Why will MHC indicate graft as foreign?

Mr. Hat misterhat at sbcglobal.net
Tue Jul 8 20:49:13 EST 2003

In article <noemail-42FD4D.23464007072003 at cnews.newsguy.com>, Hobo
<noemail at noemail.com> wrote:

> I've read that cancer cells downregulate MHC expression, often to zero. 
> NK cells are programmed to kill cells with zero MHC expression. I've 
> read that the cancer cells avoid this by expressing MHC homologs at the 
> surface, fooling the NK cells. If the immune system can be fooled so 
> easily by MHC homologs, why is it so sensitive to differences in MHC 
> composition between native and donated tissue?

Because the whole story in the instance of transplantation is not just a
cut-and-dried thing where a donated tissue expressing MHC phenotype "X" is
placed into the context of recipient tissue expressing MHC phenotype "Y".
A major factor involves donor-derived APCs and/or other donor factors that
are transferred along with the organ or tissue transplanted.


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