Granulocytes from PNH patients resist apoptosis as compared with normal granulocytes. Freshly purified granulocytes were serum starved and then analyzed for evidence of apoptosis. (A) PNH granulocytes at 12 hours were stained with propidium iodide and analyzed by flow cytometry. The narrow, tall peak on each histogram represents cells with a normal (2n) amount of DNA, whereas the broader peak represents apoptotic cells with a sub-2n amount of DNA. The granulocytes from a PNH patient have less apoptosis (34% sub-2n PI staining) than those from a normal control (58%). (B) Cells at 6 hours were stained with annexin V-FITC and PI to identify apoptotic cells that are positive for annexin binding but exclude PI. The granulocytes from a PNH patient have less apoptosis (26% annexin V-FITC staining) than those from a normal control (59%). (C) Genomic DNA was analyzed for fragmentation. At time zero no laddering was observed, but after 12 hours of serum starvation, DNA from PNH granulocytes had less laddering than the DNA from the granulocytes of a normal control.