Double-stranded RNA-induced inducible nitric-oxide synthase expression and interleukin-1 release by murine macrophages requires NF-κB activation

The effects of double-stranded RNA (synthetic polyi nosinic-polycytidylic acid; poly(I-C)) on macrophage expression of inducible nitric-oxide synthase (iNOS), production of nitric oxide, and release of interleukin-1 (IL-1) were investigated. Individually, poly(I-C), interferon-gamma (IFN-gamma), and lipopolysaccharide (LPS) stimulate late nitrite production and iNOS expression by RAW 264.7 cells. In combination, the effects of poly(I-C) + IFN-gamma are additive, while poly(I-C) does not further potentiate LPS-induced nitrite production. These re suits suggest that poly(I-C) and LPS may stimulate iNOS expression by similar signaling pathways, which may be independent of pathways activated by IFN-gamma, LPS-induced iNOS expression is associated with the activation of NF-kappa B. We show that inhibition of NF-kappa B by pyrrolidine dithiocarbamate prevents poly(I-C) + IFN-gamma-, poly(I-C) + LPS-, and LPS-induced iNOS expression, nitrite production and I kappa B degradation by RAW 264.7 cells. The effects of poly(I-C) on iNOS expression appear to be cell-type specific. Poly(I-C), alone or in combination with IFN-gamma, does not stimulate, nor does poly(I-C) potentiate, IL-1-induced nitrite production by rat insulinoma RINm5F cells. In addition, we show that the combination of poly(I-C) + IFN-gamma stimulates iNOS expression, nitrite production I kappa B degradation, and the release of IL-1 by primary mouse macrophages, and these effects are prevented by pyrrolidinedithiocarbamate. These findings indicate that double-stranded RNA, in the presence of IFN-gamma, is a potent activator of macrophages, stimulating iNOS expression, nitrite production, and IL-1 release by a mechanism which requires the activation of NF-kappa B.