A simple method for improved assay demonstrates that HIV p24 antigen is present as immune complexes in most sera from HIV-infected individuals.

Improved detection and quantitation of p24 antigen of the human immunodeficiency virus (HIV) in sera was obtained by pH 2.5-3.0 pretreatment of samples before using a standard HIV p24 antigen ELISA. Pretreatment dissociated immune complexes and denatured antibodies with little or no compromise of p24 antigen immunoreactivity. For 652 HIV antibody-positive sera, direct comparison of the pretreatment with the conventional assay demonstrated substantial increase in both antigen positivity (50.6% vs. 12.4%) and in the level of p24 antigen in sera. Serum HIV antigen is mainly in the form of immune complexes in most individuals at all stages of HIV infection. Longitudinal study of 1 year (three measurements) on 29 seroconverters demonstrated two main patterns of p24 antigen expression in sera: 34.5% of infected individuals never express any form of detectable HIV antigen and 58.6% persistently demonstrate serum p24 antigen, usually in complex with antibody. Only 6.9% show episodic p24 antigen positivity.