Serologic characterization of human immunodeficiency virus infection by Western blot and radioimmunoprecipitation assays

The Western blot and radioimmunoprecipitation assay (RIPA) appear to be the most specific tests available for the detection of antibodies directed against human immunodeficiency virus (HIV). An investigation of 678 HIV-seropositive samples from 518 patients by the Western blot assay indicates that the majority of patients who have been exposed to HIV exhibit antibodies directed against glycoprotein (gp) 41. The HIV-seropositive samples were categorized into four groups according to their Western blot antibody reactive patterns. Group 1 had evidence of reactivities directed against protein (p) 24 and gp41; group 2 had reactivity to gp41 and no reactivity to p24; group 3 had reactivity to p24 and p55 and no reactivity to gp41; and group 4 had an isolated p24 reactivity. The RIPA revealed antibody reactivities directed against HIV envelope proteins (gp 160, gp 120, and gp41) in 91 of 95 samples that were tested. No HIV antibody reactivities were detected by RIPA in four samples from group 4. Specimens exhibiting an isolated antibody reactivity directed against p24 by Western blot analysis should have further evaluation before being labeled as indicative of HIV exposure. A western blot study on a subsequent sequential sample or another confirmatory assay, such as the RIPA, should be performed to identify antibodies directed against HIV envelope components.