Unusual HLA-B alleles in two tribes of Brazilian Indians

Abstract

The Kaingang and Guarani are culturally and linguistically distinct tribes of southern Brazil. Like all Amerindian groups they show limited HLA polymorphism, which probably reflects the small founder populations that colonized America by overland migration from Asia 11,000-40,000 years ago. We find the nucleotide sequences of HLA-B alleles from the Kaingang and Guarani to be distinct from those characterized in caucasian, oriental and other populations. By comparison, the HLA-A and C alleles are familiar. These results and those reported in the accompanying paper on the Waorani of Ecuador reveal that a marked evolution of HLA-B has occurred since humans first entered South America. New alleles have been formed through recombination between pre-existing alleles, not by point mutation, giving rise to distinctive diversification of HLA-B in different South American Indian tribes.

High frequencies of alleles MICA*020 and MICA*027 in Amerindians and evidence of positive selection on exon 3

“…Guarani and Kaingang live close to each other but have remarkable genetic and cultural differences. 24,25 Another important feature of these populations is that gene flow from non-Amerindian and other Amerindian populations is low, with the exception of Guarani Ñ andeva, whose admixture was estimated as 14%. 25,26 The aim of this study was to describe STR_MICA and MICA allelic frequencies and MICA-HLA-B-HLA-C associations in the Guarani and Kaingang populations from Brazil, to compare the diversity found with that of other populations and to extract information about the evolution of MICA polymorphism.…”

Evidence for an ancient selective sweep in the MHC class I gene repertoire of chimpanzees

“…1B). Hence, recombination appears to affect the order of intron-exon sequences, as found for HLA-B exons (16,31,32). Only members of HLA-B*08, -B*27, and -B*35 seem to have lineage unique intron 2 sequences.…”

How large was the founding population of Darwin's finches?

“…It has indeed been claimed, for example, that human Mhc class I loci evolve rapidly in certain South American Indian populations because of selection pressure exerted by the environment (Belich et al 1992 ;Watkins et al 1992). We have, therefore, considered the possibility that most of the Mhc polymorphism now found in the Darwin's finches arose by mutation and has been maintained by selection after the colonization of the Gala!…”