- Exam 3 Day 7

Type II Humoral Immune Response (Antibody mediated): Specificity and Inducibility

1. Specificity and Inducibility: •DCs engulf exogenous antigen and load the processed antigen onto MHC II molecules •DCs secrete cytokines that direct the naïve CD4+ T cell to differentiate into the Th2 lineage. (Dictated by MAMPs)

Which is the correct order of events that occur when a helper T cell activates a naïve B cell? 1. Antigens processed by the B cell are displayed on the surface of the B cell via MHC II molecules. 2. Antigens bound to the B-cell receptors are endocytosed and degraded by the cell. 3. A T helper cell binds to the antigen displayed by the B cell and stimulates the activation of the B cell. 4. The B cell proliferates and differentiates into plasma cells and memory B cells. 1-2-3-4 2-1-3-4 2-3-1-4 4-2-1-3

2-1-3-4

Specificity: Heavy and Light Chain p2

2.11*10^6 different combos Additional combinations generated from: random mutations in variable regions "slipping" during recombination at VDJ and VJ junctions Estimated 10^6 to 10^8 different antibodies/BCR produced T-cell receptor produced by a similar mechanism

Antibodies are secreted by A. B-cell receptors B. T-cell receptors C. Toll-like receptors

A. B-cell receptors

Following antigen processing, an endogenous antigen is loaded onto MHC class _______ moleculeas and presented to naive ____________ T-cells. A. I; CD8 B. II; CD8 C. I; CD4 D. II; CD4

A. I; CD8

What activates an MHC class 1 cell?

APC

Opsonization

Antibodies act as a flag to components of the innate immune system. Opsonin. Bind to the FAB region and expose the FC region which can bind to macrophages. Opsonization: coating of foreign invaders w/ antibodies Baterium+Antibodies = Macrophages, neutrophils, complement Cell + Virus + antibodies = NKC NKC are activated either through the absence of MHC class 1 or antibody-dependent cell-mediated cell toxicity. Recognize FC receptor, causing them to release perforin and granzyme

Specificity: Antigens

Antigens: molecule that elicits adaptive immune response by binding TCRs or BCRs/antibodies. Name comes from Antibody Generator. T cells can only recognize/bind to proteins Antigen is a much more precise term than ligand. Antigens only bind immune receptors. Analogy—difference in using the term "people" verses "adult males" Immunogens are immunogenic. They induce both innate or adaptive immune responses or both. Antigens bind only to adaptive immune receptors.

Some viruses have the ability to evade the immune system by blocking the cell's ability to display antigens in MHC class I receptors. How would the loss of MHC class I receptors affect the immune system's response? A. It would prevent the activation of B cells. B. It would prevent cytotoxic T cells from recognizing the cell as infected. C. It would cause nonspecific activation of the B cells. D. It would prevent the activation of helper T cells.

B. It would prevent cytotoxic T cells from recognizing the cell as infected.

Which of the following vaccine types uses live but weakened pathogen to achieve vaccination? A. toxoid vaccine B. attenuated vaccine C. DNA vaccine D. inactivated vaccine

B. attenuated vaccine

MHC I molecules are produced by A. T cells only B. B cells only C. All nucleated cells D. All nucleated cells except professional antigen presenting cells.

C. All nucleated cells

Which of the following descriptions best describes an antigen? A. a receptor on an immune cell B. an immune receptor that binds to a ligand C. a molecule that can be specifically bound by a T or B cell receptor D. any type of ligand E. any type of immunogen

C. a molecule that can be specifically bound by a T or B cell receptor

Socioeconomic and political factors affect immunization rates

Children crossing the border from Pakistan to Afghanistan are given an oral polio vaccine through a program implemented by Rotary International. Polio remains endemic in just three countries—Nigeria, Pakistan, and Afghanistan—and fewer than 200 cases were reported in 2019. 1.5 million children die each year from vaccine-preventable diseaes

Measles, mumps, rubella, and varicella (chickenpox) are all viruses. What types of memory cell populations do you think will be created?

Cytotoxic T cells TH1 cells B cells

CD8 Cytotoxic T cells: Activation

Cytotoxic T cells (CD8 Tc cells) Activation of cytotoxic CD8+ T cells requires cytokine (IL2) release from effector CD4+ TH-cells. Require help from TH1 cell.

Rotavirus vaccine is given orally. Why do you think this is the preferred route of administration?

Diarreal disease- goes to mucosal cells. Natural route of infection.

Effector Cell Function: Plasma Cells and Antibody Production

Effector B cells are called plasma cells Plasma cells can secrete 2,100+ antibodies per SECOND. -Enrichment in the rough endoplasmic reticulum, so plasma cells are protein factories. -Exhausting for the plasma cells, don't last for long Terminally differentiated (cannot perform cell division) -All produced from proliferation/differentiation of activated naïve or memory B cells. -Quickly undergo apoptosis (in about 2 days), but the antibodies they secrete may last for weeks in the blood.

The smallest part of an antigen that can be recognized is an ________________.

Epitope

Inducibility: APCs

Examples of professional antigen-presenting cells (APCs) include dendritic cells, macrophages, and B cells. Dendritic cells are derived from monocytes. Not efficient killers but very good at antigen uptake. Main role is antigen presentation. -Named for long dendrite-like extensions. -Major APC

True or false: For a single pathogen, you can do both type 1 and type 2 response

False

True/False. A single plasma cell can secrete antibodies that recognize different epitopes.

False

True or false: Antigens bind to both the innate and adaptive immune receptors

False Only adaptive

How is the immune system induced?

Has to bind to epitope

What does TH1 release?

