PHYLOGENETIC SUBTYPES OF HUMAN T-LYMPHOTROPIC VIRUS TYPE-I AND THEIR RELATIONS TO THE ANTHROPOLOGICAL BACKGROUND

Isolates of human T-lymphotropic virus type I (HTLV-I) were phylogenet ically analyzed from native inhabitants in India and South America (Co lombia and Chile) and from Ainu (regarded as pure Japanese descendants from the preagricultural ''Jomon'' period). Their genomes were partia lly sequenced together with isolates from Gabon in central Africa and from Ghana in West Africa. The phylogenetic tree was constructed from the sequence data obtained and those of previously reported HTLV-I iso lates and simian T-lymphotropic virus type I (STLV-I) isolates. The he terogeneity of HTLV-I was recently recognized, and one major type, gen erally called the ''cosmopolitan'' type, contained Japanese, Caribbean , and West African isolates. The phylogenetic tree constructed in the present study has shown that this cosmopolitan type can be further gro uped into three lineages (subtypes A, B, and C). Subtype A consists of some Caribbean, two South American, and some Japanese isolates, inclu ding that from the Ainu, in addition to an Indian isolate, and subtype B consists of other Japanese isolates in addition to another Indian i solate, suggesting that there might be at least two ancestral lineages of the Japanese HTLV-I. Subtype A implies a close connection of the C aribbean and South American natives with the Japanese and thereby a po ssible migration of the lineage to the American continent via Beringia in the Paleolithic era. Subtype C consists of the West African and ot her Caribbean isolates, indicating that not all but part of the Caribb ean strains directly originated from West Africa probably during the p eriod of slave trade. The tree also has shown that the HTLV-I isolate from Gabon in central Africa forms a cluster with STLV-I from a chimpa nzee, suggesting a possible interspecies transmission between man and the chimpanzee in the past. No specific clustering was observed in the tree in relation to manifestations of the disease such as adult T-cel l leukemia and HTLV-I-related neurological disorders. Thus, the topolo gy of the phylogenetic tree reflects the movement of people carrying t he virus in the past.