Price of protection: Immune-gene version, great at combating leprosy, is not without drawbacks

Leprosy begins with a bacterial infection and, after five to 20 symptom-free years, can end in severe nerve, skin, vision and respiratory-tract damage and limb amputations. Treatable and in decline today, this scourge has plagued humanity for many thousands of years and still persists in Southeast Asia and India. […]

Read more of Bruce Goldman’s report on our latest study for Scope

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An immunity gene evolved in Southeast Asia to protect against leprosy

A mutation in an immune system gene rapidly rose in frequency in Southeast Asia approximately 50,000 years ago because it likely conferred protection against leprosy, which spread to the region from Africa around the same time. The findings, published May 16th in Cell Reports, show that the gene variant, called HLA-B*46:01, encodes a protein that binds to molecules derived from the bacterium that causes leprosy–a chronic infection of the skin and peripheral nerves. This HLS protein then presents these foreign molecules to the immune system, which destroys the infected cells.

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NK cell immunity gets schooled

Population-level genetic analysis can give us clues as to which factors guide immune evolution. Now, Horowitz et al. have applied this analysis to polymorphisms in HLA that affect NK cell education. They find that the HLA-B haplotype −21M that delivers functional peptides to the conserved CD94/NKG2A receptor rarely encodes ligands for the more diverse killer cell immunoglobulin-like receptors (KIRs), in contrast to the haplotype −21T, which does not deliver functional peptides. Individuals homo- or heterozygous for −21M are more likely to have more diverse CD94/NKG2A+ NK cells, suggesting that these HLA haplotypes may have specialized to either the KIR or CD94/NKG2A school through complementary coevolution.

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Old and new immune genetic variation

The Khoe-San people of Africa are one of the most ancient lineages of humans and thus can be examined to identify both ancient and recent humanspecific genetic variation. Investigating the alleles of the killer cell immunoglobulin-like receptors and their human leukocyte antigen class I ligands, which are involved in the immune response, Hilton et al. found evidence of both old and new genetic variants. Because these genes can affect pregnancy, the identification of one recently evolved variant at relatively high frequencies suggests that it may have conferred a selective advantage.

PLOS Genet. 10.1371/journal. pgen.1005439 (2015).


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