chapter 11

Question 1

All receptors on a single B cell have what type of specificity for antigen?

Answer 1

identical

Question 2

B cells with receptors for self-antigens are deleted during ____________________________.

Answer 2

embryonic development

Question 3

-response that require help from T cells
-typically generated upon recognition of protein Ag

Answer 3

T-dependent (TD)

Question 4

-responses that do not require T-cell help
-generated upon exposure to multivalent/polymerized Ag

Answer 4

T-independent (TI)

Question 5

bind to B cells through PRRs and mIgs

Answer 5

TI-1 Ag

Question 6

cross-link large numbers of BCRs

Answer 6

TI-2 Ag

Question 7

Describe the basics of the clonal selection hypothesis:

Answer 7

-each B cell bears a single type of Ig receptor
-on stimulation, each cell will create a clone of cells bearing the same antigen receptor as the original

Question 8

Proliferation induces formation of _________________________in lymph nodes/spleen.

Answer 8

germinal centers

Question 9

What provides conditions for differentiation and memory cell production?

Answer 9

interaction with helper T cells

Question 10

Naive B cells circulating in the periphery pass through the ___________and _____________regularly, where they meet antigen

Answer 10

lymph nodes and spleen

Question 11

Antigen recognition by mature B cells provides a _____________________

Answer 11

survival signal

Question 12

B-cell recognition of cell-bound antigen results in _____________________.

Answer 12

membrane spreading
-Next, the B cell rapidly spreads over the target
membrane before contracting back

Question 13

What causes clustering of B-cell receptors upon Ag binding?

Answer 13

-Ag binding induces conformational change in Cμ4 domain
* This causes oligomerization of Ag-bound IgM molecules in the `plane of the membrane
* The molecules move into lipid rafts of the membrane

Question 14

Describe internalization induced by antigen receptor clustering:

Answer 14

– Once signaling begins, BCR-Ag complexes are internalized
– Internalized Ag are processed in the exogenous pathway
– Ag peptide fragments are presented in MHC class II molecules on the B-cell surface to solicit T-cell help

Question 15

What happens after B cells engage their cognate T cell partners?

Answer 15

B cells then downregulate CCR7, leave T cell areas, and eventually enter follicles

Question 16

Some activated B cells migrate into borders of T cell areas and form primary foci and differentiate into ___________________.

Answer 16

plamsablasts (plasma cells)

Question 17

What happens when activated B cells move into B cell follicles?

Answer 17

-they begin to express Bcl-6 transcription factor
-they continue to differentiate with help of TFH cells

Question 18

Where do plasma cells from?

Answer 18

within the primary focus

Question 19

Ig producing machines

Answer 19

plasma cells

Question 20

When are plasma cells found?

Answer 20

within the first 5-6 days of immune responses

Question 21

differentiated B cells that have began to secrete antibodies, have not yet lost the capacity to proliferate, and still bear cell surface BCRS

Answer 21

plasmablasts

Question 22

differentiated B cells that can no longer divide, bear little to no cell surface immunoglobin, and rapidly secrete large numbers of antibody molecules

Answer 22

plasma cells

Question 23

What is required for germinal center formation?

Answer 23

CD40/CD40L interactions between B/T cells
-cytokines from FDCs and TFH cells stimulate proliferation further

Question 24

describe the dark zone

Answer 24

densely packed with proliferating B cells

Question 25

describe the light zone

Answer 25

B cells interspersed with a network of FDCs

Question 26

What two extraordinary processes occur within the germinal center?

Answer 26

somatic hypermutation/affinity selection and Ig class switch recombination

Question 27

What is somatic hypermutation (SHM)?

Answer 27

it produces individual point mutations in Ig variable (but not constant) regions
-followed by affinity selection

Question 28

What is affinity maturation?

Answer 28

the increase in average antibody affinity for an antigen that occurs during the course of an immune response or in subsequent exposure to the same antigen

Question 29

What is class switch recombination?

Answer 29

the generation of antibody genes for heavy chain isotype other than μ and δ by DNA recombination

Question 30

produces opportunity for mutation by altering deoxycytidine bases

Answer 30

activation-induced cytidine deaminase (AID)

Question 31

Recombination occurs between donor and acceptor ________________________.

Answer 31

switch (S) regions

Question 32

What are switch regions?

Answer 32

-tandem repeats of short, G-rich sequences 20-80 bp long
-contain targeting sites for AID

Question 33

What signals are needed for class switch recombination?

Answer 33

-B cells must receive costimulatory signals from CD40/CD40L to engage in CSR
-Cytokine signal determines Ig isotype

Question 34

Nude mice have the Foxn1 mutation that results in athymia. They can still respond to what type of antigen with antibodies?

Answer 34

T-independent

Question 35

typically bacterial cell-wall components, bind to innate immunity PRRs on B cells

Answer 35

TI-1 antigen

Question 36

polymeric protein Ag and capsular polysaccharides, crosslink many mIgM BCRs

Answer 36

TI-2 antigen

Question 37

What are the two novel subclasses of B cells that mediate the response to T-independent Ag?

Answer 37

B-1 B cells
Marginal zone B cells

Question 38

Negative signaling through ____________________shuts down unnecessary BCR signaling.

Answer 38

CD22

Question 39

Negative signaling through _________________ receptor inhibits B-cell
activation.

Answer 39

FcγRIIb
-Circulating IgG can bind this receptor and shut down B-cell
activation

Question 40

How do B-10 B cells act as negative regulators?

Answer 40

They secrete IL-10 which shuts down inflammatory responses by T cells and APCs