Augmentation of Nitric Oxide Production by Gamma Interferon in a Mouse Vascular Endothelial Cell Line and Its Modulation by Tumor Necrosis Factor Alpha and Lipopolysaccharide

The effect of gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and lipopolysaccharide (LPS) on nitric oxide (NO) production in the mouse vascular aortic endothelial cell line END-D was examined. LPS, TNF-alpha, and a low concentration of IFN-gamma inhibited NO production in END-D cells, while a high concentration of IFN-gamma definitely enhanced it. The NO production induced by a high concentration of IFN-gamma was further augmented by using IFN-gamma in combination with LPS or TNF-alpha. In sequential incubations of LPS and IFN-gamma, the enhancement of NO production required prior treatment with IFN-gamma. Stimulation of END-D cells with a high concentration of IFN-gamma led to the expression of inducible NO synthase (iNOS). The augmentation of NO production by IFN-gamma alone or in combination with LPS or TNF-alpha was completely blocked by several inhibitors of iNOS. It was strongly suggested that a high concentration of IFN-gamma itself enhanced NO production in END-D cells through inducing the expression of iNOS. LPS and TNF-alpha exclusively modulated the activity of iNOS once its expression was triggered by IFN-gamma. On the other hand, a low concentration of IFN-gamma, LPS, and TNF-alpha reduced NO production through down-regulating constitutive NOS (cNOS). The differential regulation of cNOS- and iNOS-mediated NO production by IFN-gamma, TNF-alpha, and LPS is discussed.