ENZYME-LINKED IMMUNOASSAY FOR HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ENVELOPE GLYCOPROTEIN-120

An enzyme-linked immunosorbent assay (ELISA) that can measure picogram quantities of human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein 120 (gp 120) in cell culture medium or body fluids has been developed. Recombinant, soluble CD4 immobilized in microtiter trays was used to capture gp120, which was then detected with polyclonal sheep antibody to gp 120 followed by biotinylated rabbit anti-sheep immunoglobulin G and an avidin-alkaline phosphatase indicator system. With a reference recombinant gp120, the assay showed a linear relationship between optical density and concentrations ranging from 60 to 6,000 pg/100-mu-l well; precision of the assay varied with the concentrations and ranged from +/- 40% with amounts smaller than 200 pg to +/- 10% with amounts larger than 200 pg. In a group of coded samples containing 60 pg (approximately 10(7) molecules) of reference gp 120, the assay correctly identified the samples as containing gp 120 99% of the time, with no false-positive results recorded for blank samples. Recombinant gp 120 prepared in another cell culture system demonstrated a binding coefficient 13-fold lower than that of reference gp 120. Mixing standard amounts of reference gp 120 with increasing concentrations of human sera reduced assay sensitivity, although the linear relationship between gp 120 concentration and optical density remained. With this assay we were able to detect gp 120 in HIV-1 suspensions prepared from cultured lymphoblastoid cells and in the sera of HIV-1-infected patients. This ELISA for gp 120 should be useful for studying the biological role of gp 120 in HIV infection.