Dec 11 - Antibodies and Ab Diversity

Question 0

One Light chain is bound to one heavy chain via:

Answer 0

Disulfide bonds or non-covalent interactions.

Question 1

All antibodies have the same 4 basic poly peptide chains:

general

Answer 1

2 Heavy and 2 Light

Question 2

The Fab region of an antibody is composed of ____ and ____ that make up the binding site for Ag

Answer 2

VH and VL; variable heavy and variable light

Question 3

2 _____ domains from the Heavy chains form the hinge region, which gives flexibility to the Ab’s Fab region.

Answer 3

CH2 domains

Question 4

The Fc region of an antibody, (fraction crystallizable) determines:

Answer 4

The effector function of the Ab.

These functions can include complement mediated lysis…or binding to mast cells or nuetrophils via FC-receptors (FCRs)

Question 5

The Valance of an Ab refers to:

Answer 5

The number of antigenic determinants it can bind. for membrane bound Igs, (which have 2 Fab regions) the valance is 2; one antigen for each Fab region (2 copies of the same antigen). AKA these are “divalent”.

Secreted Abs may have valances other than 2.

Question 6

The effect of valance combined with affinity is referred to as:

Answer 6

Avidity; this means that if an antigen dissociates from Fab, if another Fab is close by (i.e. high valance), it will immediatley pick up the antigen. Thus, high valance + high affinity contribute to high avidity.

Question 7

Plasma cells are differentiated ____ cells that __________________

Answer 7

B cells, that secrete and synthesize Abs

Question 8

Which antibody class is most abundant in blood, responding to most blood-borne antigens? This is also the only class that can cross the placenta to provide ‘passsive humoral’ immunity to the fetus.

Answer 8

IgG is the most abundant in the blood!

There are four sublasses, IgG1, IgG2, IgG3, IgG4

Question 9

What determines the differences in IgG subclasses?

Answer 9

Slight differences in the H chains, which correspond to differences in their functions.

Question 10

IgM:
Is found on the surface of ____ _____ Cells and is expressed as a BCR.
In the blood, it forms a _________ held together by disulfide bonds.

Answer 10

Naive B cells

Pentamer

Question 11

“J chain” protein is essential to the function of IgM because it:

Answer 11

enables the polymerization of the penatmer in IgM’s secreted form.

Question 12

The first Ab produced in an immune response is:

hint - It has high avidity…high valence + affinity

Answer 12

IgM - it has a valence of 10, so despite having lower affinity binding sitesm its avidity is very high, making it an efficient first response.

Question 13

IgA is mainly present in: __________ where it exists as a _________
In serum it exists as a _________

Answer 13

IgA is mainly present in external secretions (colostrum , milk, saliva) where it exists as a DIMER.

In plasma it is a monomer.

Question 14

Which Ab class is the first responder to microbes in mucosal surfaces?

Answer 14

IgA

Question 15

In addition to the 2 H and 2 L chains, Ig____ contains polypeptide chains SC (Secretary component) and J chain.

Answer 15

IgA

Question 16

Secratory component polypeptide of IgA is involved in what process?

Answer 16

Transepithelial transport and stabilization.

Question 17

Naive B cells express both Ig___ and Ig____, which work to internalize antigen that are bound.

Answer 17

IgM and IgD**

Note that these are both specfic for the same antigen, NOT two different Ags

Question 18

Ig____ plays a significan role in acute inflammation, protection from worms, and in antibody mediated allergy.

Answer 18

IgE

Question 19

IgE functionss by binding to _____ receptors on ____ Cells that are specific for the IgE ____ domain.

Answer 19

Fce receptors (FceR1)
Mast cells
Fc domain

Question 20

Mast cell histamine release is associated with Ig_____ / antigen crosslinking

Answer 20

IgE

Question 21

Define: isotype

Answer 21

Refers to the sequence of the constant region of the H and L chains. For H, there is G, D, M, A, and E.
For L , there is kappa and lambda

Question 22

Define: allotype

Answer 22

refers to the inherited differences in the AA sequencce of an H or L chain (within one isotype). For example, an IgM with a single AA change, but with all other AAs the same in IgM if that species.

Question 23

Define - -Idiotype

Answer 23

Unique antigenic determinants that make up the antibody combing site. ( All Abs from a B cell will express the same idiotypes, and thus bind the same antigens.

