MHC restriction questions

Klaus D. Elgert kdelgert at
Tue Oct 20 13:22:40 EST 1998

Immunology, particularly MHC restriction, aficionados:

While we were discussing MHC restriction in class, an interesting group
of student questions were posed.  Something along the following lines:=20
"Somatic mutation does not occur in the TCR because it would be
detrimental to generate self-specific T-cells.  Yet, we display
self-peptides in our MHC molecules.  Why haven't we developed
mechanisms to display only foreign peptides? Also, if somatic mutation
can potentially lead to self-specific T-cells, shouldn't the same hold
with B-cells?"

Beyond the exceptions, I gave the canned answers that random mutation
of the TCR may change thymic-induced specificity leading to
autoreactivity; there are autoreactive B cells but T cells would
control them, polyclonal B-cell activation, etc.  Your comments?

Also, what about the following, why not "=8Adisplay only foreign
peptides?"  Teleological reasons could be given, possibility for
chronic activation, self-peptides used in thymic selection, etc.  I
would be interested to hear other comments.


Klaus D. Elgert

Microbiology & Immunology Section

Biology Dept

Virginia Tech

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