THE TRANSACTIVATOR GENE OF HUMAN T-CELL LEUKEMIA-VIRUS TYPE-I IS MOREVARIABLE WITHIN AND BETWEEN HEALTHY CARRIERS THAN PATIENTS WITH TROPICAL SPASTIC PARAPARESIS

Human T-cell leukemia virus type I (HTLV-I) causes T-cell leukemia and tropical spastic paraparesis (TSP) in a minority of infected people, whereas the majority remain healthy. No association between a particul ar HTLV-I sequence and disease manifestation has been found in previou s studies. We studied here the sequence variability of the gene for th e HTLV-I Tax protein, which is the dominant target antigen of the very strong cytotoxic T-lymphocyte response to the virus. In HTLV-I infect ion, the intraisolate nucleotide variability is much greater than the variability between isolates. The predicted protein sequence of Tax wa s significantly more variable in the healthy seropositive individuals' proviruses than in those of the patients with TSP. Thus, tax sequence heterogeneity, rather than the presence of particular sequences, dist inguishes healthy HTLV-I-seropositive individuals from patients with T SP.