HLA class II polymorphism in the Ticuna of Brazil: evolutionary implications of the DRB1*0807 allele

Tissue Antigens. 1998 Jan;51(1):41-50. doi: 10.1111/j.1399-0039.1998.tb02945.x.

Abstract

The alleles at the HLA class II loci HLA-DRB1, DQA1, DQB1 and DPB1 were determined for 49 individuals of the Ticuna, a Native South American population living in Brazil, using PCR/SSO probe hybridization and DNA sequencing. A newly described DRB1*08 variant, DRB1*0807, which has previously been reported only in native Colombians and contemporary Brazilians of African and Caucasian descent, was identified in the Ticuna at a high frequency (f=0.225). Because *0807 has been observed only in South American populations, we propose that it was generated from a parental *0802 allele recently, after the isolation of various Native South American populations, and infer that the DRB1*0807 allele was generated by a C to T change at codon 57 (Asp-->Val, GAT-->GTT) from the ancestral *0802. This inference is supported by the sequence of a complex VNTR in the second intron of the DRB1 gene. The DPB1 alleles *0401, *0402 and *1401 constituted 76% of the observed Ticuna DPB1 alleles (f=0.166, 0.427 and 0.166 respectively). In addition, the DPB1 allele *3501, which has been observed in a few other Native South American groups, was observed at a frequency of 0.053 and may have been generated from the putative ancestral allele *1401 allele in South America. The DRB1 and DPB1 allele frequencies for the Ticuna deviate from expected Hardy-Weinberg equilibrium proportions, while DQA1 and DQB1 allele frequencies do not. When this deviation, which involves an observed excess of DRB1*0807 heterozygotes, is considered with the high frequency of the DRB1*0807 and DPB1*1401 alleles, we infer that native South American populations may have been under selection pressure for increased allele diversity.

MeSH terms

  • Africa
  • Alleles*
  • Brazil / ethnology
  • Chromosome Mapping
  • DNA, Mitochondrial
  • Evolution, Molecular*
  • Gene Frequency
  • HLA-DP Antigens / genetics
  • HLA-DP beta-Chains
  • HLA-DQ Antigens / genetics
  • HLA-DQ alpha-Chains
  • HLA-DQ beta-Chains
  • HLA-DR Antigens / genetics*
  • HLA-DRB1 Chains
  • Haplotypes
  • Homozygote
  • Humans
  • Indians, South American / genetics*
  • Linkage Disequilibrium
  • Models, Genetic
  • Polymorphism, Genetic*

Substances

  • DNA, Mitochondrial
  • HLA-DP Antigens
  • HLA-DP beta-Chains
  • HLA-DPB1 antigen
  • HLA-DQ Antigens
  • HLA-DQ alpha-Chains
  • HLA-DQ beta-Chains
  • HLA-DQA1 antigen
  • HLA-DQB1 antigen
  • HLA-DR Antigens
  • HLA-DRB1 Chains