Differences in HLA class II alleles of isolated South American Indian populations from Brazil and Argentina.

We have studied the HLA class II alleles in 277 South American Indians, which included Argentinian tribes from the Gran Chaco: Toba (n = 135), Toba-Pilaga (n = 19), Mataco-Wichi (n = 49), and Xavantes, a tribe from Central Brazil (n = 74). In the Brazilian tribe, only four DR groups were found: DRB11602 (gf = 0.303), DRB104 including DRB10404 (gf = 0.070) and DRB10407 (gf = 0.077), DRB10802 (gf = 0.265), and DRB11402 (gf = 0.303). The HLA class II allele frequencies were similar among the different Argentinian tribes, and 90% of DRB1 alleles belonged to three families: DRB104 (including DRB10403, DRB10404, DRB10407, DRB10411, and DRB10417), DRB10802, and DRB114 (including DRB11402 and DRB11406). At the DPB1 locus, we found only seven alleles, the most frequent being DPB10402. Comparison of HLA class II alleles with those of North American Indians that we have previously studied shows that the frequency of some HLA class II alleles in Brazilian Xavantes resembles that of North American Indians more than that of the Argentinian Indian tribes. The allele DRB10417 was found exclusively in this population.