In Article <v01510100ac7230de035f@[128.173.187.15]>, kdelgert at vt.edu (Klaus
D. Elgert) wrote:
>Immunology netters:
>>Along the recent lines of posting questions asked, in this case, by a
>graduate student during an undergraduate immunology lecture on antigens. I
>told her to see me later in the week, so how about some help before she
>gets here. The jest of her two questions was something like this (I
>think). We have a B cell specific for antigen X. It captures antigen X by
>its antibody receptors. These antibody receptors are directed against a
>specific epitope. Question 1: Once the B cell internalizes antigen X, how
>does it display (or know to display) the same epitope (peptide) by its
>class II molecules to the appropriate Th cell TCR?
ahh, good question. answer...i think that it probably does not. the
crosslinking of the ig receptor on the surface activates the b cell
(hopefully it is a memory b cell for best activation, otherwise a whole slew
of "strange and wonderful" things can happen depending upon, a) if a
secondary signal, ie cd 40 ligand is around, or b) if the b cell is
naive-then deletion, anergy, etc) the result in mature memory is what is
known as a determinant spreading. the b cell is specific for determinant
"d", it binds "d", takes in the protein/peptide and it is processed in the
phago/lysosomes, etc. (that b cell at this time proliferates and produces
ig, and the receptor can undergo affinity maturation ) "d" is presumably
bound by a high affinity antibody. the proteosomes digesting the complexes,
etc, for class II presentation, are snipping away at the protein/peptide.
the map of the protein peptide is abcdefg. since "d" is "bound", "c" and
"e" are now what is presented, activating tcr bearing t cells specific for
"c" and "e" therefore enlarging the cascade, which then activates more b
cells in contact in association with the b and t cells in that "area". so
the "determinant" can therefore "spread". for better explanations of this
use medline to look up some of e. sercarz's work.
> Question 2: If it is
>the same epitope, how does this Th cell become primed to the same peptide,
>through macrophage peptide-class II complex presentation, so that it can
>help the appropriate anti-X B cell? (When T cells do not recognize the
>same epitopes that B cells do.) This B cell then undergoes differentiation
>into a plasma cell, secreting antibody that reacts to the capture epitope.
>
hence the secondary signal part of activation. look up cd 40 and its
ligand, b7-1 b7-2 ctla4 and cd 28. i think the b7-1 can be found under
author t.suda, although i could have his name wrong. there are actually
several immunology today reviews which would be great for undergrads.
>Thanks in advance for your responses.
>>Ciao,
>Klaus Elgert
>Dept. Biology
>Microbiology & Immunology Section
>Virginia Tech
>
regards, ralph
Ralph M. Bernstein
Dept of Micro/Immuno
University of Arizona
Ph: 602 626 2585
Fx: 602 626 2100
url: http://lamprey.medmicro.arizona.edu