Human T lymphotropic virus types I and II proviral sequences in Argentinian blood donors with indeterminate western blot patterns

Human T-cell lymphotropic virus (HTLV) seroindeterminate blood donors have been reported worldwide including Argentina. To investigate the significance of HTLV-I/II seroindeterminate Western blot (WB) patterns, we conducted an 8-year cross-sectional study. Of 86,238 Argentinian blood donors, 146 sera were reactive by screening tests. The WB results indicated that 20% were HTLV-I reactive, 8% HTLV-II reactive, 61% indeterminate, and 11% negative. The overall sero-prevalence was 0.034% for HTLV-I, 0.014% for HTLV-II, and 0.103% for indeterminate. In 57 reactive specimens, HTLV-I/II provirus could be examined by type specific PCR for tax, pol, and env regions. When at least two gene fragments were amplified HTLV-I/II infection was considered confirmed. PCR results confirmed all WB seropositive samples for HTLV-I (n = 15), and HTLV-II (n = 7), and the only WB negative case was also PCR negative, showing a complete concordance between PCR and WB. However, of 34 WB seroindeterminate sera studied by PCR, in 5 was proviral DNA amplified. According to our criteria PCR confirmed one to be HTLV-I, and one HTLV-II, 3 remained indeterminate since only tax sequences were amplified. Among WB indeterminate samples tested by PCR, most of their serological profile showed reactivity to gag codified proteins but lacked env reactivities (70%). One sample with a WB gag pattern showed proviral tax sequences, but of the four samples with reactivity to env proteins GD21 (n = 3) or rgp4611 (n = 1) PCR results indicated that one was HTLV-I, one was HTLV-II, and two were indeterminate (only tax sequences). In conclusion, the majority of HTLV-seroindeterminate WB donors exhibited a gag indeterminate profile lacking HTLV provirus, and were thus considered uninfected. However, seroreactivity to env proteins, in particular to GD21, may indicate infection and a follow-up study of each seroreactive blood donor should be considered.