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.

The HLA-A, B, C, DR and DQ antigens of 240 Kaingang and 98 Guarani individuals have been characterized. The most frequent antigens found among the Kaingang are A31, 2, 24; B35, 51, 39, 48; Cw4, 7, 3, 1; DR8, 4, 2; DQ blank, 3. In the Guarani, they are A2, 28, 31; B40, 62, "53G"; Cw3, 4; DR2, 4, 8, 6; DQ3, blank. B " 53G" is an unusual antigen of the B5 cross-reactive group. DQ blank possibly corresponds to DQ4, not tested in this study. The reaction patterns of B35, B40 and DR4 indicate intra-tribal (of B35 and B40), and inter-tribal (DR4, B40 and B35) heterogeneity of these antigens. 408 Kaingang and 141 Guarani haplotypes were defined by segregation analysis. Of the commonest 10 Guarani and 9 Kaingang haplotypes, only one is shared by both tribes. Significant, positive linkage disequilibrium values for HLA-A,B; HLA-A,C; HLA-B,DR and most HLA-B,C antigen pairs were also different for the two populations. Genetic distance estimates between these two and another seven South-American Indian populations, and relative to the major human races (negroids, caucasoids, and mongoloids) reveal a comparatively high degree of divergence between the Kaingang and the Guarani, which is uncommon for Amerindian populations living close one to another.

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