Alveolar macrophages autoregulate IL-1 and IL-6 production by endogenous nitric oxide

The effect of nitric oxide on the lipopolysaccharide (LPS)-induced cytokine production by alveolar macrophages was studied. When alveolar macrophages were cultured, substantial amounts of interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), and nitric oxide are produced upon stimulation with LPS. Inhibition of the nitric oxide production by the L-arginine analogue N-G-monomethyl-L-arginine (NMMA), resulted in an increase of IL-1 beta and IL-6, whereas the TNF-alpha concentrations remained unchanged, suggesting specific inhibitory effects of nitric oxide on the LPS-stimulated cytokine production by alveolar macrophages. The observed cytokine-modulating properties of nitric oxide did not result from cytotoxic actions of the oxidation of L-arginine on macrophages, since nitric oxide synthesis did not affect the viability of the alveolar macrophages. Conversely the nitric oxide donor S-nitroso-N-acetyl-D, L-penicillamine (SNAP) induced dose-dependent inhibition of IL-1 production in LPS-stimulated alveolar macrophages in which endogenous nitric oxide production was blocked. The results indicate that nitric oxide can affect the LPS-induced IL-1 beta and IL-6 secretion by alveolar macrophages in an autoregulatory way and are discussed in view of the important physiologic consequences this autoregulation by nitric oxide may have.