Interaction among B cell, T cell, & macrophage

R M Bernstein ralph at
Tue Sep 5 13:20:11 EST 1995

In Article <v01510100ac7230de035f@[]>, kdelgert at (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.
>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

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