IL2

Breast milk and colostrum (early breast milk) provide passive immunity to infants in the form of _________ antibodies. IgM IgE IgD IgA

IgA

IgM

IgM: Major isotype before class-switching occurs; activation of complement Covid test- IgM vs IgE

MAMPs and PAMPS

MAMPs bind to PRRs on the APC = microbe-associated molecular pattern (e.g. LPS, flagellin, lipoteichoic acid) bind to pattern recognition receptors (e.g. Toll-like receptors, Nod-like receptors) Note: PAMPs (pathogen-associated molecular patterns) are the same thing as MAMPs. MAMPs is just a more general term since it is not just pathogens that express these microbial patterns. For example, all gram-negative bacteria will have LPS. Not just pathogens.

Negative selection

Making sure it doesn't bind to self

What does negative selection test for?

Self reactivity

Why do we need clonal deletion?

So we don't have autoreactive cells

Which cell (B or T) has to have their antigen presented?

T

What are the names of the adaptive immune cell receptors that generate specificity?

TCR and BCR

True or false: Antigens can have multiple epitopes

True

Types of Vaccines

Vaccine design •Vaccines confer protection by initiating immune memory •Antigen-specific memory T and B cells form in response to immunization •The ideal vaccine generates long-lasting immune memory without serious side effects •Different types of vaccines include •Live-attenuated •Inactivated •Subunit, recombinant, polysaccharide, and conjugate •Toxoid

What does the Fc portion of the antibody do?

binds to complement and phagocytes

monocytes can turn into

dendritic cells or macrophages

Jamal is vaccinated against varicella, also known as chicken pox, as a young child. If he has subsequent exposure to the varicella virus as an adult, what would you expect to occur? A. He would rapidly secrete much higher levels of IgM than he did after vaccination. B. He would develop varicella because vaccines only stimulate low levels of antibodies. C. His titer levels of IgG would be much higher than they were after vaccination. D. Class switching would lead to a switch from IgG production to IgM production.

C. His titer levels of IgG would be much higher than they were after vaccination.

Helper T cells

CD4 IL2 stimulates proliferation of naive/memory T cells into effector/more memory T cells. Help entire immune system.

Coreceptors

CD4 and CD8

How are CD8 cytotoxic T cells different from NK cells?

CD8 cells look for presence of MHC1 while NKC look for absence.

How are NK cells activated?

Cell + Virus + antibodies = NKC NKC are activated either through the absence of MHC class 1 or antibody-dependent cell-mediated cell toxicity. Recognize FC receptor, causing them to release perforin and granzyme

Unresponsiveness to Self: Selection

Clonal deletion •Positive selection •Tested for functional TCR/BCR •If functional, proceeds to negative selection •If non-functional, undergoes apoptosis Picture: T cell. Tested for a functional receptor. -> •Negative selection •Tested for self-reactivity •If TCR/BCR binds to self antigens, undergoes apoptosis •If TCR/BCR does not bind to self antigens, exits thymus/bone marrow and enters periphery as a naïve T cell/B cell

Inducibility: CD4 and CD8

Co-receptors (either CD4 or CD8) must also correctly interact with the MHC molecule. CD4 interacts with MHC class II. CD8 (cytotoxic) interacts with MHC class I. Activation results in cytokine expression that promotes proliferation and cell signaling

What is a cytokine? A. a type of B lymphocyte B. a class of antibody C. a type of T lymphocyte D. a small signaling peptide

D. a small signaling peptide

Cross-Presentation

DCs engulf pathogen via phagocytosis • DCs present antigen to naïve CD4+ T helper cells via MHC II molecules •DCs cross-present antigen to naïve CD8+ T cells via MHC I molecules •Activated Th1 cells secrete IL-2 to fully activate cytotoxic CD8 T cells Single APC presents antigens for CD8 and CD4 T cells. In close proximity- T cell receives its antigen and IL2 so it can go through clonal explansion

Future of Vaccines

DNA plasmid vaccines •Introduces genetic material encoding the antigen against which an immune response is sought (eg. viral glycoprotein, capsid protein, Spike protein) •Benefits include vaccine stability and ease of large-scale manufacture mRNA vaccines •Recent advances have overcome issues with the instability of mRNA and the difficulty of delivering it into cells •Currently mRNA vaccine candidates against SARS-CoV2 in clinical trials, none on the market so far. Recombinant vector vaccines •Act like a natural infection, non-pathogenic (ex: adenovirus, insert gene of interest) •Generate cell-mediated immunity, cytotoxic T cells and TH1 cells (good for viral and intracellular bacterial responses)

CDC's Recommended Immunization Schedule

Don't need to memorize Begins as early as birth- Hep B Then you get a lot more after- rotovirus, DTAP Newer ones like Human papilloma viruses, menengitis

MMR and Autism

Dr. Andrew Wakefield Lancet MMR is associated with Autism Dr. Wakefield gave incorrect information, fraudulent Lancet retracted the paper Measles has now increased- more outbreaks

Lymphocytes include A. Natural killer cells B. T cells C. B cells D. T and B cells E. All of these choices

E. All of these choices

Effector Cell Function: CD4 Helper T cells

Effector TH cells help coordinate the adaptive immune response. Upon engagement to MHC2 and antigen, it helps cytotoxic T cells and B cells (need to be activated by signals from the helper T cells)

CD4 Helper T cells

Either/or. You either have TH1 T cells or TH2 T cells. Cytokines that TH1 cell releases is inhibitory to TH2 cells, and visa-versa TH1- Type 1/Cell mediated. Release IL2 which helps with cytotoxic T cells to undergo clonal expansion. Also increase TNFa and IFg which increase phagocytosis by macrophages/neutrophils. TH2- Type 2/Humoral. Release IL4, IL6, IL10, IL14. Activate B cells to differentiate into plasma cells and secrete antibodies.

