The effect of IL-4 on LTA₄ hydrolase activity.

(A) Time-course study. After PMNs were incubated with 10 ng/mL of IL-4 for various periods of time, the cell lysates were prepared and incubated with LTA₄ at 37°C for 5 minutes. The supernatant was recovered, and the concentration of LTB₄was measured by HPLC as described in “Materials and methods.” (B) Dose-response study. After PMNs were incubated with various concentrations of IL-4 (0.1, 1, 10, 100 ng/mL) for 6 hours, the cell lysates were incubated with LTA₄ at 37°C for 5 minutes. The supernatant was recovered, and the concentration of LTB₄ was measured by HPLC. Data represent mean ± SEM (n = 4). *P < .05 versus control.