In article <2hn1ui$m72 at netnews.upenn.edu> dfonseca at mail.sas.upenn.edu (Dina Fonseca) writes:
>>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)?
>>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.
The underscored statements seem contradictory. Experiments with adult thymec-
tomized mice, adult bone marrow chimeras, and sublethal radiation of adult
mice suggest that involution of the thymus does not render it non-functional.
Shiv A. Prasad shiv at lenti.med.umn.edu
Dept. of Microbiology pras0005 at student.tc.umn.edu
Univ. of Minnesota