Introduction of vaccines dramatically reduced incidence of disease

Examples: Top- Polio. Spike in 1950s and 60s. Polio -> poliomyelitis. Battle between Saben (live attenuated) and Salk (inactivated), employed 2 different vaccines. Dramatic reduction Bottom- Measles Drops in the 70's

For induction and clonal expansion of a naïve CD8 T cell to occur, a naïve CD8 T cell must engage with a professional APC (e.g. dendritic cell, macrophage) presenting an MHC class I molecule loaded with its cognate antigen. This works if the pathogen infects DCs or macrophages, but how does antigen presentation occur if the pathogen does not infect professional APCs?

Exogenous pathway- engulf pathogen/debri, presents on MHC2 Endogenous pathway- assume you have intracellular infection to be able to load peptide onto MHC1 Naive CD8 T cells have to have presentation from MHC1, but not every virus/bacterium naturally effects APC.

Which portion of the antibody binds to epitope? Fab Fc

Fab

True/False. B-cells do not need TH cells because the B-cell receptors can bind free antigen.

False--the B-cell receptor can bind free antigen (antigen does not need to be presented by a MHC molecule like T-cells require), but B-cells still need the cytokines secreted from TH cells to expand and differentiate. Antigen binding to the B-cell receptor is necessary but not sufficient for B-cell activation.

True or False. CD8+ T cells are activated through TCR-binding to a specific antigen presented by the MHC II molecules on the surface of a macrophage.

False--they bind to antigen presented on MHC class I molecules. Why can CD8+ T-cells only recognize antigen presented on MHC class I molecules? Even if the CD8+ T-cell receptor were specific for antigen presented on a MHC class II molecule, the CD8+ T-cell could not bind the antigen if it were presented on MHC class II molecules. Why not?

What does positive selection test for?

Functional TCR/BCR

Type I Cell-Mediated Immune Response

Happens with viral.bacterium that is not infecting the APC 1. Specificity and Inducibility: •Within secondary lymphoid tissue, a naïve CD4+ T cell, and a naïve CD8+ T cell engage with a professional APC that is presenting its cognate antigen. Recognize slightly different epitopes. •The activated APC secretes cytokines that influence the differentiation pathway of the naïve T cells -Very important for CD4 T cell differentiation since they can differentiate into a lot of cells •Cytokine profile is dictated by the MAMPs expressed by the pathogen (which are bound through TLR or NOD-like receptors)

Specificity: Heavy and Light chain homologous recombination

Heavy chain- V(65)D(27)J(6) Light chain- VJ During B cell maturation, the variable region is randomly stitched together from one V, one D, and one J fragment and joined to a constant region using homologous recombination.

CD4 Helper T cells p2

Helper T-cells coordinate adaptive immune responses through the release of cytokines. Type of T cell- depends on cytokines released by APC Either help B cells (humoral) or T cells (cell-mediated)

About 90% of the US population is vaccinated against the measles virus, which leaves approximately 31 million unvaccinated individuals. The rate of infection in those 31 million people, however, is not the normal background rate but is instead much lower, because transmission does not occur through the vaccinated population. What is this phenomenon called?

Herd immunity

IgA

IgA: Secretory antibody present in breast milk, tears, saliva, and other secretions Mucousa

IgD

IgD: Rare; signals B cells to differentiate and secrete antibody

IgE

IgE: Associated with allergic reactions and allergies; triggers degranulation of mast cells and basophils (and eosinophils have FCe receptor)

IgG

IgG: Most abundant in blood and tissue fluids; can cross placenta and provide passive immunity; protects via opsonization, activation of complement, and neutralization

Memory

Immunological memory provides long-term protection against pathogens, with the adaptive immune system mounting a more rapid and robust response with each subsequent encounter of the pathogen. Vaccination generates immunological memory against a pathogen, allowing the individual's immune system to fight the pathogen more effectively than had the individual not been vaccinated. Secondary or tertiary response (booster etc) is better.

Do we really need an adaptive immune system since we have an innate immune system?

Individuals with genetic deficiencies in either B cells, antibodies, T cells, or both have highlighted the importance of the adaptive immune system in protecting against infectious diseases. Antibody deficiencies- prone to opportunistic bacterial infections/fungal infections B and T cell deficiencies- susceptible to opportunistic bacterial infections/fungal infections and viruses

What is the difference in the receptors? (innate and adaptive)

Innate: TLR look the same Encoded in the germline. Looks basically the same. Not many receptors Adaptive- Random receptors through recombination (splicing). Different than the germline cells. Recognition is the main difference

Types of Vaccines: Subunit, recombinant, polysaccharide, and conjugate vaccines

•Subunit, recombinant, polysaccharide, and conjugate vaccines •Consist of 1 or more protective antigens (no whole cells or viruses) •Generate immune response targeted to a key component of the pathogen- against glycoprotein for attachment, etc. -Covid 19 spike protein- essential protein for pathogen •May require several injections to produce strong immunity, multiple boosters •Stimulate antibody-mediated immunity (humoral) •Safe for immunocompromised individuals- no live pathogen Examples: pneumococcal pneumonia, Haemophilus influenzae, Hepatitis B vaccines, meningococcal disease (meningitis) Conjugated pneumococcal vaccine combines capsular polysaccharides covalently bound to a diphtheria toxoid (highly immunogenic but non-toxic)

Specificity: Structure of TCR

•TCR also consists of constant regions and variable regions •The variable region of a TCR is highly specific in the epitope it can bind

Types of Th cells

•TH1 cells: Stimulate cell-mediated response (cytotoxic T cells- intracellular infections) •TH2 cells: Stimulate humoral response (B cells, extracellular and parasitic worms) •TH17 cells: Pro-inflammatory response associated with extracellular pathogens and some autoimmune diseases •TFH cells: Stimulate B cells to differentiate into plasma cells Clonal expansion and differentiation of CD4+ T cells into TH1, TH2, TH17, or TFH cells is influenced by the cytokines released by neighboring cells.

