immuno 3: antibodies

What is the primary effector function of B cells?

Production of antibodies; plasma cells act as antibody factories.

What are antibodies also called?

Immunoglobulins (Ig) or gamma globulins.

What are the two forms of antibodies?

Membrane-bound (BCR) and secreted antibodies.

What is a BCR? Key structural difference between BCR and secreted antibody?

A membrane-bound antibody on B cells that recognizes antigen.

BCR has a hydrophobic membrane tail; secreted form lacks it.

Do naïve B cells secrete antibodies?

No, they express BCRs but do not secrete antibodies.

When do B cells begin secreting antibodies?

After antigen encounter and activation → differentiate into plasma cells.

What is the role of BCR?

Initiates B cell activation upon antigen binding.

What is the basic structure of an antibody? How are chains arranged?

Y-shaped molecule with 4 chains: 2 heavy + 2 light chains.

Identical heavy chains + identical light chains linked by disulfide bonds.

What regions do heavy and light chains contain?

Variable (V) and constant (C) regions.

What determines antigen specificity?

What determines antibody function?

Variable region.

Constant region.

Are light chains identical within an antibody?

Yes, both LCs are identical.

Structure of light chains?

One variable (VL) and one constant (CL) region.

Where are variable regions found?

On both heavy (VH) and light (VL) chains.

What characterizes the variable region?

High sequence variability between antibodies.

Size of variable region?

First ~110 amino acids of the chain.

What forms the antigen-binding site?

Variable regions of both heavy and light chains.

What defines the constant region?

What regions exist in constant domains?

Relatively conserved within an isotype.

CH (heavy chain) and CL (light chain).

What are antibody isotypes? What determines isotype function?

Different classes with distinct functions.

Heavy chain constant region. CH chain

Major antibody isotypes?

IgG, IgA, IgM, IgE, IgD.

How many CH domains do isotypes IgG, IgA, IgM, IgE, IgD. have?

IgG, IgA, IgD = 3; IgM, IgE = 4.

Why do CH domains matter?

They influence antibody function. characteristics

What experiment identified antibody regions?

Papain enzyme digestion of an antibody→ 2 Fab + 1 Fc fragments.

What is Fragment antibody- Fab? What is Fragment crystallizable- Fc?

Fragment that binds antigen.

Fragment that mediates effector functions.

Function of Fab region? How many Fab regions per antibody?

Binds antigen.

two.

Is a Fab the same as the variable region?

Can Fab interact with effector cells?

No; Fab includes the variable regions plus part of the constant region, so it is larger than just the variable region.

No.

Does Fc bind antigen? Function of Fc region?

No.

Binds Fc receptors on phagocyte→ opsonization by phagocytes.

Where is the hinge region located? Function of hinge region?

Between CH1 and CH2 of heavy chain.

Provides flexibility for antigen/epitope binding at different angles.

Which isotypes have hinge regions?

IgG, IgA, IgD. GAD

Do isotypes affect antigen specificity?

No, specificity is determined by variable region.

Why are multiple isotypes important?

Provide protection in different locations and ways.

Key features of IgM?

First/default antibody produced; monomer in BCR, pentamer in serum; BCR on naïve B cells.

HC Ch sequence very between stereotypes but….

are identical within the isotype

Functions of IgM?

Complement activation + BCR role.

Key features of IgD?

Mainly BCR on naïve B cells; very little secreted.

Key features of IgG?

Most abundant in tissues; crosses placenta.

Functions of IgG?

Gack of all trades. Opsonization, complement activation, neutralization, ADCC. crosses placenta!!

Key features of IgA?

Found in mucosal secretions; often dimer.

Functions of IgA?

AAAAchoo. Neutralization and opsonization; protects mucosal surfaces. Breast milk!

Key features of IgE?

Binds mast cells, basophils, eosinophils.

Function of IgE?

Mediates allergic responses. parasites. AllergEEEEEEEs.