摘要：HLA-DRB1 polymorphism was investigated by molecular DNA-based typing in 37 Tongans living on Ha’ano island of the Ha’apai group. The predominant HLA-DRB1 alleles were DRB1*0901 (20.3%) and DRB1*0403 (18.9%). A principal component analysis of the DRB1 allele frequencies discriminated between the Polynesians and other Oceanian populations, including Melanesians, Micronesians, and Australian Aborigines. Both present and previous studies have shown that the allele frequency of DRB1*0901 is markedly high in Polynesians and Asians, while this allele is seldom found in Non-Austronesian (NAN)-speaking Melanesians, Micronesians, and Australian Aborigines. Furthermore, we analyzed the frequencies of allele coding for Arg at position 196 ( 196R : nucleotide [nt] 587G) of tumor necrosis factor receptor 2 ( TNFR2 , TNF-R75 ) in three Oceanian populations: Tongans, Austronesian (AN)-speaking Balopa islanders living in Manus province of Papua New Guinea, and NAN-speaking Gidra living in the southwestern lowlands of Papua New Guinea. The frequencies of the TNFR2-196R allele, observed at a relatively high frequency in East and Southeast Asian populations, were 24.0%, 7.3%, and 1.0% in the Tongans, Balopa islanders, and Gidra, respectively. Considering that the allele frequencies of DRB1*0901 and TNFR2 196R are relatively high in Asians, Polynesians, and AN-speaking Melanesians (Balopa islanders), but very low in NAN-speaking Melanesians (Gidra), we conclude that at least part of the AN-speaking Polynesian ancestors were derived from Asian populations, and that extensive gene flow from the Polynesian ancestors to the indigenous Melanesians occurred around their initial migration to Melanesia. This is consistent with the results from analyses of mitochondrial DNA and ABO blood group gene polymorphisms in the same study populations.
