title: Immunoregulatory role of nitric oxide in Legionella pneumophila-infected macrophages.
abstract: Nitric oxide (NO) is an intercellular messenger molecule produced by a variety of cells, including macrophages. However, the role of NO in infection, especially its immunological role, is poorly understood. In the present study, the role of NO in Legionella pneumophila-infected macrophages was examined. Whereas infection of mouse macrophages in vitro with L. pneumophila did not induce detectable NO, when the macrophages were primed with interferon-gamma (IFN-gamma), the treated macrophages markedly inhibited bacterial replication and produced a large amount of NO. Treatment with NO inhibitors, such as NG-monomethyl-L-arginine (L-MMA) or aminoguanidine, as well as culture in arginine-free medium, significantly inhibited NO production; however, the anti-L. pneumophila activity induced by IFN-gamma was not diminished. Examination of cytokine levels in L. pneumophila-infected macrophages primed with IFN-gamma revealed a moderate increase of interleukin-6 (IL-6) production; however, inhibition of NO by L-MMA markedly increased IL-6 production. Reconstitution of NO in the L. pneumophila-infected macrophages primed with IFN-gamma and treated with L-MMA to inhibit endogenous NO production following addition of sodium nitroprusside reduced IL-6 production to normal levels. The levels of IL-6 mRNA in L-MMA-treated macrophages were the same as in nontreated macrophages, as demonstrated by quantitative RT-PCR. Thus, these results indicate that NO may regulate IL-6 production independently of its role in antimicrobial function in L. pneumophila-infected macrophages and their immunoregulation on IL-6 production may be due to a post-transcriptional mechanism.
authors.affiliation: Department of Medical Microbiology and Immunology, University of South Florida College of Medicine, Tampa 33612, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: T W
authors.initials: TW
authors.lastname: Klein
authors.forename: H
authors.initials: H
authors.lastname: Friedman
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002478:Cells, Cultured; D005260:Female; D006146:Guanidines / Q000494:pharmacology; D007371:Interferon-gamma / Q000494:pharmacology; D015850:Interleukin-6 / Q000096:biosynthesis / Q000235:genetics; D016952:Legionella pneumophila / Q000276:immunology*; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D008805:Mice, Inbred A; D008807:Mice, Inbred BALB C; D009569:Nitric Oxide / Q000096:biosynthesis / Q000276:immunology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000378:metabolism; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D006146:Guanidines; D015850:Interleukin-6; D012333:RNA, Messenger; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; C004479:pimagedine