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.