Effects of IL-10 and IL-4 on neutrophil-derived COX activity. Human neutrophils (1 × 10⁶ cells) were cultured with or without 10 ng/mL of IL-10 or IL-4 in the presence or absence of LPS (100 ng/mL). After 18 hours, the culture medium was removed, and then fresh medium containing 30 μmol/L AA was added on top of the cell layer. After incubation for 10 minutes, the culture medium was assayed for PGE₂ by RIA. Results are expressed as a percentage of COX activity of unstimulated neutrophils. Similar results were obtained in two separate experiments.