Bcl-2 and Bcl-X expression was evaluated by cytoplasmic immunofluorescence in CD14⁺CD34⁺ cells before or after 1-hour adhesion on D12P (PECAM-1⁺) or mock-transfected NIH3T3 monolayers, in the absence or presence of the F(ab′)₂ of the specific anti–PECAM-1 mAb (5 μg/mL), collected after an additional 36 hours of culture. Cells were fixed in 2% paraformaldehyde, permeabilized with 0.01% NP-40, stained with the specific FITC anti–Bcl-2 or FITC anti–Bcl-X mAbs, and run on a FACSort. At least 10⁴ cells per sample were analyzed and results plotted as arbitrary units (au) of mean fluorescence intensity (MFI, mean ± SD from 8 experiments). MFI of cells stained with an FITC-irrelevant mAb was 10 ± 5 au.