Binding of Env-specific MAbs and HIV-1+ serum antibodies to HIV-1-infected and uninfected primary CD4+ T cells. (A) Primary CD4+ T cells infected with the GFP reporter HIV-1ADA strain were stained at 48 h postinfection with the MAbs A32 (CD4i cluster A), 2G12 (CD4-independent outer domain epitope), PGT126 (N332 glycosylation site on the V3 loop), and 3BNC117 (CD4 binding site) at 5 μg/ml. (B) Primary CD4+ T cells infected with the transmitted/founder HIV-1 infectious molecular clone CH077.t were stained at 18 h postinfection with HIV-1+ serum (1:1,000; n = 3) and the MAbs A32, PGT126, and PGT151 (gp120-gp41 interface) at 5 μg/ml. The bar graphs depict mean values obtained from three independent experiments, with error bars showing standard errors of the means. Cell populations are indicated on the figure. The binding of Env-specific MAbs and HIV-1+ serum antibodies was determined using flow cytometry, and results are presented as MFI values. N− U−, cells infected with Nef- and Vpu-deficient HIV-1.