The major histocompatibility complex (MHC) plays a key role in the immune responses of all contemporary living vertebrate species; it is studied most thoroughly in humans, and is of interest to various researchers active in different fields of science. From an evolutionary perspective, humans and chimpanzees are each other’s closest living relatives. Next to humans, chimpanzees are susceptible to infections with human immunodeficiency virus type 1 (HIV-1), various hepatitis viruses, and Plasmodium falciparum, and are therefore considered to be an important resource for biomedical research. Studies in the twentieth century’s mid-1990s hinted that in comparison to humans, chimpanzees may have a reduced repertoire at one of the classical MHC class I loci. However, a thorough population study on chimpanzees was lacking. Together with the knowledge that chimpanzees can be infected with HIV-1 but do not develop acquired immunodeficiency syndrome (AIDS), the aforementioned observations led to genetic and cellular studies on the pedigreed West African chimpanzee colony housed at the Biomedical Primate Research Centre (BPRC) to sort out the nature of this natural resistance. ...