Inhibitory activity of constitutive nitric oxide on the expression of alpha/beta interferon genes in murine peritoneal macrophages

We investigated the role of the constitutive nitric oxide (NO) in the expre ssion of interferon (IFN) genes in mouse peritoneal macrophages (PM). The t reatment of PM with carginine-N-G-amine (AA), a potent inhibitor of NO-prod ucing enzymes, resulted in a marked accumulation of IFN-alpha 4 mRNA and, t o a minor extent, of IFN-beta mRNA. In contrast, the expression of IFN-gamm a mRNA, as well as tumor necrosis factor alpha and interleukin-6 mRNA, was not affected. Furthermore, a remarkable increase in the expression of the I FN regulating factor 1 (IRF-1), but not of IRF-2, mRNA was detected in AA-t reated PM. To investigate whether the AA-induced activation of the IFN syst em correlates with the production and antiviral activity of IFN, the extent of encephalomyocarditis virus (EMCV) replication was monitored in AA-treat ed PM with respect to control cultures. AA treatment strongly inhibited, in a dose-dependent manner, EMCV yields in PM. Likewise, similar results were obtained by the addition of the NO-scavenger carboxyphenyl-tetramethylimid azoline-oxyl- oxide. In addition, inhibition of NO synthesis by N-G-mono-me thyl-L-arginine in PM strongly decreased virus replication in coculture of PM and EMCV-infected L929 cells, whereas no antiviral effect was observed i n L929 cells alone. Moreover, the AA-mediated antiviral activity was abroga ted in the presence of antibody to IFN-alpha/beta, whereas antibody to IFN- gamma was completely ineffective. Taken together, these results indicate th at low levels of NO, constitutively released by resting PM, negatively regu late the expression and activity of IFN-alpha/beta in PM. We suggest that N O acts as a homeostatic agent in the regulation of IFN pathway expression i n macrophages.