Previously, we have found that a prior burn insult induces lethal acute lung injury (ALI) and overproduction of proinflammatory cytokines after LPS challenge in mice. The current study was aimed to determine the role of IL-18 in burn-induced LPS hypersensitivity. Except sham group, mice were subjected to a 15% total body surface area full-thickness burn and either untreated or treated with IL-18 alone, IL-18 + anti-IL-10 antibody or IL-18 + isotype immunoglobulin G. LPS was intravenously administered to all mice on the 11th day, and the mice were killed at the indicated time point, or survival was examined. We additionally examined cytokine production by splenic cells in vitro for the elucidation of immunologic mechanisms. Unexpectedly, the liver IL-18 decreased transiently after burn injury, and in vivo IL-18 supplementation improved survival and ameliorated ALI, as well as reducing the lung contents of all cytokines examined, except IL-10. Neutralization of IL-10 cancelled the protective effect of IL-18. In splenic macrophages obtained from burned mice, the production of macrophage inflammatory protein 2 (MIP-2), TNF-α, and IL-10 was augmented, whereas in vivo IL-18 supplementation decreased MIP-2 production, but increased IL-10 production. Furthermore, a physiological concentration of IL-18 directly attenuated MIP-2 production by splenic cells in vitro. Burn injury induces LPS hypersensitivity through augmented production of proinflammatory cytokines by systemic macrophages. IL-18 supplementation is protective for LPS-induced lethal ALI through the direct anti-inflammatory effect on macrophages as well as by in vivo acceleration of IL-10 production, and could thus be an effective prophylactic strategy against septic complications in critically ill patients.
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