Chimpanzees may have survived a simian version of the AIDS epidemic 2 million years ago, evolving a defense against the virus that today protects them--but not other primates--from AIDS, say scientists from the University of California, San Diego, and the Biomedical Primate Research Center in the Netherlands. Chimps were found to have only half as many variations in their MHC I immune system genes as humans, a surprise to researchers since the animals typically have about five times as much variation in their genes as people. The fewer variations suggest that an AIDS-like epidemic once hit the animals and over time killed all but those chimps who had the MHC I variations, which protected them against the pathogen. Those genes today continue to provide protection against SIV, the simian version of HIV, the researchers theorize.
The scientists are now expanding their studies to include chimps in the wild to determine if noncaptive animals carry the limited MHC I genetic variations; the scientists are also beginning to look for human versions of the chimp gene variants, which could serve as the foundation for an AIDS vaccine that prompts immune system responses to invading virus.