Inducibility: Processing of endogenous antigens

Left: Proteasome digests foreign proteins present in the cytoplasm. Complex of proteases that digests foreign proteins. Peptides translocated into the ER and loaded onto MHC I molecules -> Golgi MHC I: antigen complex is transported to the plasma membrane Note: MHC I molecules present antigen to CD8 cytotoxic T cells. Every cell expresses this except for RBC. Putting antigens on here lets immune system to know it is infected. Talking to cytotoxic T cells (CD8 positive)- effector cells Happens to viral infected cells and intracellular bacterial cells

Match the following terms with their definitions or examples A.MAMP/PAMP B. Antigen C. Secondary lymphoid organ D. Primary lymphoid organ E. clonality F.immune memory G.plasma cell H.opsonization I. Fc region J.IgG K.IgM L.IL-2 M.IL-4 1.Lipopolysaccharide or peptidoglycan 2.Molecule that binds to a T or B cell receptor 3.lymph nodes or appendix 4.bone marrow or thymus 5.expansion of identical population of B or T cells 6.rational for immunization 7.effector B cell that pumps out antibodies 8.coating of microbe with antibody or complement 9.conserved region of antibody that determines isotype 10.only isotype capable of crossing the placenta 11.Major isotype before class-switching occurs 12.Induces clonal expansion of cytotoxic T-cells. 13.Promotes differentiation of B cells into plasma cells.

MAMP/PAMP - Lipopolysaccharide or peptidoglycan Antigen - Molecule that binds to a T or B cell receptor Secondary lymphoid organ - lymph nodes or appendix Primary lymphoid organ - bone marrow or thymus clonality - expansion of identical population of B or T cells immune memory - rational for immunization plasma cell - effector B cell that pumps out antibodies opsonization - coating of microbe with antibody or complement Fc region - conserved region of antibody that determines isotype IgG - only isotype capable of crossing the placenta IgM - Major isotype before class-switching occurs IL-2 - Induces clonal expansion of cytotoxic T-cells. IL-4 - Promotes differentiation of B cells into plasma cells.

Why do NK cells looks for lack of MHC class 1?

MHC class 1 is on all cells Some viruses can downregulated MHC class 1

SCID

severe combined immunodeficiency disease Neither T or B cells are created No functional adaptive immune system. If not determined prior to birth, will die quickly (first weeks of life) due to infection David Vetter- boy in a bubble. The older brother had SCID but died early. Intended to be temporary. At the age of 13, they did a bone marrow transplant but his sister had Epstein-Barr (infectious mononucleosis) so he died.

Positive selection

Making sure receptor is still functional

NK vs T cells

NK recognize via absence of MHC1. Don't have T cell receptor. T cells recognize MHC1 Early on in a viral infection- cells can downregulate MHC1 stimulating NK Can also upregualte for T cells to bind

Clonality- Naive B cells

Naïve B-cells: Released from the blood or in the secondary lymphoid tissue B cell receptors (BCRs) are NOT identical. Encounters epitope, becomes activated -> Activation -> clonal expansion: Upon BCR binding to its cognate antigen, B cell undergoes clonal -> Differentiation: Memory B cell (small subset, hangout in secondary lymphoid tissue) Plasma B cell (actively secrete antibodies)

How are highly specific TCRs and BCRs generated, with each T cell or B cell capable of recognizing a single unique epitope? Does the human genome encode for millions of genes that each give rise to a unique TCR or BCR?

No

Will most naïve T-cells bind an antigen? Yes, definitely No, probably not

No, probably not Many naive T-cells/B-cells will never "find" their antigen. Because there are so many naive B/T cells with different receptors, it takes time to find the TCR/BCR that matches the antigen in a naïve population. However, most foreign antigens will have at least one T-cell receptor (or B-cell receptor) that will recognize and bind.

Body's Three Lines of Defense

Non-specific First line- Skin, mucosa, membranes, chemicals Second line- phagocytosis, complement, interferon, inflammation, fever Specific Third line- Lymphocytes, antibodies

B/T Cell Development: Mature

Once mature (not autoreactive), B/T cells are expelled into the peripheral bloodstream as mature, naïve lymphocytes. These cells concentrate in secondary lymphoid tissues distributed around the body, ready to respond to threats. Ex: Lymph nodes, Peyer's Patch of the intestine, adenoids ___________________________________________________________________________ From the circulatory system, naïve T and B cells access secondary lymphoid organs distributed around the body. Secondary lymphoid organs include the spleen, lymph nodes, tonsil, appendix and Peyer's patch of small intestine. These specialized tissues contain dense populations of recirculating T/B cells and detain antigen to allow exposure required for the activation of these lymphocytes. Immature T cell (bone marrow & thymus) à naïve T cell (blood, secondary lymphoid organ) à effector T cell (following exposure to specific antigen and released into the body to traffic to the site of infection and mount an immune response) OR memory T cell (following exposure to specific antigen but remains in secondary lymphoid organ to await a re-encounter with pathogen) Immature B cell (bone marrow) à naïve B cell (blood, secondary lymphoid organ) à plasma B cell (effector state of B cell; following exposure to specific antigen, plasma B cells will pump out antibodies) OR memory B cell ((following exposure to specific antigen but remains in secondary lymphoid organ to await a re-encounter with pathogen; does not produce antibodies)

