BACTERIAL INDUCTION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN CULTURED HUMAN INTESTINAL EPITHELIAL-CELLS

Background & Aims: Enterocytes play a major role in the mucosa as a so urce of proinflammatory cytokines and cytotoxins, We tested the hypoth esis that bacteria induce expression of the inducible nitric oxide syn thase (iNOS) in cultured human enterocytes. Methods: DLD-1 and Caco-2B Be cell monolayers exposed to Salmonella dublin were analyzed for iNOS up-regulation and nitric oxide production (NOx) in the presence of va rious proinflammatory cytokines, Results: S. dublin augmented NOx in i nterferon gamma (IFN-gamma)-primed cells but had no independent effect on iNOS expression. S. dublin-induced NOx was not mediated by endotox in and was augmented by an enteroinvasive phenotype. In DLD-1 cells, S . dublin-mediated NOx was blocked by inhibitors of nuclear factor kapp a B (NF-kappa B) and tyrosine kinase activation and was steroid resist ant, Cis-acting elements in the human iNOS promoter responsive to endo toxin and S. dublin stimulation of IFN-gamma-treated DLD-1 cells were identified between 10.9 and 8.7 kilobases upstream of the transcriptio n initiation site, Conclusions: S. dublin alters the regulation of iNO S messenger RNA in IFN-gamma-treated intestinal epithelial cells via a steroid-resistant pathway involving NF-kappa B and tyrosine kinase ac tivity, Because bacterial interaction with cytokine-primed epithelial cells induces the synthesis of NO, an endogenous antimicrobial agent, these findings may have implications for the regulation of mucosal imm unity.