IMMUNO 11_BCR, BCELL MATURATION

B cell maturation starts in the bone marrow and finishes in the ______

secondary lymph (often the spleen)

what cells of the bone marrow provide growth factors, cytokines and adhesion molecules to delevoping B cells?

mesenchymal stromal cells

stromal cells secrete IL7 and CXCL12 what do those do?

IL7- commits the common lymphoid proginator to the B cell lineage

CXCL12 binds CXCR4 and keeps the B cells in the bone marrow for development

what does Kit-SCF signaling do?

support pre-pro and pro B cell survival

what transcription factors are associated with B cell development?

E2A

F0X01

EBF

PAX5

what two TF in B cell development upregulate Rag 1:2 to start VDJ?

E2A and EBF

what are the stages from the multipotent proginator to the mature B cell? (10 stages)

multipotent porginator

common lymphoid proginator

early pro B

late pro B

large pre B

small pre B

immature B

transitional B 1

transitional B 2

mature B cell

in the stages of B cell development, where does the cell move from the bone marrow to secondary lymph?

transitional (T1/T2)

at which stage of B cell development does antigen dependance start?

at immature B cell when need to test the TCR

what checkpoint is antigen independant? what stage of development?

checkpoint 1 at large pre B

H chain has surrogate L chain and testing of preBCR

even tho antigen isnt needed to test the pre-BCR what signalling molecules are needed?

IgA/IgB (have the ITAMs)

if the pre-TCR is sucessful what phase can the B cell move into?

VJ recombination to make a true L chain in small pre B

what are the three checkpoints of the BCR making process?

checkpoint 1- test preTCR (test B chain)- no antigen

checkpoint 2- test TCR (test a and B chain work together)- antigen in negative selection for central tolerance in the bone marrow

chckpoint 3- test TCR for periphreal tolerance in the spleen (secondary lymph)

there are two types of self tolerance explain each:

periphreal tolerance

central tolerance

periphreal tolerance- B cells get periphreal tolerance due to negative selection in the secondary lymph

central tolerance- T cells and B cells get central tolerance due to negative selection in the primary lymph

why do B cells need to get periphreal tolerance and T cells dont?

B cells dont have AIRE and have to test against self antigens from around the body by negative selection in the secondary lymph

whereas T cells have AIRE and can test against self antigens in the thymus (primary lymph)

what phase does developing B cell express IgM on surface and do negative selection (central tolerance)?

checkpoint 2 in the immature B cell

what phase is IgM and IgG expressed on the B cell and the B cell undergoes periphreal tolerance negative selection?

checkpoint 3 at stage of transitional 2

explain what happens in each major stage

common lymphoid proginator

early pro B

late pro B

large pre B

small pre B

immature B

transitional B 1

transitional B 2

mature B cell

common lymphoid proginator- IL7 commits the cell to B lineage

early pro B- D→J on heavy chain

late pro B- V→DJ on heavy chain

large pre B- checkpoint 1- expression of functional muH chain and surrogate L chain to form pre-BCR test

small pre B- V→J on L chain

immature B- checkpoint 2- expression of IgM

transitional B 1- express IgM, T cells enter folicles of spleen and express BAFF-R

transitional B 2- express CD21 as well

mature B cell- express IgM and IgD

the surrogate L chain is made of two components ____ and ______

VpreB and lambda5 (the symboyl)

in the initial H chain testing in the preBCR what type of H chain is used?

mu H chain

RAG1:2 is expressed in early→late pro B and then isnt during large preB, but then is expresssed again in small preB→immature B, then is no longer expressed.

why is there a lack of RAG1:2 expression in the large preB phase

H chain is being tested and RAG1:2 is not needed again until the light chain is made

is the heavy chain at the phase of preBCR considered Hmu or HM?

Hmu, HM is only once it is a TCR

when is the surrogate L chain no longer expressed

after preBCR testing is done (not expressed past the large preB stage)

when is tDt expressed in BCR stages?

from the early proB to small pre B (while VDJ and VJ recombination are occuring)

how many chances does the BCR heavy chain have to make a successful H chain?

2 chances on each of the 2 chromosomes = 2×2=4 chances

does the chances to recombine H chain occur in early proB (D-J) or does it need chances in late proB (V-DJ)?

D-J occurs easily

uses up 4 chances if needed in V-DJ recombination

if VDJ is sucessful in heavy chain what stage is next?

large preB

what is the default pathway?

apoptosis

the VDJ recombination of only 1 H chain per chromosome is tested in checkpoint 1 (large preB)

this is called ______ exclusion

allelic exclusion

preBCR signaling is antigen (dependant/independant)

independant

in small preB when VJ recombination for L chain is occuring is kapa or lambda chain made first?

kappa

how many attempts does the L chain have at VJ recombination?

4

2 attempts at kappa first

then if kappa fails 2 attempts at lambda before apoptosis

a sucessful light chain pairs with the mu H chain to form

sucessful BCR (IgM (k/ or lamba))

which chains in BCR have allelic exclusion?

which chains have isotypic exclusion?

H and L chains have allelic exclusion

L chain also has isotypic exclusion (k or lambda)

in the first round of negative selection (checkpoint 2) if the BCR cell fails what happens?

the B cell can undergo receptor editing to reactivate RAG1:2 and attempt to make a different L chain that works

which chains can undergo receptor editing?

L chain only

when is B cell allowed to leave the bone marrow?

is it mature now?

after passing checkpoint 2 and central tolerance established

no still needs to pass checkpoint 3 in the periphery

when a BCR is too reactive this is noticed by the strong _____ in response to a self antigen

BCR cross linking

what type of selection occurs in the spleen?

negative selection (checkpoint 3) to establish peripheral tolerance

how do immature/ transitional B cells get to the spleen?

blood stream

negative selection in the spleen is antigen dependant, how are antigens expressed?

by splenocytes and soluble molecules circulating the blood

if a B cell fails checkpoint 1 can it attempt to undergo recombination again?

if a B cell fails checkpoint 2 can it attempt to undergo recombination again?

if a B cell fails checkpoint 3 can it attempt to undergo recombination again?

1- no, the H chain cannot be rearranged if it fails→apoptosis

2- yes, the L chain can be rearranged again until the genes run out→ apoptosis

3- no, once past second checkpoint the L chain does not have ability to rearrange again

if BCR fails checkpoint 3 what happens?

apoptosis or anergy

transitional B cells enter _____ of spleen recieve maturation signals and can become mature B cells

folicles

if a transitional B cell enters the marginal zones of the splenic white pulp (instead of the folicles) what happens?

marginal zone B cells are produced

what does a marginal zone B cell do?

are first responders to blood born antigens and pathogens

what is maturation factor to B cells in the folicles of spleen?

BAFF

what stage of B cells can express BAFF-R and bind BAFF from folicular dentritic cells?

T1 -transitional 1 (and T2)

transitional 1 B cells express:

transitional 2 B cells express:

transitional 1 B cells express: IgM, BAFF-R

transitional 2 B cells express: IgM, IgD, BAFF-R, CD21 complement receptor

T1 B cells that dont recieve BAFF die withing ______ days of leaving bone marrow

2-3 days

immature vs mature B cell expression difference?

immature- IgM

mature- IgM and IgD

what allows for co-expression of IgM and IgD on mature B cells?

alternative splicing of the primary RNA transcript