IMPROVED DETECTION OF SERUM HIV P24 ANTIGEN AFTER ACID DISSOCIATION OF IMMUNE-COMPLEXES

Objective: To evaluate an acid pretreatment method designed to dissoci ate HIV p24 antigen from immune complexes in serum. Design: Patient se ra and sera containing experimental immune complexes were quantified f or p24 antigen before and after immune complex dissociation (ICD). The clinical application of ICD was assessed in 1328 serum and plasma sam ples collected from HIV-infected patients. Methods: Immune complexes w ere created artificially by mixing purified p24 antigen with antibody- positive sera or a standardized concentration of human antibody to p24 . ICD was achieved by incubation of samples with an equal volume of Gl ycine HCl for 90 min at 37-degrees-C followed by neutralization with T ris NaOH. Samples were quantified for p24 antigen using a commercial e nzyme-linked immunosorbent assay (ELISA) kit. Results: ICD resulted in significant release of purified antigen from simulated immune complex es in antibody-positive sera. Variation in antigen sequestration and d issociation was related to anti-gag antibody titers. ICD resulted in c omplete recovery of 500 pg of antigen complexed with human anti-p24 an tibody at concentrations up to 2.5 U/ml. In seropositive patients, the mean level of serum antigen was 3.5-fold higher after ICD, and an add itional 21% were antigen-positive. Conclusions: Pretreatment greatly i mproved antigen detection in HIV-antibody-positive sera by effectively dissociating immune complexes without compromising reactivity of the antigen itself. The treatment also facilitated routine monitoring of p atients by revealing fluctuations in serum antigen that were indisting uishable or poorly defined in untreated sera.