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The C region in the human heavy chain DNA (after the VDJ rearrangement) is VDJ---Cm--Cd--Cg--Ce--Ca
If a Bcell is instructed to switch from IgM to IgE, then the DNA for Cg is lost (because its inside the cutting loop).
My question is: A Bcell gets instructed to switch from IgM to IgG. Can it be again instructed to switch to IgE and then to IgA, since the Ce and Ca are downstream? Does a Bcell secreting IgG have the genes for Ce and Ca? On another instance the books say that once a Bcell is activated, then it can either die or convert to memory cell. I'm getting a bit confused here! Can anyone help?
Edited by usmlegr on Nov 01, 2005 - 10:03 AM
i looked this up in warren levinson..Once a Bcell has class switched past a certain H(heavy)-chain gene, it can no longer make that class of H chain because the intervening DNA is excised and discarded.
in conclusion if the class switching has occurred from M to G it can switch, if the need arises, to A and/or E in that order. [M,G,A,E] however, you must bear in mind that the antigenic specificity remains the same once the antibodies have started to be produced.
maybe someone with more knowledge on this can explain better...Good luck
after the vdj regions there re the mu and the delta region, and when the ab is made it can be made with the same specificity as either igd or igm at first, so anyone can be formed at the first instance , though we mostly get igm, after that the switching can occur to igg and then iga etc
so, the rules re the class switching always occurs downstream and requires t cells for it
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