The major histocompatibility complex (MHC) plays a central role in the adaptive immune responses. It is a multigene family, that among others, encode for the MHC class I and II cell-surface receptors. MHC class I receptors present peptides from intracellular origin to CD8+ T cells, which may, in the case that the peptide is derived from a pathogen, result in the lysis of the infected cell. The peptide-binding groove of class I molecules is encoded by the alpha 1 and 2 domains, and due to polymorphism has a unique structure. The B and F pockets are generally responsible for binding the anchor residues of a peptide. Based on the functional characteristics and sequence information, the human MHC class I allotypes, HLA-A and -B, have been classified into supertypes.
We, and two other research groups, have investigated the MHC class I variation in bonobos, which resulted in the observation that, compared to humans, this species has an even more diminished MHC-B repertoire than chimpanzees. This is in concordance that in the past, chimpanzee species experienced a selective sweep, probably caused by a SIV-like virus, that targeted their MHC class I repertoire. However, it also suggests that bonobos most likely experienced an additional sweep.
Subsequently, we have investigated to what extent chimpanzee and bonobo MHC class I allotypes can be classified into the human MHC class I supertypes, based on sequence similarity and available peptide-binding-related information for chimpanzee allotypes. Bonobos seem to have maintained two important functional groups of MHC-B allotypes. One having properties similar to HLA-B*27, in humans associated with control of HIV-1 replication. The other MHC-B group was found to show high functional similarity to HLA-B53/B78, which confine the candidate alleles that confer protection from malaria in humans.