Poor little devils

So, now that I've gotten my 3rd and final Pathology 750 assignment grade back, I'm going to post the first one, which I'm proud of now but at the time was making me sleepless for a week. Since it was my first big assignment after not having had any science classes for 2 years, I was sick with worry after submitting it.

When I logged on to my uni's course content system and saw the 50/50 grade, it was a nearly orgasmic moment: I screamed. ^_^

Performing well academically makes me paranoid, though: it can't be that I'm that smart, I must be screwing up and picking all the easy classes. Low self esteem konon >D

Anyway, a quick run-down of the problem: Tasmanian devils get a peculiar cancer called Devil Facial Tumour Disease, which makes horrendous growths that swell, rot, and eventually cause them to starve to death. Theory is that the etiologic agent (i.e. thingy that causes the disease) is the tumour itself - since devils fight pretty much whenever they meet each other, chunks of tumour cells break off, stick to the new host, and grow on it.

People think this is possible because devils went through a population bottleneck at some point, so they're very inbred and therefore don't mount an immune response to each other's cells. Contrast this to humans who need to take powerful immune-suppression drugs if they receive organ transplants, even from relatives.

For the question we were asked to come up with an alternate theory (since reduced genetic diversity doesn't automatically translate into an epidemic of transmissible cancer) involving "the failure of the MHC class I antigen processing and presentation machinery". I racked my brains about it for the better part of a week until having an "eureka" moment that it was similar to something else we'd discussed in class - Canine Transmissible Venereal Tumour (great disease name, tells you exactly what it is).

Download a .pdf of the essay here.

I was really afraid that my answer was too "off" to be acceptable, but surprisingly the prof liked it. Anyway, I'm sort of proud of my answer because at the time I wrote it there wasn't any information out there to really confirm the popular model.

Although it turns out that someone's gotten around to testing devils' immune reactions against each other (scroll down to "A Contagious Cancer") and they really don't recognize other devils' cells as foreign.

Mixed lymphocyte reactions were then undertaken to investigate whether the Tasmanian devil has the correct genes to allow recognition of foreign cells. This was performed by mixing lymphocytes from many devils to see if they reacted to each other. The results from these studies clearly showed that devils failed to recognise cells from other devils as different. This provides strong evidence that a lack of genetic diversity contributes to why the cancer is infectious.

There goes my pretty theory. The scriptwriter for Stargate SG-1 who had a character say "I'm a scientist. It's just as exciting for my theories to be proved wrong as to be proved right," clearly hasn't talked to any of us recently...

Too bad the prof didn't comment on my really really alternative theory of DFTD etiology (or aetiology if you're British): Martian cancer rays!