L4 Immunoglobulins and Biology of T cells

VOCAB NOG TOEVOEGEN

Humoral immunity

The process of adaptive immunity manifested by the production of antibodies by B lymphocytes

Antibody mediated immunity

immunoglobulin

surface bound + secreted

a large group of glycoproteins that constitute the antibodies formed in response to antigenic stimuli

antibody

antigen specific secreted molecule

immunoglobulin multichain glycoproteins synthesized by B cells and plasma cells in response to the introduction of foreign substances

immunogen

induce immune responsea

antigen

can react with immune components

epitope

antigenic determinants

B cells produce … types of immunoglobulin

surface immunoglobulin

secreted immunoglobulin

Antibody structure

key and lock model

Immunoglobulin structure

1. Fab fragment, (variable part?)

2. Fc fragment

3. Heavy chain 2x

4. Light chains 2x

5. Antigen binding site

6. Hinge region

4 peptide chains, 2 heavy and 2 light chains

kept together by disulphide bridges

Immunoglobulin structure - drawn out

The hypervariable antigen binding site

Hypervariable CDRs are located on loops at the end of the Fv regions

CDR1, 2, 3

Most hypervariable regions coincided with antigen contact points - the complementarity determining regions CDRs

Variability of amino acids in related proteins

antibody molecules - there you see the CDR1, CDR2, CDR3

Digestion with the proteolytic enzyme’s pepsin and papain

isotypes

have different heavy chains

Found in all animals of the same species

All individuals have IgA, IgM, IgG, etc

allotypes

identical constant regions with minor immunologic differences

found in some but not all members of the species. Thus individuals may possess a given determinant. Antibodies can be obtained by injection of the same species which does not have the determinant. Relaed to certain diseases

Individuals have minor differences in conserved regions based on genetic differences

idiotypes

recognize different epitopes (CDR regions differ)

Antigen determinants exists of a result of unique structues generated by the hypervariable subregions (CDRs) on the L and H chains.

Determine binding repertoire

Isotypes of immunoglobulin classes

Distribution of IgM, IgG, IgA, IgE in serum and secretionsS

Anti-idotype vaccines

Antigen

Idiotype → anit-idiotype (mimic of epitope) → anit-anit-idiotype (recognizes epitope)

Affinity of an antibody

Affinity is the binding strenght of the interaction beteen epitope and an antibody’s antigen binding site

Binding strenght of a single interaction (1 single Fab fragment + 1 epitope)

[ Ag] + [Ab] ← → [Ag-Ab]

Affinity constant:

Ka = [Ag-Ab]/[Ag][Ab]

Antibody-antigen binding is reversible

Affinity is determined by

Hydrophobic bonds

Hydrogen bonds

Electrostatic bonds

Van der Waals bonds

Avidity

The accumulated strength of multiple affinities of individual non-covalent binding interactions (also called functional affinity)

avidity > sum of individual affinities

Affinity and avidity

Fab/IgG monovalent affinity

IgG/IgM multivalent avidity

Antibody production

Helper T cell → B cell → plasma cell → secreted antibodies

BCR

B cell receptor

All BCRs are Igs but not all Igs are BCRS

Results of antigen binding to BCR

Ag internalization

Entry into cell cycle

Enhanced survical (anti-apoptotic)

Increased MHC II nad costimulator expression

Increased cytokine receptor expression

B cell is efficient APC especially in priemd individuals

T-dependent antigens

T helper cell helps B cell to become fully activated

Steps to antibody production

T cell dependent activation of B cells

3 signals required for B cell activation

Antigen binding by B cell receptor = cell bound immunoglobuli

Costimulation by T helper cells

Cytokines (IL-4)

Secondary response

B cell act aslo as antigen presenting cell

B cell activation by Ag

Synergestic signals of BCR + CD19/CD21 complex (receptor for complement facto 3d) results in 100-fold B cell activation

Factor 3d is derived from complement factor C3b

M

Mechniams isotype (class) swithcing

Class swithcing from IgM to IgG

Class switching to IgA

Cytokines induce class switching/isotype switch

IgG - interferon-gamma (IFN-Y)

IgA - tumor growth factor-beta (TGF-B)

IGE - IL4, IL5, IL13

Clonal selection theory

States that a clonal expansion of the original lymphocyte occurs when the orignal lymphocyte is activated by binding to the antigen

Each lymphocyte (B or T cell) bears a single unique receptor with a specific antigen-binding site

