Antibody structure and function II

What does the C region domains at the carboxyl-terminal portion of the heavy chain mediate?

Biological effector function

What do differences in the various heavy chain constant region domains determine?

1. Antibody half-life

2. Distribution (where antibodies can go)

3. Complement-fixing ability

4. Fc receptor binding

What is the carboxyl terminal domain of membrane bound and secreted antibody different in?

Structure and function

Are different classes of membrane bound immunoglobulin molecules are expressed by B cells at different stages in their development?

Yes

Do antibodies only survive for a limited time?

Yes they do

Where is IgG found? What is it passed onto?

In the gut and it is passed onto infants via the placenta

How many Fab fragments do antibodies have? What are they? What is the Fc portion?

Two Fab fragments. V1 and C1 of the heavy chain and V1 and C1 of the light chain. Fc is the tail portion of the antibody (C2 and C3 of the heavy chain)

What are the two enzymes that can cleave IgG molecules into specific fragments? What specific fragments?

1. Papain

2. Pepsin

Can separate the tail portion from the antigen binding site

What happens in papain mediated digestion of an IgG molecule?

It yields two identical Fab fragments (are not held together) and 1 Fc fragment

What happens in pepsin-mediated digestion of an IgG molecule?

It yields a divalent Fab fragment (both Fab are still held together) and a Fc fragment. It cuts right below the disulfide bonds.

What does Fab and Fc stand for?

Fragment antigen binding and Fragment crystallizable

What happens if you reduce the chains with mercaptoethanol? What is it good for?

All the chains are released from one another (2 heavy chains and 2 light chains). It is a good way to break up everything without using enzymes

Are antibodies immunogenic? When is an antibody response produced? What is an epitope?

Yes and when injected with another species. It is the portion of the antibody that the antigen binds to.

Where are isotopic epitopes located?

In constant regions and define heavy chain classes/subclasses and light chain types/subtypes within a species.

What are allotropic epitopes?

They are located in constant regions and may vary from individual to individual. (are between individuals)

What are idotypic epitopes?

They are located within heavy and light chain variable regions (both hyper variable and framework regions) and are defined by the unique amino acid sequences that determine specificity

Is determinant a synonym for epitope?

Yes

Can an antibody be made against another antibody?

Yes

If you put antibodies from an individual in a different individual, what is the result?

Idiotypic, isotypic, and allotypic determinants

What are the five immunoglobulin effector functions?

1. Opsonization

2. Complement activation

3. Antibody dependent cell mediated cytotoxicity (ADCC)

4. Transcytosis

5. Induction of mast cell degranulation

Describe the opsonization immunoglobulin effector function

Interactions of antibodies with Fc receptors on phagocytes promotes phagocytosis

Describe the complement activation immunoglobulin effector function

Antibody-mediated activation of complement is responsible for the inactivation/removal/killing of pathogens

Describe the ADCC immunoglobulin effector function

Antibody (IgG) acts as a receptor to enable recognition and killing of target cells by natural killer cells with Fc receptors (CD16)

Describe the transcytosis immunoglobulin effector function

Passage of antibodies across epithelial layers delivers certain classes of antibody (primarily IgA) to mucosal surfaces. It traps microbes ingested and get across the gut epithelial

Describe the induction of mast cell degranulation immunoglobulin effector function

This function is initiated by Fc receptors for IgE

What do NK cells have?

A Fc receptor called CD16 that can bind to IgG

What happens if NK cells come across a host cell coated with antibodies?

It will kill via ADCC. The NK cell can degranulate onto the cell and induce it to undergo apoptosis

What is IgE made against?

Dust and pollen

What do mast cells have? What are they used for?

Fc receptors for IgE. Fight parasitic infections but sometimes they get confused with dust and pollen.

What happens when IgE binds to its cognate antigen?

It will degranulate and you get all the allergy symptoms

What are NK cells good at killing? What happens once they get coated with IgG?

Virally infected and tumour cells. It will bind to an IgG receptor (Fc gamma) and will kill it via ADCC

What can agglutination of a particulate antigen be taken up by? What does it prevent?

A phagocyte or red blood cells that can take it to the spleen that transfers it to a macrophage. It prevents binding to cells and enhances clearance

What happens if an antibody coats the cell (neutralization of pathogens and toxins?

It can prevent entry of that cell that is necessary for infection or it causes steric hinderance and cannot bind to the cell.