B-Cell Immunity

Question 1

What are the two types of responses to antigen when B cells are activated?

Answer 1

1-Thymus-dependent antigen (most common, response against a protein)
2-Thymus-independent antigen

Question 2

What are the two types of Thymus-independent antigen?

Answer 2

1-TI-1 (multivalent, polymerized antigens recognized by PRR)

2-TI-2 (highly repetitive antigens bound by the complement C3d)

Question 3

What are the 3 signals involved in B cell activation? Which 2 are required?

Answer 3

1-Antibody crosslinking-activation
2-Co-receptor signaling- survival and proliferation
3-Cytokine-differentiation

Question 4

The clustering of antigen receptors allows what?

Answer 4

Receptor-associated kinases to phosphorylate ITAMs. Syk binds to the doubly phosphorylated ITAM to be activated

Question 5

What are the 3 components of the B cell co-receptor complex?

Answer 5

1-Complemment receptor 2 (CR2) (Binds iC3b and C3d)
2-CD19 (signaling arm)
3-CD81 (localizes complex within plasma membrane

Question 6

What are the 4 main sources of co signaling?

Answer 6

1-B-cell co-receptor complex
2-TLRs
3-CD40
4-Cytokines

Question 7

Which cells are stromal cells, cause B cell development and activation, have complement receptors, accumulate antigens on their surface to display to B cells but lack phagocytic capacity?

Answer 7

Follicular dendritic cells

Question 8

How and where are cognate pairs formed?

Answer 8

Antigen-activated B cells present antigen to effector Tfh cells at the follicle boundary between the primary follicle and T cell area

Question 9

ICAM binds LFA-1 to loosely bind a T cell to a B cell. What B cell surface protein then induces survival and proliferation?

Answer 9

CD40

*B cell then differentiates into plasma or memory cell. Can also undergo isotype switching in the germinal center

Question 10

What are the two stages (and locations) of B cell differentiation into plasma cells?

Answer 10

1-Primary focus (medullary cords)

2-Secondary focus (primary follicle)

Question 11

Proliferation of IgM secreting B cells for several days driven by IL-5 and IL-6 is typical of what stage of B cell differentiation to plasma cells?

Answer 11

Primary focus

Question 12

B cells rapidly dividing every 6 hours to form centroblasts and germinal centers driven by IL-6, IL-15, 8D6 and BAFF are typical of what stage of B cell differentiation into plasma cells?

Answer 12

Secondary focus

Question 13

Which cells make up germinal center dark zones, are the source of proliferating B cells, do not express surface immunoglobulin, undergo somatic hypermutation and class switching?

Answer 13

Centroblasts

*Also Create centrocytes

Question 14

Which cells form the light zone, divide slowly, express surface immunoglobulin, cannot class switch or hyper mutate, interact with and are selected by follicular dendritic cells and are programmed to die?

Answer 14

Centrocytes

Question 15

What are the 3 zones of a germinal center?

Answer 15

1-Dark zone (centroblasts)
2-Light zone (centrocytes)
3-Mantle zone

*T cell area is near by

Question 16

FDC binding to high affinity centrocytes leads to what?

Answer 16

-Tfh cell recruitment which sends the survival signal and causes centricity differentiation

Question 17

Which cytokine leads to centrocyte differentiation into plasma cells?

Answer 17

IL-10

Question 18

Which cytokine leads to centrocyte differentiation into memory B cells?

Answer 18

IL-4

Question 19

What are the 4 broad effector functions of antibodies?

Answer 19

1-Virus and toxin neutralization
2-Opsonization (phagocytosis)
3-Complement fixation and formation of MAC complex
4-Antibody-dependent cell-mediated cytotoxicity

Question 20

Which three Antibody isotypes serve to protect internal tissues?

Answer 20

IgM, IgG, IgA

Question 21

Which antibody isotype is found on mucosal surfaces mainly?

Answer 21

IgA

Question 22

Which antibody isotype aids in parasite immunity?

Answer 22

IgE

Question 23

FcyRI is an example of a high affinity receptor for IgG1 and IgG3 and facilitates signaling, transport, internalization and is found as a monomer or dimer. It is also part of what broader group that facilitate antibody functions?

Answer 23

Fc Receptors

*bind Fc region of the antibody

Question 24

What are three take home points about Fc receptors?

Answer 24

1-Can stimulate as well as activate
2-Are expressed on most leukocytes
3- Form only for IgG, IgE and IgA

Question 25

IgG is transported from the _______ to the _______ which is facilitated by ________

Answer 25

blood stream, tissue, Fc receptors

Question 26

PIgR is a receptor that facilitates what?

Answer 26

Transcytosis of IgA to protect mucosal surfaces

Question 27

Agglutinized antigens are cleared by what?

Answer 27

Erythrocytes binding them via CR1. They are carried to liver or spleen to be taken up by macrophage

Question 28

Which antibody makes mast cells, basophils and eosinophils competent?

Answer 28

IgE

Question 29

Which two antibodies initiate the complement classical pathway?

Answer 29

IgM and IgG

Question 30

_______ is passed during gestation for passive immunity and ______ is passed during breast feeding to protect infant mucosal surfaces

Answer 30

IgG, IgA

Question 31

Activation of B Cells drives what 3 things?

Answer 31

clonal expansion
class switching
somatic hypermutation