Immunity in modern Homo species boosted by genes from archaic humans

During human evolution, there can be neutral mutations (resulting in ‘genetic drift’) and positive-selection mutations (caused by selective pressures).  Human genes governing innate immunity provide a valuable tool for the study of the selective pressure imposed by microorganisms on host genomes. Attached are two articles (the first from France, second from Germany) that are comprehensive, genome-wide studies of how selective constraints and adaptations have driven the evolution of innate immunity genes.

 Among the genes presenting highest Neandertal ancestry, both groups independently studied the Toll-like receptor gene cluster (TLR6-TLR1-TLR10), because modern humans were found to carry three distinct archaic haplotypes.  Two of these haplotypes are most similar to the Neandertal genome, and the third haplotype most similar to the Denisovan genome. TLRs are key components of innate immunity that provides an important first line of immune defense against bacteria, fungi, and parasites. The unusually high allele frequencies and unexpected levels of population differentiation indicate there has been local positive selection on multiple haplotypes at this locus. The introgressed alleles of these TLR genes appear to have clear functional effects in modern humans––associated with increased microbial resistance and increased allergic disease in the large cohorts studies. These studies provide strong evidence that recurrent adaptive introgression at the TLR6-TLR1-TLR10 locus has resulted in differences in disease phenotypes today in modern humans

 Am J Hum Genet  2o16; 98: 5–21  and  ibid, pp 22–33

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