title: Roles for tumor necrosis factor alpha and nitric oxide in resistance of rat alveolar macrophages to Legionella pneumophila.
abstract: Legionella pneumophila is an intracellular parasite of alveolar macrophages, and recovery from legionellosis is associated with activation of alveolar macrophages to resist intracellular bacterial replication. Gamma interferon (IFN-gamma) is known to activate alveolar macrophages to suppress L. pneumophila, but the role of macrophage-derived cytokines in modulating alveolar macrophage resistance is unknown. To test the hypothesis that macrophage-derived mediators contribute to the resistance of alveolar macrophages to L. pneumophila, we incubated adherent rat alveolar macrophages with Escherichia coli lipopolysaccharide (LPS), recombinant tumor necrosis factor alpha (TNF-alpha), recombinant IFN-gamma, neutralizing anti-TNF-alpha, and/or N(G)-monomethyl-L-arginine (L-NMMA) for 6 h before challenge with L. pneumophila. Monolayers were sonically disrupted and quantitatively cultured on successive days. We also measured bioactive TNF-alpha release by infected macrophages in the presence or absence of IFN-gamma. We found that pretreatment of alveolar macrophages with LPS or, to a lesser degree, TNF-alpha, significantly inhibited intracellular replication of L. pneumophila. Both LPS and TNF-alpha acted synergistically with IFN-gamma at less than the maximally activating concentration to suppress L. pneumophila growth. The independent and coactivating effects of LPS were blocked by anti-TNF-alpha. Killing of L. pneumophila by IFN-gamma at the maximally activating concentration was inhibited by anti-TNF-alpha. The synergistic effects of TNF-alpha. or LPS in combination with IFN-gamma were inhibited by L-NMMA. Infected alveolar macrophages secreted TNF-alpha in proportion to the bacterial inoculum, and secretion of TNF-alpha was potentiated by cocultivation with IFN-gamma. These data indicate that secretion of TNF-alpha is an important autocrine defense mechanism of alveolar macrophages, serving to potentiate the activating effects of IFN-gamma through costimulation of nitric oxide synthesis.
authors: Medical Research Service, Veterans Affairs Medical Center, Seattle, Washington 98108, USA.
authors: S J
authors: SJ
authors: Skerrett
authors: T R
authors: TR
authors: Martin
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D015169:Colony Count, Microbial; D004731:Endotoxins / Q000494:pharmacology; D007113:Immunity, Innate; D007371:Interferon-gamma / Q000494:pharmacology; D016952:Legionella pneumophila / Q000187:drug effects / Q000254:growth & development; D007877:Legionnaires' Disease / Q000276:immunology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000276:immunology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013237:Stereoisomerism; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism*; D019323:omega-N-Methylarginine
chemical_list: D004731:Endotoxins; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D007371:Interferon-gamma; D001120:Arginine