B cell differentiation
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rearrangement of D-J of heavy chain
rearrangement of V-DJ of heavy chain
large Pre-B cell
small amts of expression of heavy chain on outside of receptor; expression signals termination of heavy chain gene rearrangement
Surrogate L chain
made of VpreB and lambda 5 proteins; act as "L" chain so heavy chain can be expressed on outside of B cell in Pre-B cell stage
its presence signals to stop H rearrangement and start L rearrangement
mu Heavy chain
its expression stimulates L chain rearrangement
L chain rearrangement inhibitor
causes VpreB and lambda 5 to be displaced and allows L and H chain to come together
How does RAG play a role in B cell dev?
it can phosphorylate to cause cessation of H chain gene rearrangement in pre-B cell stage
turned on for L chain rearrangement
When do L chains stop rearranging?
one IgM is expressed on the surface of immature B cells
What are three fates of immature B cells in bone marrow?
- 1. strong signal binding with self-antigen=clonal deletion and apoptosis
- 2. signal binding w/ sol self-antigen=immature B cell migrates to periphery and becomes inactive to Ag and eventually dies
- 3. no signal binding w/ self-antigen=migrates to periphery and becomes mature B cell (expresses IgD and IgM)
transitional B cells
- immature B cells that leave bone marrow and enter periphery; can mature into 3 types of B cells:
- 1. B-1 B cells
- 2. marginal zone B cells
- 3. follicular B cells
B-1 B cells
forms from transitional B cells; resides in pleural and peritoneal cavities and make natural Ab to function in innate immune response; esp useful against bacteria
Marginal zone B cells
live in marginal zone of spleen and make T-indep and T-dep Ab responses to bloodborne Ag
Follicular B cells
recirculate btw blood and lymphoid follicles and make T-cell dep and participate in germinal center rxn
What are some characteristics of plasma cells?
- no surface Ig
- no MHC-2 expression
- make secreted form of Ig
- are not inducible (growth)
- end stage of B cell differentiation
What are some characteristics of a resting B cell?
- isotype switch
- expresses surface Ig
- expresses surface MHC-2
- does not secrete Ig
- is inducible (growth)
What are some characteristics of memory B cells?
- can revert back to resting B cell stage
- can express any Ig class
- go to live in bone marrow and can stay for yrs
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