EXOGENOUS NITRIC-OXIDE REGULATES IFN-GAMMA PLUS LIPOPOLYSACCARIDE-INDUCED NITRIC-OXIDE SYNTHASE EXPRESSION IN MOUSE MACROPHAGES

This study was performed to determine the effects of nitric oxide (NO) on the expression of inducible NO synthase (iNOS) in mouse macrophage s. We used the NO donor diethylamine dinitric oxide (DEA/NO) and the m ouse macrophage cell line ANA-1 in these experiments. ANA-1 macrophage s did not express iNOS mRNA either constitutively or following exposur e to 100 U/ml IFN-gamma alone, to 10 ng/ml LPS alone, or to 200 mu M D EA/NO alone. Similarly, ANA-1 macrophages did not express detectable l evels of iNOS mRNA following treatment with 100 U/ml IFN-gamma plus 20 0 mu M DEA/NO. However, IFN-gamma (100 U/ml) plus LPS (10 ng/ml) induc ed high levels of iNOS mRNA in ANA-1 macrophages after 6 h. Low concen trations of DEA/NO (approximately 1 to 12 mu M) caused up to a 2.5-fol d augmentation of IFN-gamma plus LPS-induced iNOS mRNA expression. In contrast, 200 mu M DEA/NO suppressed IFN-gamma plus LPS-induced iNOS m RNA expression (60% decrease). The effects of DEA/NO were gene-specifi c because DEA/NO did not affect the IFN-gamma plus LPS-induced express ion of TNF-alpha mRNA. Moreover, the biphasic effects of DEA/NO were s pecifically due to released NO. Diethylamine and nitrite were unable t o regulate IFN-gamma plus LPS-induced gene expression in ANA-1 macroph ages. Time-response experiments suggested that the effects of NO were short-lived and occurred early during the induction of iNOS gene expre ssion. The effects of NO were not limited to iNOS mRNA expression but were apparent at the level of iNOS protein expression and enzymatic ac tivity. Overall, these results suggest that NO has immunoregulatory ef fects and may control the extent and duration of cytokine- and/or endo toxin-induced iNOS expression in macrophages.