Molecular Evidence of Human T-cell Lymphotropic Virus Types 1 and 2 (HTLV-1 and HTLV-2) Infections in HTLV Seroindeterminate Individuals from São Paulo, Brazil

Background: Using enzyme immunoassays and Western blot (Wb) tests, HTLV serodiagnosis yields indeterminate results in a significant number of cases.

Objective: To determine the prevalence of HTLV infection among HTLV-seroindeterminate individuals.

Study Design: We studied peripheral blood mononuclear cells from 65 anti-HTLV Wb-seroindeterminate individuals by attempting to amplify proviral DNA sequences (tax and pol) to identify HTLV-1 and HTLV-2 infections.

Results: These 65 specimens exhibited predominantly (43%) anti-HTLV antibodies to gag-coded antigens in the absence of anti-p24 on Wb analysis. Tax proviral sequences were detected in 6 (9.2%) samples. According to restricted fragment polymorphism analysis (RFLP), we identified HTLV-1 proviral DNA in 4 samples, HTLV-2 in one and sequences from both in another. Nested PCR for the pol region was positive in 3 (4.6%) specimens, which were also positive for tax sequences. After hybridization HTLV-1 infection was confirmed in 2 samples (3.1%) and HTLV-2 in another (1.5%). Detection of a single HTLV DNA sequence may be due to infection by defective provirus, but its significance remains undefined. In this cohort, no Wb reactivity pattern was predictive of proviral detection. HTLV-1 infection was demonstrated in an individual who had Wb reactivity to gag-coded antigens only.

Conclusions: This emphasizes the importance of clinical and laboratory follow-up of HTLV-seroindeterminate individuals from endemic areas.