CD4 epitope expression on neutrophils and PBMCs and neutrophil binding of HIV-1 gp 120. (A) Histogram plots depicting overlaid fluorescence intensities of purified PBMCs and neutrophils from an HIV-uninfected control after indirect staining with the anti-CD4 mAbs OKT4, 13B8-2, and C9E11. The control histogram derives from cells stained with second-step reagent only. (B) The histogram plots show the fluorescence intensities of purified neutrophils stained with FITC-directly-conjugated gp120; streptavidin-FITC was used as control.