Role of Interleukin-18 (IL-18) during Lethal Shock: Decreased Lipopolysaccharide Sensitivity but Normal Superantigen Reaction in IL-18-Deficient Mice

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Abstract
Lethal shock can be associated with excessive secretion of cytokines such as tumor necrosis factor (TNF) and gamma interferon (IFN-γ). IFN-γ mediates macrophage activation and appears to be controlled by interleukin (IL)-12 and IL-18. To investigate the role of IL-18 in vivo, we generated IL-18-deficient mice by gene targeting. IL-18−/−mice showed decreased sensitivity towards lipopolysaccharide (LPS)-induced shock. LPS-induced IFN-γ production was abrogated, yet induction of IL-12 and TNF was not affected. Both wild-type and IL-18-deficient mice succumbed to LPS-induced lethal shock after sensitization withd-galactosamine. However, in marked contrast to LPS, the bacterial superantigenStaphylococcus aureusenterotoxin B (SEB) induced comparable serum levels of IFN-γ in IL-18+/+and IL-18−/−mice, accompanied by an upregulation of cell surface markers CD14, CD122 (IL-2Rβ), and CD132 (IL-2Rγ) on peritoneal macrophages. Moreover, SEB injection rendered IL-18-deficient mice sensitive for subsequent challenge with LPS. The degree of sensitization was comparable to that in wild-type controls with respect to lethality. However, LPS-induced TNF levels in serum were significantly reduced in SEB-sensitized IL-18-deficient mice. These results imply that IL-18 plays an important role in induction of IFN-γ and lethality in response to LPS.

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