Plasma Cells and Antibody Production: Functions performed by antibodies

Opsonization- allows for increased phagocytosis/Complement Activation of complement cascade- C1 binds to FC portion of antibody, initiating cascade of complement. -Inflammation, opsonization, and formation of MAC complex

Vaccine Safety

Problems associated with immunization include: •Mild toxicity most common --Pain at injection site, or in rare cases, general malaise or fever high enough to induce seizures •Risk of anaphylactic shock •An allergic reaction to the vaccine (Allergy against eggs) •Residual virulence from attenuated viruses --Live attenuated disease, recent to virulent form. 1/10^6 •Allegations certain vaccines cause autism, diabetes, and asthma •Research has not substantiated these allegations

Antigen Presentation

Professional APCS: dendritic cells, macrophages, B cells Process antigen then load to MHC1 or MHC2 that are presented to naive CD4 T cells Endogenous pathway assumes that there is an intracellular infection with a virus or intracellular bacterium so the peptide can be loaded onto MHC I molecule, and CD8 cytotoxic T cells must have their first antigen presentation by a professional APC , but not every single virus or intracellular bacterium will naturally infect antigen presenting cells

During Endogenous processing, peptides are processed in the ________________.

Protesomes ER -> Golgi

Inducibility: Processing of exogenous antigens

Right: Brought to the cell from phagocytosis Phagosome binds with the lysosome, within you have digestion -MHC II molecules assembled in the ER. Invariant chain acts as a placeholder to prevent premature binding to antigen -Invariant chain is degraded once endosome with MHC II buds from Golgi -Endosome fuses with phagolysosome and antigen (digested contents) is loaded onto MHC II -MHC II: antigen complex is exported to the cell surface Note: MHC II molecules present antigen to CD4 helper T cells.

Why isn't it recommended to vaccinate against TB or anthrax in the U.S.?

Risk benefit analysis- not great risks, so benefit does not outweigh the risks

Where does antigen presentation occur?

Secondary lymphoid organs like lymph nodes

Immunological Memory: Second Response

Secondary response is faster AND stronger. This is why vaccination is effective. Memory B and T cells respond faster and with a stronger response than naïve cells.

Specificity: Structure of BCR/Antibody

Structure of BCR/Antibody •Fab regions bind antigen (fragment, antigen binding) • Variable region that determines specificity Light chains and heavy chains •Fc region (bottom of the Y) •Binds Fc receptor on phagocytes/complement Five different isotypes -Heavy chain -Bind to FC receptors on phagocytes -Opsonization -Complement proteins can bind to FC region The disulfide bonds within the chains and between them stabilize antibodies making them resistant to denaturation and proteolysis. Half-life for IgG antibodies are approximately 20 days in serum.

Specificity: TCR and BCR

T cells possess T-cell receptors (TCRs). Only around one or two recognize the epitope, but if they encounter the epitope they quickly replicate. B cells possess immunoglobulin molecules B-cell receptors (BCRs) when on the surface of a B-cell Antibody is the secreted form of the BCR. Identical to the BCR.

Specificity: Epitopes

The smallest part of an antigen that can be recognized is an epitope. Each antigen may have multiple different epitopes, each capable of stimulating a response. Picture shows antigen with multiple epitopes. Different B cells/antibodies can bind to these epitopes.

Vaccine Efficiency

Vaccine efficiency •No vaccine is 100% effective •Childhood vaccine effectiveness rates are usually 85-90% Herd immunity •In reality, you can never immunize 100% of a population...but you don't HAVE to. •If you can effectively reduce the number of susceptible individuals, an illness can't progress in a population effectively. _________________________________________________________________________ Estimating infected individuals in a population becomes a numbers game. 1,000 individuals, all vaccinated, exposed to measles virus—how many will fall ill? Now ramp this number up to a rough estimation of the population of the U.S. (375 million)—How many people might fall ill in a measles epidemic, even if we had 100% of the individuals vaccinated? Opponents of vaccination use these numbers to argue that vaccines do not work—which is a misrepresentation. Imagine if no one was vaccinated, instead.

Passive Immunization: Graph

What happens to IgM and IgG levels following passive immunization? IgM and IgG eventually go down Following active immunization? Both eventually go up, especially after boosters. Increases antibodies and memory cells.

Interaction between MHC and CD promotes ........

cytokine expression that promotes proliferation and cell signaling

Variability is found in the....

heavy and light chain Heavy: VDJ Light: VJ B cell maturation- random stitching together Homologous recombination

Types of Vaccines: Toxoid Vaccines

•Toxoid vaccines •Use a toxin produced by the pathogen to generate an immune response instead of generating the pathogen itself •Stimulates antibody-mediated immunity •May require several injections to produce strong immunity •Examples: DTaP (protects against diptheria toxin, tetanus toxin, and pertussis toxin). Not actually against bacteria, just the toxin that does damage.

Passive Immunization

•Transfer of preformed antibodies (e.g. maternal antibodies; antiserum) to provide humoral immunity against a pathogen or toxin Limitations to passive immunity: -Cannot give regularly •Antisera extracted from animals can trigger allergic reactions called serum sickness •Antibodies are degraded relatively quickly (week - 2 weeks) •Individual not protected from subsequent infections- no memory -May be contaminated with viral pathogens

Type I Cell-Mediated Immune Response- What does it respond to?

