EXOGENOUS AND ENDOGENOUS TYPE-I INTERFERONS INHIBIT INTERFERON-GAMMA-INDUCED NITRIC-OXIDE PRODUCTION AND NITRIC-OXIDE SYNTHASE EXPRESSION IN MURINE PERITONEAL-MACROPHAGES

We investigated the effect of type I IFNs (IFN-alpha and IFN-beta) on IFN-gamma-induced nitric oxide (NO) production by murine peritoneal ma crophages. It was found that exogenous and also endogenous type I IFNs suppressed IFN-gamma-induced NO production, cytosolic inducible NO sy nthase (iNOS) activity, and iNOS mRNA accumulation in macrophages. Fur thermore, we show here that type I IFNs prevent the NO-mediated deteri oration of mitochondrial respiratory activity in macrophages. These re sults seem to indicate a possible protective role of type I IFNs again st the NO-mediated immunosuppressive and/or cytotoxic effect of macrop hages.