In article <94198.164503FORSDYKE at QUCDN.QueensU.CA> <FORSDYKE at QUCDN.QueensU.CA> writes:
>> Does an antigen-presenting cell take in antigens randomly? Surely, an
>antigen has first to be labelled as "foreign" by reacting with an antibody
>(either free or cell-bound)? The pre-existing repertoire of antibodies
>then determines which antigens will be taken up. The antibody repertoire is not
>random, so why should antigen-uptake be random?
> Sincerely, Don Forsdyke
Apologies is this a rerun, trn ate my earlier response.
In vitro evidence strongly supports the random uptake of Ag. In an earlier
post on this thread, Ken Frauwirth mentioned a B cell lymphoma LK35.2 that
presented OVA and HEL. For this not to be by random uptake, one would have
to argue that LK35.2 has dual specificities for both Ag, or that it is not
a clone. Both these notions are testable, although unnecessary. Several
groups have used fibroblasts as APC. These cells should not have specific
Ab now, should they? Paul Allen's experiments using hemoglobin as an Ag
have shown that APC pulled right out of the mice express Hb-MHC complexes,
while the mice are completely of that Hb allele. This again argues for
random internalization.
Certainly receptor-mediated uptake is up to 10^4-fold more efficient, but
I think that it's hard to argue that it is the only mechanism of uptake.
Shiv
--
Shiv A. Prasad shiv at lenti.med.umn.edu
Department of Microbiology Lab: (612) 626-0773
University of Minnesota FAX: (612) 626-0781
Box 196 UMHC
Minneapolis, MN 55455
