Constitutive PMN apoptosis in the presence of NBD or control peptide. Cells were incubated with buffer control (cells), TAT-NBD (N), or mutant control peptide (c). After 20 hours, cells were harvested and the percentage of apoptotic PMNs was assayed by flow cytometry using (A) propidium iodide (PI; n = 4) or (B) annexin V staining (n = 4). **P < .01 when compared with untreated cells. The values represent mean ± SEM. (C) A typical experiment with both assays performed in parallel is depicted using a peptide concentration at 100 μM. The data indicate that TAT-NBD (NBD) accelerated apoptosis in a dose-dependent fashion over a range of 1 to 200 μM. In contrast, no effect was seen in the presence of a mutant control peptide (MUT). The percentage of apoptotic cells is indicated by the marker.