Mack S J, Erlich H A
Department of Molecular and Cell Biology, University of California at Berkeley, USA.
Tissue Antigens. 1998 Jan;51(1):41-50. doi: 10.1111/j.1399-0039.1998.tb02945.x.
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 DRB108 variant, DRB10807, 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 DRB10807 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 DRB10807 heterozygotes, is considered with the high frequency of the DRB10807 and DPB11401 alleles, we infer that native South American populations may have been under selection pressure for increased allele diversity.
采用聚合酶链反应/序列特异性寡核苷酸探针杂交法（PCR/SSO）和DNA测序技术，对生活在巴西的南美原住民提库纳族的49名个体的人类白细胞抗原II类基因座HLA-DRB1、DQA1、DQB1和DPB1的等位基因进行了测定。在提库纳族中，发现了一种新描述的DRB108变异体DRB10807，此前仅在哥伦比亚原住民以及非洲和高加索裔的当代巴西人中报道过，其出现频率较高（f = 0.225）。由于0807仅在南美人群中被观察到，我们推测它是在南美各原住民群体隔离之后，最近从亲本0802等位基因产生的，并推断DRB10807等位基因是由祖先0802的第57密码子处的C到T变化（天冬氨酸→缬氨酸，GAT→GTT）产生的。DRB1基因第二内含子中一个复杂的可变数目串联重复序列（VNTR）的序列支持了这一推断。DPB1等位基因0401、0402和1401占观察到的提库纳族DPB1等位基因的76%（频率分别为0.166、0.427和0.166）。此外，在其他一些南美原住民群体中也观察到的DPB1等位基因3501，其出现频率为0.053，可能是由南美假定的祖先等位基因1401产生的。提库纳族的DRB1和DPB1等位基因频率偏离了预期的哈迪-温伯格平衡比例，而DQA1和DQB1等位基因频率则没有。当考虑到这种涉及观察到的DRB10807杂合子过量的偏差以及DRB10807和DPB11401等位基因的高频率时，我们推断南美原住民群体可能一直处于增加等位基因多样性的选择压力之下。