When an antigen enters teh body, it selects (binds) only those lymphocytes wtih receptors that specifically recognize it

The selected lymphocyte proliferates (clonal expansion), producing a large populattion (clone) of identical cells, all specific for that same antigen

Some of these cells becoem effector cells (e.g. plasma cells that secrete antibodies) and other become memory cells for faster responses upon re-exposure

T cell dependent and independent antigens

T cell independent: antigen has repeating structures, often carbohydrates, eg. LPS

T cell dependnet: antigen is often protein and B cell needs T cell help

Activation of B cell by thymus independent antigen

T cell dependent and independent antigens - graph of concentration [Ab]

Features of the 2nd response

shorter latent period

prolonged Ab production

higher (IgG) Ab concentration

different isotypes

increased Ab iffinity

kinetics of the immune response

what is the role of the booster dose

How to get from a Naive B cell to a memory B cell

Differences primary and secondary response

Primary

• slow (4-7 days)

• small amounts of Ab

• IgM first

• [IgM] >- [IgG]

• Low affinity

secondary (booster)

• fast 2-4 days

• large amounts of Ab

• [IgG] > [IgM]

• high affinity

monoclonal antibodies - tests

classical method - hybridoma technique

phage display techniques - recombinant DNA

How to produce monoclonal antibodies

Phage display cycle

Functions of antibodies

opsonization

neutralization of toxins

complement activation

agglutination

blocking receptor binding

Humoral immunity

the immunity mediated by antibodiesd

ifferent Ig isotypes (classes) provide for … functions

different

different Ig isotypes have .. distributions

different, blood, secretions, mucus, saliva, tears, milk, cross the placenta

seroneutralizatoin

Circulating antibodies

Concentrations of Ab in serum (depending on species)

IgG, IgM, IgA

IgG, 0.3-29 mg/ml

IgM, 0.3-5 mg/ml

IgA, 0.1-5 mg/ml

Adaptive or innate immunity?

Circulating antibodies - forms

Specific antibodies (SpAbs)

Natural antibodies (NAbs)

Maternal antibodies (MAbs)

Natural antibodies (NAbs)

Immunoglobulins that circulate in the body without prior exposure to a specific antigen

CD5 positive B1 cells

Peritoneum

Mainly IgM, (IgG, IgA)

Low affinity

Low specificty (broad range)

No stimulaton

Antigenic triggering required?

Function of NAbs

Regulation Immune responses

• networks

• binding to cytokines, chemokines

• blocking receptors

neutralization pathogens (first line of defence)

link innate and adaptive immunity (opsonization)

Function fo maternal antibodies

Protection of young animals

Maturation immune system

• idiotypic networks

• block oral tolerance induction

• stimulate endogenous responses to gut microbiota

Adaptive immunity

The response of anitgen-specific lymphocytes to antigen, incluign the development of immunological memory

antibody

an antigen-binding immunoglobulin, produced by B-cells, that functions as the effector of an immune response

antigen

a foreign molecule that does not belong to the host organism and that elicits an immune response

B-cell

a type of lymphocyte that develops in the bone marrow and later produces antibodies, which mediate humoral immunity

complement

an immune response whereby a cascade of proteins attack extracellular forms of pathogens

Fab (fragment, antigen bindingn) region

the regions of the antibody that binds the antigen

Fc (fragment, crystallizable region):

the region of the anitbody that binds to cell receptors

heavy chain

heavy chains come in a variety of heavy chain classes or isotypes, each which confers a distinct function to the antibody

humoral immunity

the type of immunity that fights bacteria and viruses in the body fluids with antibodies that circulate in blood plasma and lymph

immune system

the name used to describe the totality of the host defence mechanism

immunoglobulin

all antibody molecules belong to this family of plasma proteins

isotype

anitbody class determined by the heavy chain

light chains

smaller of the two compents making up an antibody

memory B-cell

a clone of long-lived lymphocytes, formed during the primary immune response, that remains in a lymp node until activated by exposure to the same antigen that triggered it;s formation. activated memroy cells mount hte secondary immune response

naive B-cell

a B cell that has never bound antigen before

neutralization

when antibodies inhibit the infectivity of a virus or the toxicity of a toxin

opsonisation

the atleration of the sruface of a pathogen or other paticles so that it can be ingested by phagocytes

plasma cell

a derivative of B-cells that secretes antibodies, i.e. antibody factory

variable region

regions that contains the antigen binding site