Paper short abstract:

To investigate how and why modern humans have adapted to endemic pathogens, we examined the polymorphism at primate DRB1, which encode a protein playing an important role in pathogen recognition. We found the presence of a human specific allele group that has been maintained in the population before the divergence from chimpanzees.

Paper long abstract:

Modern humans live in a wide variety of environments, from polar to tropical regions. The endemic pathogens in these areas differ, and humans are possible to be infected by these pathogens. Modern humans disseminated across the world from Africa 100,000 to 50,000 years ago and have adapted to regions with various endogenous pathogens. On the other hand, chimpanzees have remained in Africa since their divergence from humans approximately 6 million years ago. This begs a question of how modern humans acquired resistance to a variety of pathogens in different environments. In the present study, we examined phylogenetic relationships among primate alleles of the major histocompatibility complex (MHC) DRB1 gene, which is an important genetic system for protection against infectious disease. The analysis identified two major groups of HLA-DRB1 alleles, Groups A and B, and demonstrated that Group A was a human-specific. Our estimates of divergence time of these alleles suggested that HLA Group A alleles have been maintained in the human population before the divergence of humans and chimpanzees. On the other hand, most orthologs of HLA Group A alleles have been lost in the chimpanzee probably due to changes in selective pressures. Three HLA Group A alleles have likely increased in frequency among human populations after their out-of-Africa event, suggesting that these HLA molecules contribute to the local adaptation of humans.