61-Mature B Cell Responses

Question 1

basic signals required for b cell activation

Answer 1

recognition and binding of Ag
BCR clustering
signal 
1-BCR signaling cascade, activation
signal 
2-co stimulation, survival
signal 
3-cytokine stimuli, expansion and differentiation

Question 2

BCR structure

Answer 2

BCR-Ag binding site, transmembrane, no signaling ability

Question 3

CD79 a/b

Answer 3

adapter molecules

connect surface Ig to intracellular signaling pathway

Question 4

ITAM

Answer 4

tyrosine target that gets phosphorylated to attract signal transduction

Question 5

CD19, CD21, CD81

Answer 5

coreceptor molecules, amplify CD79a/b

Question 6

binding and clustering

Answer 6

Ag binds to BCR, BCR clusters which leads to activation of signal transduction cascade initiated by tyrosine motifs

Question 7

TI Ags

Answer 7

display epitopes recognized by BCR
composed of lipid or carb
activate innate immunity (pattern recognition receptors, complement)
activate B cells

Question 8

TD Ags

Answer 8

display epitopes recognized by BCR
composed of protein
DO NOT activate innate immunity
requires CD4 T helper to provide signals 2 and 3

Question 9

Activation of B cells by TI

Answer 9

signal 1- binding, clustering, signal transduction
signal 2- costimulation from innate signals (TLR, PAMPs, complement)
signal 3- cytokines for expansion and differentiation from innate or T cells (DC, macrophages, neutrophils, NK cells)

Question 10

Marginal zone B cells

Answer 10

TI antigens
epitopes are lipid or carb
rapid BCR and TLR response
does not use CD4 T helper cells

Question 11

Key features of TI B cell response

Answer 11

rapid- do not need CD4T help
Major Ab is IgM
no germinal center-plasma cells short lived, no memory b cells, TI Ab response low affinity

Question 12

Activation of B cells by T cell after infection

Answer 12

signal 1-peptides presented in MHC class II
signal 2- follicular helper cells express CD 154 which bind CD40
signal 3- cytokines to direct CD4 to expansion and differentiation
**use t follicular helper cells for B cell

Question 13

T follicular helper cell

Answer 13

ability to enter B cell follicles and provide signals 2 and 3 to b cells

Question 14

CD 154

Answer 14

expressed by activated T helper cells, ligand for CD 40

Question 15

function of dendritic cells in B cell activation

Answer 15

bring Ag into B cell follicles
epitopes recognized by B cells
Ags bound by BCR-signal cascade initiated by crosslinking and CD79
Ag processed and presented in MHC

Question 16

CD40

Answer 16

constitutive expression on surface of B cells

Question 17

movement of T and B cells to border

Answer 17

after activation the cells coexpress CCR7 and CXCR5 to force movement to border

Question 18

differentiation at T cell zone

Answer 18

1 subset quickly differentiates into antibody secreting cells (plasma cells), short lived, quick response
1 subset migrates back to follicle to seed germinal center response (lose CCR7 and keep CXCR5)

Question 19

cognate interaction

Answer 19

cell driven activation of B cells

Question 20

Germinal center

Answer 20

proliferation and differentiation of activated Ag specific B cells

Question 21

cells in germinal center

Answer 21

Ag specific B cells activated by T follicular helper cells
cells that have lost CCR7 and kept CXCR5
follicular dendritic cells
macrophages to digest apoptotic B cells

Question 22

processes in germinal center

Answer 22

proliferation-mitotic expansion
isotype switching- change heavy chain, requires continued signals 2 and 3
affinity maturation- BCR for Ag becomes higher affinity, requires signals 2 and 3
terminal differentiation- plasma or memory cells

Question 23

isotype switching

Answer 23

in germinal center, change heavy region
selected switch regions brought into close proximity forming a loops
DNA excised and discarded
broken strands ligated
VDJ now proximal to new constant region

Question 24

somatic hypermutaion

Answer 24

B cells given signals by T follicular helper cells to start mutation process
nucleic acid interchanges, mutations can be progressive and accumulate
lead to altered amino acid sequence at Ag binding site

Question 25

affinity selection

Answer 25

limited amounts of original Ag
B cells must compete for this Ag to survive
grab with BCR, ingest, process, and present peptides to provide survival signals
without this they die
mutations with higher affinity=advantage and become plasma or memory cells

Question 26

terminal differentiation

Answer 26

plasma cells or memory B cells

Question 27

plasma cells

Answer 27

secrete antibodies

initially found in lymphoid organs, then move to bone marrow where they survive for years

Question 28

memory b cells

Answer 28

isotype switched
high affinity
long lived
recirculate through SLO
facilitate secondary response when same Ag enters

Question 29

secondary response

Answer 29

same Ag enters, quicker activation with T helper cells, produce high affinity Abs, destroy pathogens before infection

Question 30

vaccination

Answer 30

TD antigens induce B cell activation
germinal center reactions
high affinity, switched Abs
plasma cells
memory b cells