Apoptosis of cell lines does not depend on a functioning PIG-A gene sequence or levels of GPI-linked surface expression. Cells were subjected to stimuli and analyzed for apoptosis by PI staining and flow cytometry. All data points were performed in triplicate for each experiment, and the displayed results represent six to eight independent experiments (mean ± 1 SD) for each stimulus. Upper left panel: Control antibody, with minimal apoptosis detected. Lower left panel: Fas antibody, with apoptosis ranging from 37.5% ± 10.1% to 46.8% ± 10.3%. Upper right panel: Serum starvation, with apoptosis ranging from 8.5% ± 2.6% to 22.2% ± 8.0%. Lower right panel: γ-irradiation, with apoptosis ranging from 27.9% ± 7.4% to 48.8% ± 18.8%. There were no statistically significant differences among the various cell lines, according to the presence of a functioning PIG-A gene or surface expression of GPI-linked proteins.