ENZYME-LINKED IMMUNOSORBENT ASSAYS FOR THE MEASUREMENT OF HUMAN-IMMUNODEFICIENCY-VIRUS, TYPE-1 REVERSE-TRANSCRIPTASE ANTIGEN AND ANTIBODIES

Enzyme-linked immunosorbent assays (ELISA), using recombinant HIV-1 reverse transcriptase (RT; p66), are described for the measurement of RT antigen and serum antibodies to RT (anti-RT). The ELISA for anti-RT was developed in qualitative and quantitative forms, both were highly specific (100%, 0/859; 99.6%, 3/859), the former was sensitive (100%, 364/364) detecting the highest dilution of a standard high titre anti-HIV-1 RT antibody positive control serum. The latter was less sensitive (97.2%, 354/364) detecting lower dilutions of the antibody control, but had the advantage of producing highly reproducible optical density/concentration curves for the quantification of unknown anti-RT samples. In a cross-sectional study of 191 patients with HIV-1 infection, all patients developed anti-RT antibodies in CDC disease group II and III that declined but persisted in all cases into CDC disease group IV. The RT antigen assay was specific (100%, 0/772) and sensitive detecting 6 to 15 pg/ml of recombinant RT antigen diluted in normal human serum. No cross-reactivity using the RT antibody and antigen assays was seen in sera from 85 patients with current or previous hepatitis B infection or 21 sera from patients with HIV-2 infection. Further, no reactivity was demonstrated with the assays in a cohort of 20 seronegative partners (320 samples) exposed to HIV-1 infection over a 4-yr period. In samples from a patient with documented seroconversion, RT antigen was the first detectable marker of HIV-1 infection and was followed by a prompt anti-RT response. Serum RT antigen disappeared or remained low in most patients during CDC disease group II and III and rarely reappeared with progression to CDC disease group IV. In tissue culture studies RT antigen was detected in supernatant within 12 h (75 pg/ml), gave an initial peak at 36 h (300 pg/ml) and then continued to rise up to 5 days (603 pg/ml), offering a simple, cost-effective alternative to existing methods.