IL-25 inhibits the expression of TNF-α and IL-6 induced by LPS and PGN in CD11c⁺ cells isolated from the spleen of Balb/c mice. IL-25 inhibited the expression of TNF-α (A) and IL-6 (B). CD11c⁺ cells were preincubated with medium (no IL-25) or IL-25 for 30 minutes, then either left unstimulated (M = medium) or stimulated with LPS or PGN for a further 6 hours. RNA was then extracted and amplified by real-time PCR. Levels are normalized to β-actin and indicate the mean (± SD) of all experiments. *P = .01. IL-25–treated mice have decreased serum levels of IL-12p70 (C), TNF-α (D), and IL-6 (E) after systemic administration of LPS or PGN. Groups of 5 Balb/c mice were injected intraperitoneally with PBS (no IL-25) or PBS containing murine IL-25 (10 μg/mouse). One hour later animals received PBS (naive), LPS (300 μg/mouse), or PGN (300 μg/mouse). Serum samples were collected at 5 hours and analyzed for cytokine levels by ELISA. Data indicate the mean (± SD) of all experiments. *P = .03; **P < .02. (F) IL-25 protects mice from death. Mice were injected with or without IL-25 and then treated with LPS as indicated above. Similar results were obtained in 3 separate experiments. *P = .02; **P = .001.