Induction of apoptosis by FcαRI targeting in human monocytic cell lines. (A) Induction of apoptosis in MonoMac6 or U937 cells after 24 hours of treatment with 20 μg/mL anti-FcαRI (A77) Fab or control (320) Fab. Cells were stained with PI and analyzed for the appearance of hypoploid nuclei as described in “Materials and methods.” Numbers indicate the percentage of cells with hypoploid nuclei. Values indicate the percentage of double-positive cells and are means ± SD of at least 3 separate experiments performed in duplicate. *P < .01. (B) Analysis of the “cleaved” (activated) form of caspase-3 following anti-FcαRI Fab treatment. The MonoMac6 or U937 cells were treated with 20 μg/mL A77 or control (320) Fab for indicated times. Cells were then lysed, separated by SDS-PAGE, and transferred to PVDF membranes before immunoblotting with an antibody recognizing the cleaved form of caspase-3. To control for equal loading, blots were stripped and reprobed with antiscramblase (PLSCR) antibody plus goat anti–rabbit Ig-HRP. One representative experiment of 3 is shown.