Anti-cytokine therapy for acute and chronic inflammatory diseases has entered clinical medicine. The main targets for anti-cytokine-based therapies are presently tumor necrosis factor (TNF) and interleukin-1 (IL-1), pleiotropic, proinflammatory cytokines. IL-1b is synthesized as a precursor requiring a protease called IL-1b converting enzyme (ICE, caspase-1) for cleavage and secretion of active IL-1b. A relatively new cytokine, IL-18, also uses ICE for cleavage and secretion to an active cytokine. IL-18 is the primary objective for the present study. Specific inhibitors of ICE reduce the release and hence the biological activity of both IL- 1b and IL-18. Mature IL-18 is structurally similar to mature IL-1b. Initially reported as a costimulant of interferon-g (IFNg) production in mice during endotoxemia, our studies demonstrate that IL-18 has broad biological effects similar to those of IL-1b such as inducing the synthesis of other pro-inflammatory cytokines such as the family of chemokines and activation of neutrophils with upregulation of endothelial adhesion molecules. Little is known about the production and biological properties of IL-18 in acute lung injury (ALI) in humans and in murine models of acute lung injury. The current proposal focuses on the nature of the IL-18 production from neutrophils and activation of neutrophils in the context of ALI. We have isolated and cloned a human IL-18 binding protein which specifically neutralizes the biological activity of IL- 18 (IL-18 binding protein, IL-18BP) and likely presents the naturally occurring inhibitor of IL-18. We propose to examine the production of IL-18 and IL-18BP in human neutrophils. The ability of IL-18 to prime neutrophils for generation of superoxide will be used as an indicator of IL-18- mediated neutrophil activation and tissue damage. The ability of IL-18BP to block activation of superoxide production by fMLP will test the role of endogenous, neutrophil-derived IL-18 to functionally affect the same cell that produces the cytokine. Using mice overexpressing the IL- 18BP, we will challenge mice in model of LPS and hemorrhage-induced ALI. Neutralizing antibodies to IL-18 will also be used to reveal the role of endogenous IL-18 in acute lung injury in mice. Exogenous IL-18 will be given parenterally as well as by inhalation. Determinations of IL- 18 and IL-18BP levels will be correlated with disease severity in patients with ALI and correlated with ex vivo responses to LPS challenge. In these studies, we propose to examine the role of this cytokine in acute inflammatory lung disease. These studies will broaden the present therapeutic intervention in ALI.
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