FIG. 4.
Thermal treatment of HIV-1 results in exposure of the cryptic CD4-induced epitope. HIVSX and HIVNL4-3 were prepared in serum-free medium following infection of a three-donor pool of PBMC. Clarified culture supernatants containing 200 ng of HIV p24 per ml were aliquoted for single use. HIVSX and HIVNL4-3 were each used at 16 ng/well. Samples treated with sCD4 to induce exposure of the 17b epitope were preincubated with 2 ng of sCD4 per well in PBS with 0.2% BSA for 30 min at 37°C. MAb 17b was incubated with HIVSX at a concentration of 2 μg/ml and with HIVNL4-3 at a concentration of 10 μg/ml. Thermal treatment of HIV-1 was performed by loading samples into tubes and heating them for 30 min at 62°C in a heat block filled with water. Binding to 17b was assessed by capture ELISA. Data are expressed as percent binding to 17b. Mean ± standard error are shown for three independent experiments. (A) HIVSX (OD was 1.4 for gp120 in untreated sample); (b) HIVNL4-3 (OD was 1.01 for gp120 in untreated sample).