Question 24

In the generating Ab diversity, the process of Ig rearrangement occurs when:

Answer 24

a single V exon next to and ligated with a Diversity exon and Joining exon. (Forms the VDJ sequence…which specifies CDR3-complementarity determining region 3)

Question 25

The H chain isotypes comprise ____# functional C region genes:
(Bonus* what are they)

Answer 25

9

mu, delta, gamma 1-4, epsilon, alpha 1-2.

Question 26

What ware RAG1 and RAG2

Answer 26

Recombination activating genes - these enzymes are expressed by developing lymphocytes to break and rejoin DNA during translocation, contributing to Ab diversity.

Question 27

Diverisfication of the Ab repotoire:

At the DNA level (Antigen independent) there are 4 general mechanisms:

Answer 27

1. Many different families of the V regions which encode different AAs for the H and L chain
2. Many random combinations of V D and J and V/J segments.
3. “imprecise joining” of V D and J segments - (Junctional diversity) translocations a V segments can keep the last 3 nucleotides, or replace the last one.
4. P and N diversity - additional junctional diversity is contributed by addition of nucleotides by TdT enzyme

Question 28

Antigen independant diversity to Abs contributed ta the protien level is accomplished by:

Answer 28

pairing different combos of L and H chain for different B cells

Question 29

DESCRIBE AFFINITY MAATURATION

Answer 29

Ligation of BCR on B cells in germinal centers induces somatic mutations in Ig V regions. ->
Nucleotide mutations in V domain change the specificity of the Ag (can increase or decrease the affinity) ->
B cells that increase the affinity for the antigen will compete more efficiently

Question 30

describe allelic exclusion:

Answer 30

Following VH or VL gene rearrangement, there is ACTIVE SUPPRESSION of further rearrangement.

At the protein level, this means that a if there is a bad rearrangment, the process will retry on a second attemptl; BUT if there is a successful rearrangement on the first try, the suppression prevent the process from continuing.

Question 31

Abs produces by a plasma cell (DO/DO NOT) become associated with the membrane because:

Answer 31

DO NOT - Abs in plasma cells are sereted because the transmembrane domain of the H chain is spliced out.

Question 32

In Ab synthesis, H and L chains combine in the :

Answer 32

ER

Question 33

The first Ab produced on the surface of a B cell is:

Answer 33

IgM

Question 34

A mature, naive B cell is one that is:

Answer 34

Ready to respond to Ag

Question 35

Explain differential splicing in B cell development:

Answer 35

This is the mechanism that allowa a mature niave B cell to produce both IgM and IgD that are specific for the same Ag.
The primary transcript that includes DNNA from the VDJ region is spliced to yeild two mRNAs, one for IgM H and one for IgD H

Question 36

Isotype switching is:

It is accomplished by:

Answer 36

Isotype switching is the ability to associate the specificity of the Fab region (VDJ + VJ) with other isotypes of H.

It is accomplished via T-dependant antigens in the germinal center, and mediated by IL4 INF gamma and TGF Beta

Question 37

In B cell differentiation, the surrogat e Light chain functions to:

Answer 37

Stop thhe rearrangment of H chain loci and begin the rearrangement of L chain genes.

Once the L chains are complete, a functional IgM complex can be expressd on the cell.

Question 38

BCR Complex:
Inclusion of CD 21 CD 19 and CD81 result in :
Ab:Ag complexes that engage CD 32 :

Answer 38

cd21, 19 and 81 result in B cell activation

CD32 will tur down BCR signalling and limit B activation.

Question 39

CD21 can signal to CD 19 and CD 81 to influence B cell Activation. CD 19 and 81 are able to do this by influencing the strength of the:

Answer 39

Ig(alpha) and Ig(beta) complexes.

Question 40

What is the result and treatment for CD 19 deficiency?

Answer 40

Increased bacterial infection due to decreased BCR signalling
the treatment is intravenous immunoglobulin which provides passive immunity for the half life of antibody.

Question 41

WHat is receptor editing and why is it important to B cell tolerance?

Answer 41

Receptor editing is when a B cell will undergo L chain recombination to produce a new L chain with new specificity.

This is important because it occurs so that B cells can change receptors if they are auto reactive (binding self molecules) so that they are no longer ind self.