Relation of Circulating Levels of Human Immunodeficiency Virus (HIV) Antigen, Antibody to p24, and HIV-Containing Immune Complexes in HIV-Infected Patients

Immune complexes are formed in vivo when antigens are bound by antibodies as a normal consequence of immune reactions. These complexes are usually cleared from the circulation by Fc receptor-bearing cells that are widely distributed in the lymphoid system. In many autoimmune, infectious, and neoplastic diseases, however, immune complexes accumulate and cause significant pathological changes, such as inflammation, immunosuppression, and thrombocytopenia. Infection with the human immunodeficiency virus (HIV) predisposes the patient to other infectious agents, autoimmune phenomena, and neoplastic disease [1]. Because of these pathological changes, elevated levels of circulating immune complexes might be expected during HIV infection. In fact, numerous studies of patients infected with HIV have documented increases in immune complexes [1-4] and defects in the clearance of these complexes [5]. A few studies have also demonstrated the presence of HIV antigen or intact virus in these immune complexes [6-8]. To obtain a complete profile of serological responses to HIV, we measured circulating HIV antigen, antibody to p24, and HIV-containing immune complexes in selected groups of HIV-infected individuals. To make these measurements, we have developed a fluorescent, solid-phase, Clq-binding assay to detect antigen-specific immune complexes present during HIV infection. This assay has very high analytic sensitivity and uses a microsphere technique that we have previously described [9]. We report here the sensitivity and specificity of this assay and an analysis of the distribution of antigen-specific immune complexes in relation to levels of free HIV antigen in serum and antibody to p24 core.