MO7e cells were cultured in IMDM supplemented with 1% FCS and 0.5% GM-CSF for 16 hours, treated without or with PP1 (10 μmol/L) for 30 minutes at 37°C, labeled with the 104D2 MoAb (5 μm/mL) for 45 minutes at 4°C, treated with SCF (200 ng/mL) for 0, 1, 3, or 5 minutes at 37°C, fixed, and labeled with goat antimouse IgG-FITC plus propidium iodide. The proportion of cells exhibiting a fluorescent cap in one region of the cell was determined using a Zeiss fluorescent microscope. For each data point, 50 to 90 cells were analyzed for the presence of caps.