•Type I Cell-Mediated Immunity is elicited in response to: •Viral infections •Intracellular bacterial infections •Live, attenuated vaccines Ex: MMR vaccine Directly killed by T cells

Type II Humoral Immune Response

•Type II Humoral Immunity is elicited in response to: •Extracellular bacteria •Helminths (parasitic worms) •Allergens •Inactivated vaccines, toxoid vaccines, and conjugate vaccines

Vaccination (Active Immunization)

•Vaccination (Active Immunization) •Administration of antigens so that the patient actively mounts an adaptive immune response --Effector and memory population --Patient forms a population of antigen-specific B and T cells in response to the vaccine A subset of antigen-specific memory B and T cells will form and will remain in the secondary lymphoid tissue, awaiting a re-encounter with the pathogen --Population of responding antigen-specific cells increases --Memory B cells have already undergone class switching --Memory T cells have less stringent requirements for antigen presentation (activation signals), still has to find antigen

What are the main functions of antibodies?

• Inactivate toxins, recruit complement, attract phagocytes Opsonization Agglutination Prevent binding of receptors Prevent conformational changes.

Overview of Adaptive Immunity

•Adaptive immunity is the body's ability to recognize and defend itself against distinct invaders and their products •Five attributes of adaptive immunity: MUSIC •Memory •Unresponsiveness to self •Specificity •Inducibility •Clonality

CD8 Cytotoxic T cells: After activation

•After initial activation of a cytotoxic CD8 T cell by an APC, then any infected host cell can present foreign antigens from an intracellular pathogen onto MHC class I molecules. -Look for infected cells. •Upon recognition of their specific antigen:MHC I complex, Tc cells kill infected host cells the same way as NK cells do by releasing perforin (pore) & granzyme (apoptosis).

Inducibility: MHC

•Antigens bind in the antigen-binding groove of Major Histocompatibility Complex (MHC) molecules. Found during transplants. •MHC molecules function to hold and position antigenic determinants for presentation to T cells •Two classes of MHC proteins •MHC class I (present on all cells except red blood cells) •MHC class II (present on antigen-presenting cells (APCs): B cells, macrophages, and dendritic cells) Allow TCR to bind and engage

Type I Cell-Mediated Immune Response p3

•Chemotactic signals guide activated effector T cells to the site of infection -CD8 cells go through the blood, looking for site of infection •Upon recognition of an infected cell presenting its MHC I: cognate antigen, the cytotoxic CD8+ T cell will release perforin and granzyme -Releases perforin and granzyme -> killing -Th1 cells release cytokines (TNF-α and IFN-𝛄) that increase phagocytic activities of macrophages and neutrophils

Inducibility

•Five attributes of adaptive immunity •Inducibility: When a TCR or BCR binds the epitope for which it is specific, the T or B cell is induced or activated •T cells must be "presented" their epitope through a process called antigen presentation •Antigen presentation occurs in secondary lymphoid organs like lymph nodes •B cells can bind their epitope directly, without the assistance of an antigen-presenting cell

Immunological Memory

•Five attributes of adaptive immunity •Memory: During clonal expansion, a subset of memory T and memory B cells form that will remain in the body for years -Wait in secondary lymphoid tissue to re-encounter their pathogen •Memory T and B cells respond more rapidly and more robustly than naïve T and B cells Figure: Serum titer of antibodies after primary and booster vaccine.

Unresponsiveness to Self

•Five attributes of adaptive immunity •Unresponsiveness to self: T and B cells only attack foreign, non-self cells •A process called clonal deletion deletes any autoreactive cells- deletes autoreactive cells •Immature B cells undergo clonal deletion in the bone marrow •Immature T cells undergo clonal deletion in the thymus

Clonality

•Five attributes of adaptive immunity •Clonality: After induction, a T or B cell will proliferate (replicate) to form millions of identical clones of itself •Because of the specificity of T and B cells, there are very few (1 or 2) T or B cells that recognize a particular pathogen •When a threat ensues, the T and B cells specific for that threat must quickly expand and form an army of clones specific for the invading pathogen

Specificity

•Five attributes of adaptive immunity •Specificity: Tailored against a specific pathogen •Adaptive immunity recognizes specific epitopes (molecules) on a pathogen In contrast, Innate immunity is generalized; triggered by pathogen-associated molecular patterns (PAMPs), e.g. flagellin, LPS After phagocytosis, the last step is exocytosis, so contents of digested bacterial cells are released in the interstitial fluid, picked up, and carried to the lymph where B and T cells can respond. Antigen- large molecule made up of multiple epitopes. Antigen is made up of a ligand that a B or T cell can respond to. Ex: T cell able to respond to LPS, which is made up of lipid A, polysaccharide chains. Epitope: lipid portion, part of polysaccharide T cell has a constant region and variable region which has the antigen binding site. The epitope can bind to this site.

Herd Immunity

•Herd immunity is only possible for diseases that are contagious and transmitted between humans. •Estimates are that 75% of a population or more must be immunized to reduce disease through herd immunity. This varies with each pathogen -Large enough pool of immunized individuals = less hosts Herd immunity protects individuals unable to be immunized.

Types of Vaccines: Inactivated vaccines

•Inactivated vaccines •Consist of whole virus/cells that have been inactivated by heat or chemicals (formalyn- 27% formaldehyde) •Microbe cannot revert, replicate, or spread •Often contain adjuvants (chemicals added to increase effective antigenicity). Often mimic MAMPS, triggering antigen cells to release cytokines. •Drawbacks include lower/shorter stimulation of immune responses, a need for multiple injections (boosters), and greater risk of negative side effects •Examples: cholera, rabies vaccines, polio vaccine by Salk

Types of vaccine: Live-attenuated vaccines

•Live-attenuated vaccines •Composed of living (but weakened) pathogen •Tend to produce HIGH immunity because the microbe replicates in the body -Rarely causes disease •Can confer contact immunity to unvaccinated individuals- vaccinated individual can shed, family members/roommates may become infected/mount an immune response •Modified microbes may retain enough residual virulence to cause disease in susceptible individuals •Examples: MMR, chickenpox vaccines

In exogenous presenting, how does the microbe end up being presented?

