T cell and B cell Cross-Talk

Question 1

When a naive B cell recognizes its monovalent antigen, it loses expression of ____ and upregulates ____.

Answer 1

When a naive B cell recognizes its monovalent antigen, it loses expression of CXCR5 and upregulates CCR7 and MHCII.

This targets it to merge with the T cell zone and to display its antigen on pMHCII.

Question 2

Germinal centers include. . .

Answer 2

T follicular helper cells, activated B cells, and follicular dendritic cells

Question 3

BCR signaling

Answer 3

Question 4

CR2

Answer 4

A complex of 3 proteins (including CD19 and CD81) on the B cell membrane. Detects C3d, which acts as a second signal for B cell activation.

Question 5

Unconjugated toxin vaccine

Answer 5

Question 6

If a T cell sees its antigen being presented by a B cell, both it and the B cell will lose expression of ____ and gain expression of ____.

Answer 6

If a T cell sees its antigen being presented by a B cell, both it and the B cell will lose expression of CCR7 and gain expression of CXCR5.

This brings the B cell and T cell back to the follicular zone to form a germinal center, leaving behind an extrafollicular focus made up of short-lived plasma cells.

Question 7

What ultimately controls which heavy chain isotype a class-switching B cell will switch to?

Answer 7

1. Whether or not it has switched before (which regions are left?)
2. Which S region AID introduces a uracil into

Question 8

B cell selection within the germinal center

Answer 8

Question 9

Part of the reason that secondary responses result in greater antibody production is because ___ is more readily obtained.

Answer 9

Part of the reason that secondary responses result in greater antibody production is because Helper T Cell help is more readily obtained.

Question 10

At the end of a secondary antigen challenge, there are more ___ and ___ than at the end of the primary challenge.

Answer 10

At the end of a secondary antigen challenge, there are more antigen-specific plasma cells and memory B cells than at the end of the primary challenge.

Question 11

Extrafollicular focus

Answer 11

Created when a T cell recognizes its antigen on an antigen-loaded B cell in the T cell zone of an SLO.

Represents a proliferation of short-lived plasma cells stimulated by the T cell before it and the B cell progeny exit to form a germinal center in the follicular zone.

Question 12

What does CD40L/CD40 + cytokine induced signaling do to the B cells?

Answer 12

Question 13

Only ____ respond in a primary antibody response.

Answer 13

Only Naive B cells respond in a primary antibody response.

Question 14

mIg

Answer 14

Monomeric transmembrane form of IgM present in naive B cells. May also be IgD.

Question 15

Phases of B cell response

Answer 15

Question 16

Commencement of T cell / B cell interaction

Answer 16

Question 17

BCR structure

Answer 17

Question 18

B cell second signals

Answer 18

Question 19

Isotype class switching in a B cell

Answer 19

Question 20

Important outcomes of germinal center action

Answer 20

1. Heavy-chain class switching
2. Affinity maturation
3. Long lived plasma cells
4. Memory B cells

Question 21

Characteristics of primary and secondary antibody response

Answer 21

Question 22

Unconjugated polysaccharide vaccines

Answer 22

Question 23

S and C sites in Ig locus

Answer 23

S = switch site, the regions at which the germline may recombine in order to switch constant regions.

C = constant site, the coding region for the constant chains of antibodies. Each has an associated S site just 5’ of it.

Question 24

Common conjugate vaccines

Answer 24

Question 25

T-independent antigens

Answer 25

Non-protein antigens which may activate B cells without the aid of T cell help by crosslinking many BCRs.

Polysaccharides are good examples.

Question 26

Proteins involved in germline B cell isotype class switching

Answer 26

1. AID (creates a kink in the targeted S site)
2. Double strand repair machinery (recognizes breaks in previous and current S site, deletes both strands, and recombines)

Question 27

Antigen is delivered to lymphoid organs via ____.

Answer 27

Antigen is delivered to lymphoid organs via antigen presenting cells AND in cell-free form via the lymphatics.

This is why the immune system resides in the lymphatics

Question 28

Role of FDCs in the germinal center

Answer 28

Display the antigen for the developing B cells to use as a substrate for evolution.

Question 29

Toxin-conjugated polysaccharide vaccine

Answer 29

Question 30

Primary and Secondary Antibody Response

Answer 30

Question 31

Role of FcγRIIb

Answer 31

Question 32

In a secondary challenge, ___ are activated to mount an antibody repsonse.

Answer 32

In a secondary challenge, plasma cells, memory B cells, AND naive B cells are activated to mount an antibody repsonse.

Question 33

Polyvalent vs monovalent BCR binding

Answer 33

Question 34

Activation induced deaminase (AID)

Answer 34

Activated in B cells by CD40 binding. Catalyzes the conversion of cytosines to uracils in the B cell germline, triggering DNA repair. This enables the B cell’s special DNA repair system, which creates small mutations in the V site that act as fodder for natural selection. It also helps trigger heavy-chain switching.

Question 35

T follicular helper / B cell interaction at the Germinal Center

Answer 35

Question 36

Naive B cell activation begins when. . .

Answer 36

A naive B cell encounters its antigen in a cell-free form or on the surface of a macrophage in the follicles of a SLO.

Question 37

Downstream BCR signaling

Answer 37

Question 38

AID activity

Answer 38

Question 39

Initiation of T cell / B cell interaction

Answer 39

Question 40

Equivalents in BCR/TCR signaling

Answer 40

TCR / BCR

Lck / Fyn

ZAP-70 / Syk

Question 41

Summary of B cell responses to antigen

Answer 41

Question 42

Somatic hypermutation

Answer 42

Triggering of AID to create uracils within targeted regions of DNA, then activation of nonhomologous double-stranded repair to replace these lesions imperfectly.