Production of IL-1Ra by the HepG2 human hepatoma cell line and by human primary hepatocytes. HepG2 cells were cultured in the absence (control) or presence of IL-1β, IL-6, and a combination of IL-1β and IL-6 without (□) or with the addition of 1 ng/mL (▩) or 10 ng/mL (▩) IL-4 (A). Similar experiments were performed with the addition (▩) of 10 ng/mL IL-13 in HepG2 cells (B) and of 10 ng/mL IL-4 in human primary hepatocytes (C). After 18 hours of stimulation, levels of IL-1Ra were measured by ELISA in culture supernatants. Values represent the mean ± SEM of three experiments. ^*P < 0.01 in comparison with cells cultured in the absence of IL-4 or IL-13.