Seroimmunology of AIDS retrovirus infection. I. Use of immunofluorescence assay to confirm sera with ELISA reactivity

One thousand sera shown to be reactive by one of two commercial enzyme linked immunosorbent assays (ELISA) for antibodies to the AIDS virus were referred to the NSW State Reference Laboratory for confirmatory assays. Each serum was retested by two commercial ELISA systems (Abbott and ENI), the ENI exclusionary H9 ELISA and an immunofluorescence assay. Three hundred and twenty four sera were reactive by all 3 tests whereas 244 demonstrated concordant non-reactivity. Three hundred and seventy seven sera were reactive by Abbott EIA only and could not be confirmed positive by the ENI ELISA incorporating exclusionary testing, immunofluorescence or Western immunoblot of representative sera. Sera obtained from teaching hospital laboratories were more likely to be positive and less likely to be negative by all 3 tests, and were also less likely to be Abbott EIA reactive only compared with sera obtained from the blood transfusion service. Of the remaining 55 sera, 52 demonstrated a negative immunofluorescent reaction or a pattern of equal fluorescence on AIDS virus infected and control cells. Representative sera were shown to be negative on Western immunoblot analysis. Of the 3 sera which demonstrated immunofluorescence reactivity, one was positive and one was negative by Western immunoblot, and one could not be determined. We conclude that a combination of two ELISAs, one with an exclusionary ELISA test and an immunofluorescence assay is a reliable and simple means of confirming reactive sera for AIDS virus antibodies.