1. It is brought in via phagocytosis 2. It then forms a phagolysosome 3. The phagolysosome fuses with the endosome that has MHC class 2

Clonality- T cells

1. MHC: antigen complexes are displayed on the surface of APCs within secondary lymphoid organs 2. If a naïve T cell is specific for the epitope presented on the MHC: antigen complex, then the TCR will bind with high affinity and become activated 3. A population of effector T cells and a population of memory T cells form during clonal expansion

What are the five major factors of adaptive immune response?

1. Specificity 2. Non-responsive to self 3. Inducibility 4. Clonality 5. Formation of immunological memory

Type I Cell-Mediated Immune Response p2

1. Specificity and Inducibility: (Example) •In response to IL-12 and IFN-𝛄 signals, Th1 cells secrete IL-2 •Naïve CD8+ T cells bind IL-2 via an IL-2R, inducing differentiation of naïve CD8+ T cells into cytotoxic CD8+ T cells and resulting in clonal expansion. Released into the blood to the site of infection. CD8 looks for cognate antigen presented via MHC1 on an infected cell. Once it encounters it, it releases the granzyme and perforin.

Type I Cell-Mediated Immune Response: Clonality and Immunological memory

2. Clonality and Immunological Memory: Memory CD4+ Th1 and memory CD8+ CTL cells remain in the secondary lymphoid tissue, awaiting a re-encounter with the pathogen. During clonal expansion, a population of effector T cells and a population of memory T cells form. Effector Th1 and CTLs traffic to the site of infection and elicit cell-mediated immunity. 1. CD4 and CD8 T cells receive signal 2. Undergo clonal expansion 3. Population of effector T cells and memory cells

Type II Humoral Immune Response: Clonality and Immunological Memory

2. Clonality and Immunological Memory: •Differentiate into TH2 lineage -During clonal expansion, a population of Th2 effector cells and Th2 memory cells form •Effector Th2 cells secrete the cytokines IL-4, IL-5, and IL-13, resulting in: -Activates cells to class switch •Activation of IgG1- and IgE-secreting plasma B cells •Increased contractility of smooth muscle cells •Increased mucus production -Eosinophilia- increases eosinophils B cells are APC because they express MHC2 cells. Only present antigen bound to B cell receptor because it is the only one endocytosed. Presents it to T Helper cell. Have to have helper T cells to have them turn into memory B cell and plasma cells

Type II Humoral Immune Response: . Clonality and Immunological Memory p2

2. Clonality and Immunological Memory: •For naïve B cells to be fully activated, T helper cells specific for the same antigen must engage the B cell and secrete cytokines that will drive the differentiation of the B cell into a plasma cell -B cell is professional antigen-presenting cell. 1. B cell will bind antigen in the environment, triggering receptor mediated endocytosis 2. Digested and loaded on to MHC2 molecule through exogenous presentation pathway 3. B cell can then present antigen for the TH2 cell 4. TH2 cell engages B cell, triggering TH2 cell to release cytokines to activate B cell to differentiate and undergo clonal expansion, then to class switch to IgM, IgE, IgG.

Immunocontraception

A birth control method that uses the body's immune response to prevent pregnancy Entered into the genome of the virus. Used IL4 engineered ectromelia virus. Mousepox. In the mice, it actually just killed the mouse. IL4 drives production of antibodies and suppresses cell-mediated response. Cell mediated response is necessary for controlling viral replication- involved in making Tc (cytotoxic T cells) needed for killing infected cells. Potential biological warfare? Should this research be released? Didn't go against UN biological and toxic weapons convention.

How long do plasma cells last?

A few days

Professional antigen presenting cells include A. B-cells B. Helper T-cells C. Neutrophils D. Macrophages E. Dendritic cells F. Natural killer cells

A, D, and E B-cells, dendritic cells and macrophages are all professional antigen presenting cells. What defines them as professional APCs? How do they differ from one another?

Select all that apply. What is the function of the Fc region of the antibody molecule? A. It binds complement to activate the classical pathway. B. It binds specific receptors on phagocytes. C. It binds NK cells during antibody-dependent, cell-mediated cytotoxicity. D. It binds antigen.

A. It binds complement to activate the classical pathway. B. It binds specific receptors on phagocytes. C. It binds NK cells during antibody-dependent, cell-mediated cytotoxicity.

What is the function of MHC class II receptors? A. MHC class II receptors display antigens to CD4 T cells. B. MHC class II receptors display antigens to CD8 T cells. C. MHC class II receptors display antigens to plasma cells. D. MHC class II receptors display antigens to B cells.

A. MHC class II receptors display antigens to CD4 T cells.

Select all that apply. Which of the following is an example of passive immunity? A. breastfeeding B. injection of immunoglobulin C. injection of antitoxins D. injection of an antigen

A. breastfeeding B. injection of immunoglobulin C. injection of antitoxins Antitoxins are antibodies that bind to the toxin and inactivate it. This would be a form of passive immunity because the antibodies are injected into to the individual, not produced directly by the individual themselves.

