L3- Antibody Structure, B cell Receptors and B cell development

Flashcards for Immunology and Infection Lecture 3

What type of antigens can the immune system recognize?

Epitopes on proteins, Peptide sequences from proteins, polysaccharides, lipids

What factors determine whether a substance acts as an antigen?

Foreignness, Molecular size, chemical composition and complexity, processing pathways

What is an epitope?

The specific area on a protein that an antibody or T cell receptor binds to.

What is the basic structure of an antibody molecule?

Two identical heavy chains and two identical light chains linked by disulfide bonds

What does the Fab fragment of an antibody consist of, and what is its function?

L chain plus part of the H chain and is responsible for antigen binding

What does the Fc fragment consist of, and what is its function?

Only H chain and mediates biological function

What types of disulfide bonds are present in antibody structure?

Interchain and intrachain, creates immunoglobulin-fold domains

What is the role of the hinge region in an antibody molecule?

Flexibility between the two Fab arms

What is the function of the carbohydrate groups attached to immunoglobulins?

Enhance solubility and modulate biological functions

What are the two types of light chains in antibodies?

Kappa or lambda

What are the five classes (isotypes) of heavy chains in antibodies?

Gamma, mu, alpha, epsilon, delta (G M A E D)

How do subclasses of IgG antibodies differ?

The amino acid differences between subclasses affect their biological activity, e.g., in opsonisation, complement activation, etc.

What are the regions within the variable regions of light and heavy chains that show the greatest variability?

Hypervariable regions

What role do the hypervariable regions play?

Binding to an antigen

What are hypervariable regions also known as?

Complementarity Determining Regions (CDRs)

What do framework regions provide?

The scaffold of the immunoglobulin fold

Why is variability in the amino acids in the CDRs important?

The diversity of shape in the antigen-binding site necessary for specificity

What molecules transduce signals via ITAMs in B-cell receptor complexes?

Igα and Igβ

Which molecules transmit and relay signals to the cell interior in the B-cell receptor complex?

CD19, CD81, and CD21

What mediates the activation of receptor-associated src family tyrosine kinases?

Crosslinking of BCR by antigen

What process can produce chimeric, humanized, or heteroconjugate antibodies?

Genetic engineering of antibodies

What process selects against cells expressing antibody that recognizes self?

Negative selection

Approximately how many B cells are generated per day in the bone marrow?

5 x 10^7 cells/day

What characterizes a mature naive B-cell?

Expresses IgM and IgD with the SAME antigen specificity

What occurs during gene rearrangement and expression of antibody in the Pro-B cell?

H-chain gene rearrangement

Name the three possible outcomes when surface receptors are tested against self-antigens?

Clonal deletion, receptor editing, induction of anergy

Where does central tolerance occur?

Bone marrow

What happens when self antigen binds to IgM on an immature B-cell?

Development is arrested

What receptor do T2 B cells express for the B-cell survival factor BAFF?

BAFF-receptor (BAFF-R)

What type of cells can a mature B-cell differentiate into?

Plasma cell and Memory B-cell

What are the two types of B-cell response in the periphery?

Thymus-dependent (TD) antigen and Thymus independent (TI) antigen

What type of cells is required for Thymus-dependent (TD) antigen activation?

CD4+ T cells (helper T cells)

What type of help do follicular B cells use respond to antigens?

Produce antibodies