Flow cytometric analysis of bcl-2 expression in SMS-SB cells. SMS-SB cells were cultured as described in the legend to Fig 3, harvested and washed. The cells were gently permeabilized in 0.1% (wt/vol) saponin-containing buffer and treated with monoclonal anti-bcl-2 antibody. After incubation for 20 minutes on ice, the cells were washed and an aliquot of FITC-anti-mouse IgG added to visualize the primary MoAb. After further incubation and washing, the cells were treated with 100 μg/mL propidium iodide and immediately analyzed by flow cytometry. In the dot plots illustrated, the X-axis illustrates propidium iodide staining in linear units of fluorescence, while the Y-axis represents bcl-2 staining on a logarithmic scale. The experiment shown is representative of three repeats. (A) Normal cell density. (B) Low cell density. (C) Low cell density + 100 ng/mL sCD23.