Sunday, June 17, 2007

Weeeeeeird! (immune system evolution news)


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!



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.


Jon said...

I read research like this and I wish I had studied more microbiology (and philosophy) in college. I'm happy I have engineering degree but I have such a yawning gap to even grasp this kind of stuff. I just take it on faith in my own way.

I love your blog. Have you considered getting a webcam and doing a similar vlog form? I vlog on YouTube a lot.

VWXYNot? said...

Is anything known about the kinds of infections that marsupials get? I know they have endogenous retroviruses, but that's the extent of my knowledge. IIRC, cytotoxic T cells also kill off cancerous cells. I wonder how the rates of viral / bacterial infection and cancer look in these species.

VWXYNot? said...

My goodness, I just read the press release. You know when you read something and all you want to do is edit and re-write it? It's not exactly clear...

ERV said...

Jon-- hehehe No, Im funnier in writing. Plus Id have to stop every 2 minutes to yell at Arnie for chewing on something...

vwx-- Further avenues of research!! :P

I think a problem now, though, is that the small-tailed possum is used for some kind of cancer research... what if we arent getting the picture we think we're getting because of these weird TRCs?

Eh I want more data! hehe Which is what those PIs want to hear!

VWXYNot? said...

I knew I'd read something somewhere - it was National Geographic. Tasmanian Devils can be infected by a weird kind of transmittable cancer. It's passed on when they bite each other, injecting malignant cells into the victim (vicious wee beasties). I wonder if this new information about their immune system has any relevance to this disease?

Link at