Antibody-Mediated Effector Functions

What are the first antibodies made by B Cells?

IgM and IgD

What antibodies do B cells make once activated in germinal centers?

IgA, IgG, and IgE

Where is IgD located?

Primarily membrane bound

IgM forms what multimer form with how many antigen binding sites?

Form pentamers with 10 antigen binding sites

IgA forms what multimer form with how many binding sites?

Can be monomeric with 2 binding sites or dimeric with 4 binding sites

Multimeric IgA and IgM are associated with that that helps them with what?

A J (joining) chain that helps with transportation through epithelial cells

Mucosal epithelial cells have what that binds J chain?

Specialized polymeric immunoglobulin receptors (pIgRs)

Camelids also make IgG2 and IgG3 subtypes. Why are they different from normal IgG?

They do not have light-chains

Where is IgG located?

Blood and tissues. Readily escapes blood vessels.

Where is IgM located?

In the blood due to its size as a pentamer

Where is IgA located (monomeric and dimeric)?

Monomeric in blood and extracellular fluid

Dimeric on mucosal surfaces

Where is IgE located?

Surfaces of mast cells, basophils, eosinophils

What is the functional role of the variable regions (Fv) of antibodies?

Neutralization by blocking binding of pathogens and toxins to their host cell receptors

What antibodies are typically neutralizing?

IgG, IgA, IgM

What are the functional roles of the constant regions (Fc)?

Opsonization, Complement activation, antibody-dependent cellular cytotoxicity (ADCC), mast cell degranulation

What antibodies are opsonizing?

IgA and IgG

How do antibodies activate complement?

Fc on antibodies bind to C1q

What antibodies trigger complement (via the classical pathway)?

IgM and IgG

What do NK cells express that binds antibodies?

FcγRIII (CD16) receptor

What antibody binds to NK cells to trigger ADCC?

IgG

What do Mast Cells express that bind antibody?

FcεRI and FcγRIII receptors

Most IgE in the body is what?

Bound to Fcε receptors

Mast cell degranulation mechanism

IgE bound to surface by FcεRI and FcγRIII receptors bind antigen

Antigens cross-link, activating mast cell to release its granules

What substance are in mast cell granules?

Vasoactive substances