The roles of Nramp1 and Tnfa genes in nitric oxide production and their effect on the growth of Salmonella typhimurium in macrophages from Nramp1 congenic and tumor necrosis factor-alpha(-/-) mice

The macrophages from Nramp1 congenic mice and tumor necrosis factor (TNF)-a lpha (-/-) mice were used to examine the functions of Nramp1 and Tnfa genes in nitric oxide (NO) production and Salmonella typhimurium infection. It w as confirmed that the level of inducible NO synthase (iNOS)-mediated NO pro duction in Nramp1(r) peritoneal macrophages was generally higher than that of Nramp1(s) macrophages after stimulation by interferon-gamma (IFN-gamma), lipopolysaccharide (LPS), and tumor necrosis factor-alpha (TNF-LU) alone o r in combination, Nramp1 mRNA expression in both Nramp1 congenic macrophage s was constitutive notwithstanding cytokine stimulation. During infection w ith S. typhimurium strain 6203, Nramp1(r) macrophages produced a lower amou nt of NO because of an initial strong reaction and unsustained iNOS gene ex pression as compared with Nramp1(s) macrophages. An inhibitory effect of th e Nramp1(r) gene on bacterial replication was also observed during the earl y stage of S. typhimurium infection, whereas the effect of TNF-alpha occurr ed later. NO production and iNOS expression in TNF-alpha (-/-) macrophages were not detected from the start of the bacterial infection or at 24 h afte r infection. We also observed that S. typhimurium strain 6203 grew more pro foundly without TNF-alpha, especially in Nramp1(s) macrophages, These data, therefore, demonstrate that there is cooperation of the Nramp1 and Tnfa ge nes in NO production and a growth inhibitory effect in response to S. typhi murium infection.