Binding and adsorption of HIV-1–reactive antibodies and purified IgGs to GFP-293T^BaL cells. (A) Dot plots show mean fluorescence intensity (MFI) of staining by 51 HIV-1–reactive mAbs (y axis) tested on gp160Δc^BaL-expressing 293T cells versus IC₅₀ measured in TZM-bl assay using the BaL.26 pseudovirus. On the left, antibodies are grouped into those with no or low neutralizing activity (IC₅₀ > 50 µg/ml, black), and those that neutralize (IC₅₀ <50 µg/ml, red). On the right, the IC₅₀ values for neutralizing antibodies (IC₅₀ < 50 µg/ml) are shown. P-values were determined using the Mann-Whitney U test (left); correlation (right) was analyzed by Spearman correlation coefficient (rho). (B) As in A using IgG purified from the serum of 81 HIV-1–infected patients. (C) Graphs show the neutralization activity against BaL.26 of IgG from 4 patients (3B, 7A, 8A, and C69) after adsorption with 293T cells transfected with plasmids encoding gp160Δc^BaL (blue) or no-insert (green). Antibody binding to gp160Δc^BaL-expressing 293T cells (A and B) was measured in at least two independent experiments and one representative dataset is shown. Neutralization activity of adsorbed patients’ IgGs was analyzed in duplicate.