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Humans owe important disease-fighting genes to trysts with cavemen

Researchers have unearthed fascinating details about the human species' genetic history since the publication of the genomes of Neanderthals and Denisovans. For example, recent findings show that most humans share up to 4 percent of their genes with Neanderthals.

Now researchers at Stanford have uncovered another interesting insight: some of us owe part of our immune-system function to our evolutionary cousins, according to an article published online today in Science Express.

The article focuses on the efforts of Stanford immunologist Peter Parham, PhD, and colleagues to understand how prehistoric hookups with Neanderthals and Denisovans introduced new variants of immune system genes called the HLA class 1 genes, which are critical or our body's ability to fight pathogens, to the gene pool of modern man. Researchers were specifically interested in discerning which archaic humans were the source of the HLA-B*73 gene type, a genetic variant that is rare in present-day African populations but occurs with significant frequency in West Asian populations.

According to a Stanford release:

By comparing the HLA genes of the archaic humans with modern humans, the researchers were able to show that the HLA-B*73 allele likely came from cross breeding with Denisovans. Little is known about what the Denisovans looked like (the finger bone and the tooth are the only known fossils), but the genome sequence extracted from the finger bone gives insight into where they overlapped with modern humans. Gene flow from the Denisovans into modern humans has left the highest frequency of the HLA-B*73 allele in populations in West Asia, the most likely site for the fortuitous mating to have taken place.

Even in West Asian populations, the HLA-B*73 variant never represents more than 5 percent of all known variants of that gene. However, other human HLA types that arose from ancient matings are found in much greater frequencies ... For example, another HLA gene type, called HLA-A*11, is absent from African populations, but represents up to 64 percent of variants in East Asia and Oceania, with the greatest frequency in people from Papua New Guinea. "The likely interpretation was that these HLA class variants provided an advantage to modern human and so rose to high frequencies," Parham said.

A similar scenario is seen in some HLA gene types found in the Neanderthal genome, which was also sequenced from DNA extracted from ancient bones. These gene variants are common in European and Asian populations but rare in African populations ... Within one class of HLA gene, the researchers estimate that Europeans owe half of their variants to interbreeding with Neanderthals and Denisovans, Asians owe up to 80 percent and Papua New Guineans, up to 95 percent.

Previously: Hey guys, sometimes less really is more, Roots of disease may vary with ancestry, according to Stanford geneticist, Humans share history - and a fair amount of genetic material - with Neanderthals and Open-source encyclopedia of human genome's functional elements in the works
Photo courtesy National Institutes of Health

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