Interleukin-1 receptor antagonist protein inhibits interleukin-8 expression in lipopolysaccharide-stimulated human whole blood.

Interleukin-8 (IL-8) is a neutrophil and lymphocyte chemoattractant and activator that may play an important role in mediating events at sites of inflammation. IL-8 is produced by many cell types in response to a variety of inducers, including interleukin-1 (IL-1). Studies were conducted to address the question of whether an inhibitor of IL-1 action, IL-1 receptor antagonist protein (IRAP), would suppress IL-8 production. Lipopolysaccharide (LPS)-stimulated human whole blood was used as an ex vivo model of local cytokine production. Preliminary time course studies showed that plasma IL-1 beta levels were fully induced by 6 hours (approximately 15 ng/ml) and persisted at this level over 24 hours. IL-8 production, in contrast, reached a plateau between 6 to 12 hours (5 ng/ml) and then increased rapidly to 17 ng/ml at 24 hours. Addition of IRAP was found to dose-dependently inhibit IL-8 expression at the levels of both protein and mRNA. A 50% reduction in IL-8 protein release occurred at an IRAP dose of 8 micrograms/ml (5 x 10(-7) mol/l) at 24 hours. A 2 hour delay in the addition of IRAP relative to LPS still permitted optimal reduction in IL-8 release, whereas delays of 4-8 hours reduced or eliminated the inhibitory effect. IRAP was found to have no effect on the LPS-stimulated production of IL-1 alpha or IL-1 beta. In addition, experiments performed with isolated peripheral blood cells demonstrated that, whereas monocytes were the major producers of IL-8, IRAP was equally effective in reducing IL-8 production in neutrophil and mononuclear cell suspensions. These studies further document the role of IL-1 in inducing the production of IL-8 and indicate that the ability of IRAP to suppress IL-8 expression may be an important mechanism of the anti-inflammatory properties of this molecule.