MOLECULAR CHARACTERIZATION AND PHYLOGENETIC ANALYSES OF A NEW, HIGHLYDIVERGENT SIMIAN T-CELL LYMPHOTROPIC VIRUS TYPE-1 (STLV-1MARC1) IN MACACA ARCTOIDES

A serological sun ey of a captive colony of Asian monkeys indicated th at six Macaca arctoides had antibodies to human T-cell leukemia/lympho tropic 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 (p24(gag) reactivity of equal or greater intensity t han that of p19(gag) 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 termina l repeat, gag, pal, env, and tax primers yielded negative results, How ever, highly conserved primers successfully amplified three different gene segments of env, tax, and env-tax. The results of comparative seq uence analysis demonstrated that STLV-1marc1 was not closely related t o 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 t he p12 and p13 proteins of HTLV-1. Phylogenetic analyses incorporating representative strains of all known HTLV-STLV clades consistently dep icted STLV-1marc1 within the HTLV-1-STLV-1 type 1 lineage, but it prob ably diverged early, since its position is clearly different from all known viral strains of this group and it had a bootstrap resampling va lue of 100%. Genetic distance estimates between STLV-1marc1 and all ot her type I viruses were of the same order of magnitude as those betwee n STLV-2PanP and all other type 2 viruses, In light of the recent demo nstration of interspecies transmission of some STLV-1 strains, our res ults suggest the existence in Asia of HTLV-1 strains related to this n ew divergent STLV-1marc1 strain, which may be derived from a common an cestor ear ly in the evolution of the type I viruses and could be ther efore considered a prototype of a new HTLV-STLV clade.