Fas-induced apoptosis of 3DO cells. Ninety-six–well plates were coated with an antibody to hamster IgG (5 μg/well) with or without an antibody to CD2 (5 μg/well). Cells were incubated for 30 minutes with medium alone or medium containing anti-Fas MoAb (10 μg/mL). Apoptosis was evaluated by flow cytometric analysis of PI-stained nuclei after 20 hours of culture. The percentage of apoptotic nuclei is indicated in each histogram. PI fluorescence versus number of nuclei is shown.