Inducibility: Antigen Processing

APCs must process antigen and load it onto MHC molecules for presentation Antigen processing occurs by different processes for endogenous and exogenous antigens. Endogenous antigens: Viral proteins, intracellular bacterial proteins, etc. Exogenous antigens: Foreign materials or extracellular pathogens engulfed and digested by phagocytes (ex. bacterial toxins, extracellular bacteria, allergens) Dendritic cells are common APCs and are found in skin and mucous membranes

What does IL2 do?

Activates cytotoxic T cells, NK cells, macrophages

Artificial Methods of Immunity

Active immunization (vaccination) •Administration of antigens so that the patient actively mounts an adaptive immune response •Patient forms antigen-specific antibodies and T cells Passive immunization •Individual acquires immunity through the transfer of antibodies •Examples: Breastfeeding; antitoxins (snake/spider) -Plasma donation for covid19

Humoral and Cell mediated

Adaptive Immune Response: Humoral immune response (antibody mediated) Cell-mediated immune response (cytotoxic T-cells) Not activated equally—depends on nature of infection

innate vs adaptive immunity

Adaptive Immunity has a slow response, is variable, has numerous highly selective specificities, and improves during the response (immunological memory)

To what host cell surface protein does HIV bind?

Affects CD4 helper T cells So they don't make B or cytotoxic T cells

Plasma Cells and Antibody Production: Functions performed by antibodies p2

Agglutination causes clumping of antigen due to antibody binding. This creates a physically larger target that is easier to phagocytize. Y shape allows it to bind to two epitopes at a time. Acts like a sweeper into a pile. Antibodies also prevent binding of receptors. Common for viral infection. Antibody binds to capsid/glycoproteins so it cannot bind. Antibodies can also prevent conformational changes. Ex: DTAP- mounting a response against toxins, which have a neutralizing effect

Evolution of adaptive immunity

All aspects of adaptive immunity are rooted in the formation of immune receptors—TCRs and immunoglobulins. Adaptive immunity is exclusive to vertebrates, but not all vertebrates. It appears abruptly in jawed or cartilaginous fish. Probably due to retrotransposons that led to the ability to perform gene rearrangements that characterizes modern immune receptors. The transposable element is thought to have invaded a germline cell in an ancestor of the cartilaginous fish and inserted itself randomly into an immunoglobulin-like precursor gene. This meant that the gene could undergo rearrangements and diversify through the descendants of the evolutionary line, leading to the formation of genes for TCRs and immunoglobulin Remnant DNA sequence from this original transposable element is still present in the genes for immune receptors and confers the ability of these genes to rearrange their DNA segments in different ways to produce an astounding number of different receptor combinations to generate matches to antigens.

What are the cells that present MHC class 1?

All except RBC

Immunity:Specificity: B cells vs Antibodies

Antibodies are secreted B cells Constant and variable region that has the antibody binding pocket. Y shaped. Can bind to two antigens at any one time. BCR is identical to antibody except it has the transmembrane domains.

Type II Humoral Immune Response: Antibody actions

Antibodies do major action in humoral response •IgG acts as an opsonin, activates complement, and neutralizes toxins and pathogen attachment proteins •IgE activates mast cell, basophil, and eosinophil degranulation

Antibodies- innate and immune

Antibodies help make innate immune system better Also, NK cells can recognize antibodies

Plasma Cells and Antibody Production: Class Switching

Antibody class-switching Use of different constant region gene segments (green) leads to different classes of antibodies. Each class has slightly different structures and functions in immune responses. 5 possible types Isotypes IgG IgA IgM IgD IgE Antibodies begin as IgM BCR go through class switching, allowing the IgM to be swapped out. Each FC chain elicits a new immune response.

What are the cells that present MHC class 2?

Antigen-presenting cells (APCs): B cells, macrophages, and dendritic cells

B/T Cell Development: Immature

B and T cells originate in the bone marrow. -T cells migrate in a still immature stage to the thymus for further development. -B cells mature in bone marrow. During B/T cell maturation, gene rearrangements produce a very large number of unique BCRs and TCRs. -Rearrangements occur only in B/T cells—not germline cells. -Only 1 or two B/T cells recognize the specific antigen, but the immune system is equipped to quickly increase these numbers -The receptors are formed BEFORE exposure to pathogens! The randomized rearrangement of TCRs and BCRs enhances the diversity of microbes to which a T cell or B cell can respond and it increases the chance that a T cell or B cell will be able to mount a specific response against a pathogen. Has to go through clonal deletion process to make sure it didn't give rise to an autoreactive cell Adaptive immunity cannot be inherited.Each individual's immune system must be "trained" to build immune memory against the pathogens in which the individual encounters.

T cells bind to .....

protein

Which type of cellular receptor can bind directly to free antigen? A. T cell B. B cell C. Both D. Neither

B. B cell

Which of the following characteristics are associated with helper T cells? Select all that apply. A. Eliminate cancer cells B. Express CD4 C. Bind to antigen presented on MHC I D. Activate B cells E. Express CD8 F. Bind to antigen presented on MHC II G.Kill infected host cells

B. Express CD4 D. Activate B cells F. Bind to antigen presented on MHC II

What do granzymes do? A. Granzymes allow for the activation of helper T cells. B. Granzymes stimulate cell death in infected cells. C. Granzymes allow for the activation of B cells. D. Granzymes allow for the activation of cytotoxic T cells.

B. Granzymes stimulate cell death in infected cells.

Influenza virus would undergo ______________ antigen processing while E. coli would undergo ____________________ antigen processing. A. endogenous; endogenous B. endogenous; exogenous C. exogenous; endogenous D. exogenous; exogenous

B. endogenous; exogenous

Autoimmune diseases

Breakdown in negative selection