In article <ralph.1153450892A at 128.196.137.12>,
Ralph M Bernstein <ralph at ccit.arizona.edu> wrote:
[snip]
>> yes upon thymic epithelium, but supposedly against self antigens. the
>tecs as well as the macrophages in the cortex may perform differential
>presentation , perhaps presenting the same peptides in different ways from
>all antigens in the thymus. and since bcells can be in the thymus, their
>antigen receptors may be presented and selected against.
> __but_ the point actually is that tcells are mhc restricted, right?
>right. and dr fuchs point is that idiotypes can stim a response. and since
>only peptides, not idiotypes can be presented -thru mhc restriction- these
>antigens (the recombining sites) are really irrelevant.
Ralph,
I think you are being a little pedantic about this point. I understand
what Dr. Fuchs is saying but you are pretending not to I think.
The fact is that Ig molecules can be processed and presented on MHC
like any other protein. Sometimes the peptides will be presented on
B-cells in the context of Class II. Some of these peptides will
be derived from V-regions and some will come from frameworks others
from hypervariable regions. Some will arise as a result of VDJ combinations
and others through somatic hypermutation. Technically they are not the
same as the classical definition of an idiotope or an idiotype but they
may be related to these.
The point is that you can't really learn tolerance in advance to a protein
which somaticaly mutates at a high frequency eg Ig and hence you have to have
a mechanism which allows for the situation of a mature T-cell encountering
antigen for the first time on an activated and hyper mutated B-cell.
I'd love to know the answer to this question and I think that the
"Danger" "No Danger" idea offers some hope of an explanation
Regards,
Mike Clark, mrc7 at cam.ac.ukhttp://www.path.cam.ac.uk/MikeClark/
--
o/ \\ // || ,_ o Dr. M.R. Clark, Division of Immunology
<\__,\\ // __o || / /\, Cambridge University, Dept. Pathology
"> || _`\<,_ // \\ \> | Tennis Court Rd., Cambridge CB2 1QP
` || (_)/ (_) // \\ \_ Tel. 01223 333705 Fax. 01223 333875
