Selection & function of antibodies

Question 1

How does activated B-cells improve specificity?

Answer 1

Through somatic hypermutation and affinity maturation.

Question 2

Antibody function: Fab dependent

Answer 2

Neutralisation of pathogens eg. by blocking viral receptors.
Neutralisation of toxins by irreversible binding

Question 3

Pro/cons with long hinge regions

Answer 3

Flexibility to better bind Ag, complement, Fc-gamma receptors and transport receptors.
/ Higher susceptibility to degradation

Question 4

Antibody function: Fc dependent

Answer 4

Opsonization, activation of complement, diffusion to extravascular sites.

Question 5

Affinity maturation

Answer 5

Centrocytes die unless they bind CD40L on a cognate TFH cell. Higher affinity is selected for in competition with other centrocytes

Question 6

Can isotype switch occur more than once?

Answer 6

Yes, but only one way.

Question 7

AID mode of action i isotype switching

Answer 7

AID nicks the switch regions , which causes a DNA bend and loops out the region between the nicks, causing a different heavy chain constant region to be downstream to the heavy chain variable region.

Question 8

Binding of CD40L happens because of…

Answer 8

When a centrocyte binds antigen hold by FDC, which causes internalisation and presenting to a cognate TFH cell.

Question 9

Which cell direct B cell differentiation and how?

Answer 9

Cognate TFH cells. By secreting either IL-10 (plasma) or IL-4 (memory) depending on cytokine microenvironment when TFH cell got activated.

Question 10

Best isotypes for toxin neutralisation and why

Answer 10

IgG & IgA because they are small for diffusion, have undergone affinity maturation. IgG is specifically transported to tissues.

Question 11

Memory cells

Answer 11

High affinity, class-switched surface Ig, don’t secrete soluble Ig.

Question 12

IgA isotype switch is induced by

Answer 12

TGF-β

Question 13

Antibody function: Opsonization

Answer 13

Antigen with IgG bound fix C1q, resulting in C3b deposition on both Ab and Ag.
C3b are picked up by erythrocyte CR1 and brought to a professional phagocyte.

Question 14

Centrocytes, centroblasts; which are expressing surface IgM?

Answer 14

Centrocytes.

Question 15

Isotype switching

Answer 15

Switching of constant regions in heavy chain.

Question 16

Antibody function: Complement activation.

Answer 16

Depends on antibody hinge-region to bind C1. IgM and IgG3 (long, flexible hinge) are good at binding of the multiple sites of C1.

Question 17

What takes place in the light zone

Answer 17

Affinity maturation, isotype switching, differentiation

Question 18

IgE isotype switch is induced by

Answer 18

IL-4

Question 19

The 2 survival signals for centrocytes are:

Answer 19

1. Binding of antigen on FDC

2. Binding to CD40L on cognate FTH that recognises that processed antigen.

Question 20

Switch region

Answer 20

Short DNA sequence preceding each heavy-chain constant region segment. Works to increase transcription before the segment, leaving the single-stranded DNA vulnerable to AID.

Question 21

Which cell directs isotype switching?

Answer 21

TFH effector

Question 22

What happens if a memory cell bind Ag?

Answer 22

Cloning and differentiation into plasma cells, outnumbering the original memory cells.

Question 23

Plasma cells

Answer 23

Don’t express BCR, MHCII. Can’t grow, hypermutate or switch isotype. Secretes alot of soluble Ig.

Question 24

When do B cells express AID?

Answer 24

As centroblasts and centrocytes

Question 25

B cell differentiation

Answer 25

Differentiation of B cells into either plasma cells or memory cells

Question 26

IgG isotype switch is induced by

Answer 26

INF-γ