Nitric oxide inhibits Coxiella burnetii replication and parasitophorous vacuole maturation.
Nitric oxide is a recognized cytotoxic effector against facultative and obligate intracellular bacteria. This study examined the effect of nitric oxide produced by inducible nitric oxide synthase (iNOS) up-regulated in response to cytokine stimulation, or by a synthetic nitric oxide donor, on replication of obligately intracellular Coxiella burnetii in murine L-929 cells. Immunoblotting and nitrite assays revealed that C. burnetii infection of L-929 cells augments expression of iNOS up-regulated in response to gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). Infection in the absence of cytokine stimulation did not result in demonstrable up-regulation of iNOS expression or in increased nitrite production. Nitrite production by cytokine-treated cells was significantly inhibited by the iNOS inhibitor S-methylisothiourea (SMT). Treatment of infected cells with IFN-gamma and TNF-alpha or the synthetic nitric oxide donor 2,2'-(hydroxynitrosohydrazino)bis-ethanamine (DETA/NONOate) had a bacteriostatic effect on C. burnetii replication. Inhibition of replication was reversed upon addition of SMT to the culture medium of cytokine-treated cells. Microscopic analysis of infected cells revealed that nitric oxide (either cytokine induced or donor derived) inhibited formation of the mature (large) parasitophorous vacuole that is characteristic of C. burnetii infection of host cells. Instead, exposure of infected cells to nitric oxide resulted in the formation of multiple small, acidic vacuoles usually containing one C. burnetii cell. Removal of nitrosative stress resulted in the coalescence of small vacuoles to form a large vacuole harboring multiple C. burnetii cells. These experiments demonstrate that nitric oxide reversibly inhibits replication of C. burnetii and formation of the parasitophorous vacuole.
Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071-3944, USA.
Dale
D
Howe
Lorraine F
LF
Barrows
Nicole M
NM
Lindstrom
Robert A
RA
Heinzen
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D016997:Coxiella burnetii / Q000187:drug effects* / Q000254:growth & development* / Q000472:pathogenicity; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D051379:Mice; D009569:Nitric Oxide / Q000096:biosynthesis / Q000494:pharmacology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D011778:Q Fever / Q000209:etiology / Q000276:immunology / Q000378:metabolism; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014617:Vacuoles / Q000187:drug effects / Q000382:microbiology
D020030:Nitric Oxide Donors; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse