Optimal conditions of immune complex transfer enzyme immunoassay for p24 antigen of HIV-1.

In the immune complex transfer enzyme immunoassay for HIV-1 p24 antigen, different preparations of anti-p24 Fab'-beta-D-galactosidase conjugate, various periods of time for immunoreactions involved, and shaking for incubations with polystyrene beads were tested. On the basis of the results of these experiments, p24 antigen was measured as follows. The antigen was reacted simultaneously with 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate and highly polymerized monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate at 37 degrees C for 2 hr. The immune complex formed comprising the three components was trapped onto colored polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG for 1.5 hr and was transferred to white polystyrene beads coated with streptavidin in the presence of epsilon N-2,4-dinitrophenyl-L-lysine for 1.5 hr. The incubations with polystyrene beads were performed at room temperature with shaking. beta-D-Galactosidase activity bound to the white polystyrene beads was assayed by fluorometry at 30 degrees C for 2 hr. The detection limit of p24 antigen (0.1 amol/tube and 10 amol (0.24 pg)/ml of serum) was equal to that obtained when the formation, trapping, and transferring of the immune complex were performed for 4, 16, and 3 hr, respectively, by incubation without shaking. Namely, the period of time required for the immune complex transfer enzyme immunoassay of p24 antigen was markedly shortened (25.5-7 hr) without loss of the sensitivity. By the improved immune complex transfer enzyme immunoassay, p24 antigen was detected 12-20 days earlier than the detection of antibodies to HIV-1, i.e., seroconversion by the conventional ELISA.