Something unknowable in immunology? Simple logic?

Dr. Colin R.A. Hewitt crah1 at leicester.ac.uk
Fri Jan 21 10:36:55 EST 1994

Date:          20 Jan 1994 22:52:02 GMT
From:          dfonseca at mail.sas.upenn.edu (Dina Fonseca)
Reply-to:      dfonseca at mail.sas.upenn.edu (Dina Fonseca)
To:            "bionet.immunology mail newsgroup" <bionet-news at daresbury.ac.uk>
Subject:       Re: Something unknowable in immunology? Simple logic?

I recently posted:

I can see that the rate of antigen experience by T cells is 
greatest when younger, but this ignores the fact that new TcR and Ig
are generated right up until the day you die.  Since antigen receptor
 generation is essentially a random process it is inevitable
that cells with self-reactive receptors will emerge from the bone marrow
 all throughout life. If the thymus involutes after
puberty, where are all these new cells getting their education
 (both in +ve and -ve selection)?

and a reply was

>Is this really a problem? If the thymus involutes, then 
>no T cells will be made i.e. no positive selection.
>As no T cells are made, it does'nt matter that there
>is no negative selection either.

But T cells only mature or die in the thymus, they are made in the bone marrow. 
Furthermore, since the vast majority of thymocytes die in the thymus, if the thymus,  
or another organ did not do the job of sorting useful from useless and harmful, we 
would all be full of lymphocytes with no useful function at all. Since this doesn't 
happen, I guess, as have others  in their replies, that some other tissue acts a a 
surrogate thymus when we are adult.

This raises another question I have wondered about........in the normal, uninfected 
individual, how does the immune system know when it is full? i.e. how does it know it 
has enough cells to be effective.

Dr. Colin R.A. Hewitt
University of Leicester/MRC
Centre for Mechanisms of Human Toxicity
Hodgkin Building
PO Box 138
Lancaster Rd

Phone +44 (0)533 525587
Fax +44 (0)533 525616
E-Mail crah1 at le.ac.uk.

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