Chapter 7 a) B cell activation

Question 1

Describe the cycle of B cells

Answer 1

B cells grow in BM and thymus

they mature and are activated by secondary lymphoid organs like LN and spleen before entering circulation and traveling to site of infection

Question 2

how are B cells diverse?

Answer 2

combinatorial diversity
- v x j or v xd xj

junctional diversity
-flexible joining at RSS sequences
- P and N nucleotide addition

the combinatorial pairing of heavy and light chains

Question 3

how do we ensure that only one Ab per B cell is expressed?

Answer 3

productive rearrangement and allelic exclusions

2 chnaces for heavy cahin
4 chances for light chain

Question 4

B cell deveopment when we are in periphery and antigen dependent

Answer 4

naive B ceel - mature b cell - then exposed to an antigen whihc it consumes inorder to produce antibodies

Question 5

when travling to LN and spleen describe the antigen

Answer 5

soluble antigen

Question 6

travel to Ln or spine via what?

Answer 6

subcapsular sinus macrophages (SCSM)

Question 7

where in the LN or spleen are Ag transferred to?

Answer 7

follicular DC

Question 8

how are B cells activated from the APC

Answer 8

B cells can be activated via antigen-presenting cell or soluble antigen (tho this is unlikely)

when activated by APC extracts antigen from it so B cell comsumes it through the help of actin, myosin and clathrin

Question 9

what is the APC for B cells?

Answer 9

Follicular DC

Question 10

how does B cell recognition of cell-bound Ag reuslt in membrane spreading?

Answer 10

interactions induce a cluster of BCRS and their cognate antigens

the B cells rapidly spread over the traget membrane before contracting back

Question 11

explain the B cell and APC immunologic synapse

Answer 11

the central supramolecule activation cluster (cSMAC) is surrounded by the peripherial surpamolcule activation cluster (pSMAC) and the distal supramolceule activation cluster (dSMAC)
cSMAC - signaling
pSMAC - integration molecules
dSMAC - like a fence

Question 12

explai the cytoplasmic protion of B cells

Answer 12

other moleculess associet with them for signal transduction

the Ig alpha and Ig beta units whihc have the ITAMs

Question 13

what is the fucntion of ITAMs

Answer 13

immunoreceptor tyrosine actiavtion motif (ITAMs) have Ig alpha/beta phosphorylated on them

phospho-Tyr serve as docking points for adapter molcules

Question 14

B cell activation when tyrosine phosphorlaytion occurs many things happening in the signaling cascade explain them

Answer 14

early steps (0-30mins)

intermediate steps (30 min - 48 hr)

last steps (>48 hrs)

what happens is Btk is produced so that there can be an increase in calcium production

end goal is : generation of many genetically identical effector B cells

Question 15

what do B cells need help from to be actiavted?

Answer 15

help from CD4+ T helper cells

Question 16

how do t-dependent responses require help from T-cells

Answer 16

typically generation upon recognition of proetin Ag

Question 17

in a T-dependent B cell reponse where do animals have to recieve grafts from inorder to produce antibodies??

Answer 17

the thymus and BM

because we need Tcell and B cells

Question 18

describe the steps of a T-dependent B -cell response

Answer 18

1. B cell binds Ag via BCR and this induces intial activation and proliferation events
2. interation with helper T cells provides condition for differntiaition and memory cell proudtcion

Question 19

describe the steps of a T-dependent B -cell response with relation to two signals produced

Answer 19

1. recognition of Ag by multiple Ab cross-linking of Abs is the first signal
   - upregulation of MHC II and B7
   -endocytosis of Ag, presentation on MHC 11
2. MHC II binds peptide on TCR
   B7 : CD28
   upregulation od CD40L
3. recognition of CD40 by CD40L is 2nd signal
   -co-actiavtion of T cell causes T-cell to release cytokines

Question 20

B cell epitopes

Answer 20

B cells bind Ag via Abs, recognixe and bind free antigen in slution

epitopes can be liner or confrontational, must be accessible and on external surface of antigen

Question 21

what is an epitope?

Answer 21

specific protion of an antigen that binds to BCR or TCR

Question 22

what is linked recognition

Answer 22

both the T help cell and B ceel can recognixe the same or different epitopes from the same protein and bind to them

Question 23

what provides the first signal to B cells, what provides the second signal?

Answer 23

1 - Ag
2 - CD40 L

Question 24

where does B cell activation in the LN occur?

Answer 24

the GC

Question 25

what are the parts of the GC

Answer 25

the light zone - FDC and ag-specific B cells

the dark zone - Ag specfic B cells