A devastating illness is sweeping through Tasmanian devil populations, slowly moving westward across Tasmania. It's called Devil Facial Tumor Disease (DFTD), and it's a kind of cancer. The strange part is that the disease is transmitted by transferring tumor cells to uninfected devils through biting. The tumor cells begin growing into tumors and eventually kill the new host. This disease could very well drive the Tasmanian devil to extinction. Poor devils. One would think that the immune system would reject these foreign tumor cells at least in some devils, much like organ transplants of the wrong tissue type are rejected. New research from Siddle et al. sheds light on this possibility.
Siddle et al. looked at Major Histocompatibility Complex (MHC) genes from 53 devils sampled across Tasmania and found two major types of MHC sequences. They also found that devils have a variable number of MHC loci, something also observed in other animals like cows, rats, and pigs. Most devils that they surveyed had both of the major MHC types, as did the DFTD cells. There were, however, a few populations of as yet uninfected devils that had only one type of MHC genes. Siddle et al. speculate that the immune system of these devils might recognize the foreign tumor cells more readily than devils with both MHC types. I hope they're right.
Siddle et al. 2010. MHC gene copy number variation in Tasmanian devils: implications for the spread of a contagious cancer. Proc R Soc B doi: 10.1098/rspb.2009.2362.