Antibodies: Structure and Function

Question 1

Describe the bonding between antigen and antibody.

Answer 1

Involves several weak forces active over short distances

Covalent bonds are not involved

Question 2

What is the B cell receptor?

Answer 2

Located on surface of B cells

Antibodies are a secreted form of the BCR

Question 3

What is the T cell receptor?

Answer 3

Located on surface of T cells

Binds MHC molecules presenting peptide on APCs

Key in the recognition of intracellular pathogens

Question 4

What are plasma cells?

Answer 4

Activated antibody producing cells

Make antibody in germinal centers locating in the white pulp of spleen, cortex of lymph nodes or in mucosal tissue

Question 5

What is an epitope?

Answer 5

Specific antigenic determinants on molecules

A single antigen may have multiple epitopes

Question 6

Describe the structure of immunoglobulins.

Answer 6

Consists of 2 identical light polypeptide chain and 2 identical heavy polypeptide chains

An antigen combining site is the result of the interaction between a heavy and light chain variable region

Typical antibody has 2 identical combining sites

Question 7

What happens to the b cell response over time?

Answer 7

It becomes better

Mutational events occur in the antigen binding regions during the life of the B cell which give rise to higher affinity binding

This is called somatic mutation

Question 8

What two processes are responsible for generation of antibody diversity?

Answer 8

Somatic recombination - gene segment recombination during B cell development

Somatic hypermutation - mutation that occurs at high frequency in the rearranged variable-region DNA segments of antibody genes in activated B cells

Question 9

What are the five classes of antibodies?

Answer 9

IgG

IgM

IgD

IgA

IgE

Question 10

Describe the structure and function of IgM.

Answer 10

Pentamer

First antibody made in the primary response

Fixes complement

Question 11

Describe the structure and function of IgA.

Answer 11

monomeric/dimeric

Major Ig in seromucous secretions

Fixes complement and mediates phagocytosis

Question 12

Describe the structure and function of IgG

Answer 12

Secondary antibody response

Fix complement, mediate phagocytosis, cross the placenta

Question 13

Describe the function and structure of IgE

Answer 13

Found on surface of mast cells and basophils

Major role in response to parasites and allergic reactions

Question 14

Describe the struccture and function of IgD.

Answer 14

Plays a role in eliminating B-lymphocytes generating self-reactive autoantibodies

Question 15

What are isotypic differences?

Answer 15

Differences reflect AA differences which make each antibody type different (e.g. IgG from IgE)

Question 16

What are allotypic differences?

Answer 16

Slight differences in AA sequence which make IgG from one individual slightly different from IgG in another individual

Question 17

What are idiotypic differences?

Answer 17

AA differences found in the variable regions which make up the antigen combining sight

Question 18

What three secondary effector functions are associated with antibody function?

Answer 18

Neutralization

Opsonization

Complement activation

Question 19

Describe the neutralization function of antibodies.

Answer 19

Neutralize bacterial toxins or prevent bacteria or viruses from binding to cells and entering them

Immune complexes removed by the spleen

Question 20

What is antibody dependent cellular toxicity (ADCC)?

Answer 20

Antibodies provide their function by serving as a bridge between an effector cell such as an NK cell or macrophage and a target cell

Question 21

How do eosinophils kill parasites?

Answer 21

IgE bind to parasite

Eosinophils bind to the bound IgE via Fc receptors and kill via ADCC