Evaluation of PMN apoptosis in the presence of cytokine-activated NK-cell supernatant. (A) PMNs were cultured in the absence (Med) or presence (NK + IL-2) of IL-2–activated NK-cell supernatant, and stained with annexin and viaprobe to determine apoptosis. Annexin⁺viaprobe⁻ cells (top left quadrant) were defined as apoptotic and annexin⁻viaprobe⁻ cells (bottom left quadrant) as living. (B) The percentage of apoptotic PMNs was determined at different time points in the absence (Med) or presence (NK + IL-2) of IL-2–activated NK-cell supernatant (n= 1). The data points represent the percentage of apoptotic PMNs when cultured alone or with supernatants from cytokine-activated NK cells. (C) Quantitative representation of the percentage of apoptotic PMNs when cultured alone (Med) or with supernatants from unstimulated (NK sup) or IL-2–activated (NK + IL-2 sup) NK cells for 18-24 hours, from 24 individual experiments totally. (D) PMNs cultured with supernatants from NK cells stimulated with IL-2, IL-21, IL-15, IL-12, IL-18, or a combination of IL-12 plus IL-18 compared with control medium (Med) and PMNs treated with cytokines alone (n= 5). The results are expressed as mean ± SEM. ***P < .001.