Phylogenetic characterization of a new HTLV type 1 from the Ainu in Japan

Human T cell leukemia virus type 1 (HTLV-1) is endemic among three ethnically distinguishable populations in Japan (the Ainu, Ryukyuans, and Wajin), which, together, account for most of the population in Japan. While much is known about the phylogeny of the Ryukyuan and Wajin strains of HTLV-1, only one Ainu strain has been phylogenetically analyzed. We report here a new HTLV-1 strain from the Ainu. The new isolate (U8306), as well as the previously reported isolate, are members of the Cosmopolitan group and further belong to the Transcontinental subgroup. This subgroup also predominates among the Ryukyuans, whereas the Japanese subgroup is the major subgroup among the Wajin. The predominance of subgroup A in the Ainu and Ryukyuans suggests that they share a common origin of HTLV-1.