molecules (MHC Class I and MHC Class II) with different tissue dis$

Dr M.R. Clark mrc7 at
Thu Oct 6 05:02:48 EST 1994

In article <4OCT94.08384871 at>,
 <w95_cook at> wrote:
>In a previous article, mrc7 at (Dr M.R. Clark) wrote:

[lots deleted]
>>Well an obvious reason not to have one type of MHC which presents both 
>>endogenous and exogenous antigens is that the T-cell recognising the 
>>MHC+peptide wouldn't be able to tell whether the antigen was exogenous or
>>Or am I missing something in your question? :-)
>>    _        
>I think you're on the wrong track here.  T cells don't discriminate peptides
>as being endogenous or exogenous.  They discriminate self from non-self, but
>even that is maintained through tolerance induction and does not strictly
>depend on which MHC molecule is involved in binding.
[rest deleted]
>Jim Cook
Yes I agree with your message that there is a primary role to allow for 
different profiles of response and the possibility of help and cooperation
between primed and unprimed T-cells.
I guess my reply to the earlier messages was very brief and that is always
dangerous when discussing complex issues. However although it is
semantically incorrect to imply that T-cells "know" the difference what
I was trying to point out was that the system as a whole allows for peptides
to be processed and presented in two different ways (and for the antigens)
to be aquired in two different ways.
These antigens are then presented to T-cells which represent 
different selected sub-populations of lymphocytes which as the rest of 
your message points out interact with each other in a complex way.
But the point is if there were only one type of MHC molecule it would be
very difficult to set up such a complex system

  o/ \\    //            ||  ,_ o   Mike Clark, mrc7 at
 <\__,\\  //   __o       || /  /\,  Cambridge University, Dept. Pathology
  ">    ||   _`\<,_    //  \\ \> |  "to pay for my hobbies I have to work
   `    ||  (_)/ (_)  //    \\ \_    as an antibody engineer"

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