Effect of TNF-α on neutrophil morphology and propidium iodide (PI) staining. Human neutrophils were incubated in the presence (A and B, righthand panels) or absence (A and B, lefthand panels) of 12.5 ng/mL TNF-α as detailed in the legend to Fig 1. (A) Cytocentrifuge preparations were prepared after 6 hours and cells fixed, stained, and examined under 100× objective oil immersion light microscopy. Cells with classical apoptotic morphology are arrowed. (B) After 6 or 20 hours in culture cells were resuspended in ice-cold 70% ethanol, washed in PBS, and incubated with PI in the presence of RNAase before analysis using an EPICS Profile II. Mean fluorescence values are shown for a minimum of 5,000 cells for each condition and are representative of six to nine determinations in three separate experiments.