Effects of IL-10 and IL-4 on COX-2–derived PGE₂ (A) and TXB₂ (B) production in neutrophils. Human neutrophils (1 × 10⁶ cells) were treated for 2 hours in the presence of aspirin (500 μmol/L) to inactivate endogenous COX-1, washed three times with PBS, and then cultured for 24 hours with medium, LPS (100 ng/mL), LPS plus IL-4 (10 ng/mL), LPS plus IL-10 (10 ng/mL), or LPS plus NS-398 (1 μmol/L). RIA for PGE₂ (A) and TXB₂ (B) was performed as described in Materials and Methods. Similar results were obtained in two separate experiments.