Antagonistic effects of IL-4 and interferon-gamma (IFN-gamma) on inducible nitric oxide synthase expression in bovine macrophages exposed to gram-positive bacteria.

Cytokine-mediated modulation of nitric oxide (NO) production by bacteria-stimulated bovine macrophages was studied. When Salmonella dublin, as a prototypic gram-negative organism, was used, NO generation was barely enhanced by recombinant bovine and ovine IFN-gamma, but was suppressed by IL-4. Salmonella dublin-induced NO generation was not influenced by a panel of nine other cytokines. The panel included IL-1, tumour necrosis factor (TNF) and IFN-alpha, which are active in a similar mouse macrophage model. The tested cytokines were either homologous or known to interact with bovine cytokine receptors. Recombinant bovine and ovine IFN-gamma were the only cytokines which strongly enhanced NO synthesis by macrophages exposed to the gram-positive organism, Listeria monocytogenes. Listeria-induced NO generation was strongly suppressed by recombinant human and bovine IL-4, but not by IL-10 and transforming-growth-factor-beta. Thus, two cytokines characterizing a Th1 and a Th2 response up- and down-regulate, respectively, bacteria-induced NO generation in bovine macrophages, whereas nine other cytokines had little activity in this regard. This modulation was reflected in changes in the steady state levels of mRNA coding for inducible nitric oxide synthase. Combinations of IFN-gamma and IL-4 suggested that the relative proportion of these cytokines determined whether bacteria-induced NO generation was up- or down-regulated. At saturating IL-4 concentrations, stimulation of bacteria-induced NO generation in macrophages by T cell supernatants was solely dependent on IFN-gamma. This was shown by antibody neutralization experiments and by a close correlation between the capacity of supernatants to stimulate NO generation and the IFN-gamma content, as determined by immunoassay.