Contribution of polymerase chain reaction and radioimmunoprecipitation assay in the confirmation of human T-lymphotropic virus infection in French blood donors. Retrovirus Study Group of the French Society of Blood Transfusion.

Background: To verify the criteria for human T-lymphotropic virus (HTLV) seropositivity in Western blot (WB) proposed by the Retrovirus Study Group of the French Society of Blood Transfusion, 186 blood donations that were repeatably reactive in HTLV enzyme-linked immunosorbent assay, selected according to their WB pattern, were tested by polymerase chain reaction (PCR) and radioimmunoprecipitation assay (RIPA). Study Design and Methods: In two commercially available WBs, 12 samples were confirmed as positive (rgp21+p19+p24) and 174 were interpreted as indeterminate (one or two reactivities to these proteins). The primer pairs used for the PCR allowed the amplification of type I (HTLV-I) or type II (HTLV-II) (or both) sequences, The RIPA was performed with two 35S-labeled cell lines: HTLV-I infected HUT 102/82 and HTLV-II-infected MoT. Results: Of the 12 positive samples, 11 were classified as HTLV-I-positive and one as HTLV-II-positive. Among the 174 indeterminate samples, three (WB pattern: rgp21+, p19+, p24-) were HTLV-I positive in PCR (one of them was positive in RIPA also); the other 171 were HTLV negative. Conclusion: In the study of a population in which 97 percent of HTLV infections are due to HTLV-I, these data support the three-protein criteria (rgp21; p19, and p24) for a positive blot reading. No HTLV infection was observed when rgp21 did not react, Consequently, p19 and/or p24 band patterns represent false reactivity and do not require PCR or RIPA confirmation. To discriminate between false- and true-positive results in the absence of MTA-1 or K55 reactivity, PCR and/or RIPA is required only when rgp21 reactivity is associated with one gag band (p19 or p24).