Detection of human immunodeficiency virus core protein in plasma by enzyme immunoassay. Association of antigenemia with symptomatic disease and T-helper cell depletion.

A sensitive enzyme immunoassay was developed for detecting human immunodeficiency virus (HIV) core antigen. Assay sensitivity was 3.67 pmol/L of purified HIV core protein, and 1 or 100 in-vitro infectious units/mL of HIV in purified virus preparations or cell culture supernatants, respectively. Enzyme immunoassay sensitivity exceeded that of reverse transcriptase assay by 1000-fold. Core antigen was detected in whole plasma from 41% of symptomatic subjects and 13% of asymptomatic subjects seropositive for HIV. After plasma fractionation, antigenemia was found in 60% of symptomatic subjects and in 33% of asymptomatic subjects seropositive for HIV. Fifty-seven percent of samples from which HIV could be isolated in lymphocyte culture had detectable quantities of core antigen in plasma. However, at least 87% of samples with measurable antigen in plasma had HIV isolated from lymphocyte cultures. Antigenemia was associated with reduced T-cell number and symptomatic disease, and may be a useful marker for disease progression.