Nitric oxide reduces bacterial superantigen-immune cell activation and consequent epithelial abnormalities

Inhibition of the inducible form of nitric oxide (NO) synthase prolonged the murine enteropathy evoked by the bacterial superantigen, Staphylococcus aureus enterotoxin B (SEB). We examined the ability of NO to alleviate SEB-induced epithelial dysfunction and immune cell activation. Human peripheral blood mononuclear cells (PBMC) were activated by SEB for 24 h +/- the NO donors, S-nitroso-N-acetylpenicillamine and spermine-NONOate. The conditioned medium (CM) was collected and applied to T84 epithelial monolayers, and permeability [i.e., transepithelial resistance (TER)] and stimulated ion transport (i.e., short-circuit current responses to carbachol and forskolin) were assessed 24 h later. Exposure to CM led to an approximately 40% drop in TER and hyporesponsiveness to both secretagogues. CM made in the presence of NO donors (10(-4) M) had no significant effect on epithelial barrier or ion transport parameters. NO donors alone had no effect on naive epithelia, and addition of the NO donors to previously made CM did not affect the ability of this CM to alter epithelial function. Moreover, the NO donors dose-dependently reduced SEB-evoked PBMC proliferation and cytokine production (i.e., interferon-gamma, tumor necrosis factor alpha) but did not affect viability. These findings suggest a beneficial role for NO in inflammation by reducing immune cell activation and thus ameliorating consequent physiological abnormalities, in this instance, perturbed epithelial permeability and active ion transport.