When our ancestors mated with Neanderthals and Denisovans, a recently discovered archaic human group, they picked up some of their genes. Now researchers say that DNA inherited from these extinct hominids may have fortified the modern immune system. A team at Stanford University focused on human leukocyte antigen (HLA) class 1 genes, which play a vital role in rallying the immune system to fight off bacteria and viruses. Because diseases can be endemic to specific regions of the world, these genes exist in thousands of versions, known as alleles.
To analyze the origin of these alleles, the scientists looked at bone marrow registries containing the HLA genes of millions of people from all parts of the globe. By comparing DNA from modern populations with the reconstructed genomes of Neanderthals and Denisovans, they discovered that several HLA variants from the archaic groups are still around. For example, the ancient gene for HLA-A, which helps the body resist viruses like Epstein-Barr, is present in half of all modern Europeans, more than 70 percent of Asians, and up to 95 percent of people in Papua New Guinea. Other ancient alleles are involved in the regulation of natural killer cells, essential for immune defense.
Our ancestors’ liaisons with Neanderthals and Denisovans may have made them less susceptible to local infections, proposes Stanford immunologist Laurent Abi-Rached, giving them a survival advantage as they migrated out of Africa to Europe and Asia. “Breeding with our evolutionary cousins may have facilitated the spread of modern humans by preventing them from getting sick.”