Molecular characterization and phylogenetic analyses of a new, highly divergent simian T-cell lymphotropic virus type 1 (STLV-1marc1) in Macaca arctoides.

A serological survey of a captive colony of Asian monkeys indicated that six Macaca arctoides had antibodies to human T-cell leukemia/lymphotropic viruses (HTLV). Over a 4-year interval, sera from these animals continued to exhibit a peculiar Western blot (WB) pattern resembling an HTLV-2 pattern (p24gag reactivity of equal or greater intensity than that of p19gag and a strong reactivity to recombinant gp21) but also exhibiting, in five of six cases, a reactivity against MTA-1, an HTLV-1 gp46 peptide. PCR experiments on DNA extracted from peripheral blood mononuclear cells using HTLV-1- or HTLV-2-specific long terminal repeat, gag, pol, env, and tax primers yielded negative results. However, highly conserved primers successfully amplified three different gene segments of env, tax, and env-tax. The results of comparative sequence analysis demonstrated that STLV-1marc1 was not closely related to any known STLV-1 strain, was the most divergent strain of the HTLV-1-STLV-1 group, and lacked the ATG initiation codons corresponding to the p12 and p13 proteins of HTLV-1. Phylogenetic analyses incorporating representative strains of all known HTLV-STLV clades consistently depicted STLV-1marc1 within the HTLV-1-STLV-1 type 1 lineage, but it probably diverged early, since its position is clearly different from all known viral strains of this group and it had a bootstrap resampling value of 100%. Genetic distance estimates between STLV-1marc1 and all other type 1 viruses were of the same order of magnitude as those between STLV-2PanP and all other type 2 viruses. In light of the recent demonstration of interspecies transmission of some STLV-1 strains, our results suggest the existence in Asia of HTLV-1 strains related to this new divergent STLV-1marc1 strain, which may be derived from a common ancestor early in the evolution of the type 1 viruses and could be therefore considered a prototype of a new HTLV-STLV clade.