hehehe Im not an immunologist. But this paper Ive been wanting to write about for weeks had too many weird things in it for me to ignore.
A unique T cell receptor discovered in marsupials.
Heres the background-- part of your adaptive immune system is made up of T-cells. T-cells have, well, T-cell Receptors in their cell membranes to recognize when something 'non-self' is floating around. For instance, if a cell is infected with Chicken Pox, it will 'present' bits of virus in MHC molecules. A Cytotoxic T-cell comes along, and is like 'WHOA! What the hell are you doing??' and kills the infected cell.
Well, doesnt 'kill' the infected cell. It persuades the infected cell to commit suicide. Weird, but true.
There are billions upon billions of non-self things that might need to be recognized at some point during your life-- How does your adaptive immune system do it?? When youre a baby you create a huge library of potential adaptive immune cells through various genetic recombinations (you dont really have an adaptive immune system until youre 2-ish). For T-cells, any TCR that recognizes something your body makes is killed-- all the other T cells are left alone.
TCRs are usually made of alpha and beta units, or gamma and delta units. Its very well conserved, evolutionarily. Well researchers found a WHOLE NEW set of genes (eight clusters) that code for TCRs in marsupials (American and Australian) they named mu! Its related to the TCR delta genes and Ig heavy chain genes (used in B-cells). Weird!
AND SOME MEMBERS OF THE MU FAMILY DUPLICATED THROUGH RETROTRANSPOSITION!
Which means the recombination steps have already taken place, and there are no introns! It still works, and I dont know how to describe it better than the pic in the paper-- but for those of you without PNAS, the joined VDJ just sort of piggy-backs on another V region. And marsupials use them! These sequences are under positive selection! Its just that one of the possible TCRs has 2 V's. Really weird!
Bleh they needed more pics in this paper though. Im still not sure I totally *get it* Too weird :P Heres UNMs press release that describes the impact of this finding.
Sunday, June 17, 2007