Confirmatory tests for human T-cell leukemia virus type 1 (HTLV-1): western blot compared with RIPA on African sera.

Confirmation of human T-Cell leukemia virus type 1 (HTLV-1) seropositivity calls for reactivity against at least 2 proteins encoded by 2 different genes, revealed by Western blot (WB) and/or radioimmuno-precipitation assay (RIPA). To evaluate the use of WB as a basis for applying these criteria, we conducted a study of two types of WB and compared them with RIPA patterns. The first part of the work, performed with 40 African sera, used Dupont de Nemours commercialized WB and an 'in-house' WB. Both WB detected antibody to proteins encoded by 2 different genes: antibody to gag products were revealed equally by both WB, but commercialized WB detected antibody to tax protein whereas the 'in-house' WB detected antibody to env protein (gp46) more efficiently. The second part of the work, conducted with 158 African sera, compared results of an 'in-house' virus lysate WB and RIPA. Our data show a perfect concordance between the two procedures when sera were clearly positive by WB (gag + env reaction). Sera reacting to p19 and p24 (both gag) by WB were confirmed positive by RIPA in 75% of the cases. The majority of the indeterminate WB profiles not confirmed by RIPA presented isolated gag reactivity (p15 or p19 or p24).