Effect of neutrophil cell concentration on the early proapoptotic effect of TNF-α. Human neutrophils were incubated at a cell concentration of 2.5 to 15 × 10⁶/mL in the presence (▪) or absence (▧) of TNF-α (12.5 ng/mL) for 6 hours at 37°C. Cytocentrifuge slides were then prepared for morphological assessment of apoptosis. Data represent the mean ± SEM of six observations in two separate experiments.