Human retroviral env and gag polypeptides: serologic assays to measure infection

Humoral antiviral responses to human retrovirus infections identify persistently infected individuals and can be used to characterize virus-host interactions. Antibodies to native viral polypeptides have been reliably measured, although quantitation of env antibodies is difficult due to a lack of purified antigens. To quantitate antibodies to env antigens, bacterially expressed cloned env polypeptides from the transmembrane regions of human T lymphotropic virus types I and III were applied to nitrocellulose filters in an immunodot assay. A combination of the sensitivity of the Western blot procedure and the specificity of peptides from defined viral sequences was used to detect 49/49 HTLV-III/LAV-infected individuals previously defined as seropositive by radioimmunoprecipitation sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Of these HTLV-III/LAV envelope seropositive people, 22% lacked antibody to p24 in a radioimmunoassay. In contrast, the sensitivity of antibody detection to HTLV-I env antigens and p24 were comparable. Antibodies to HTLV-I and HTLV-III/LAV env transmembrane peptides were not cross-reactive. Levels of antibody to env antigens of both HTLV-I and HTLV-III/LAV persisted without change for at least 26 mo, suggesting that most infections represent stable virus-host interactions. The use of bacterially expressed env peptides offers a rapid serologic approach for distinguishing human retroviral infections and can be used to define immune responses to specific regions of the viral genome.