Interferon-gamma reverses the evasion of Birc1e/Naip5 gene mediated murine macrophage immunity by Legionella pneumophila mutant lacking flagellin

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Abstract

Legionella pneumophila is the etiologic agent of Legionnaires' disease. This bacterium contains a single monopolar flagellum, of which the FlaA subunit is a major protein constituent. The murine macrophage resistance against this bacterium is controlled by the Birc1e/Naip5 gene, which belongs to the NOD family. We evaluated the intracellular growth of the flaA mutant bacteria as well as another aflagellated fliA mutant, within bone marrow-derived macrophages from mice with an intact (C57BL/6, BALB/c) or mutated (A/J) Birc1e/Naip5 gene. The flaA mutant L. pneumophila multiplied within C57BL/6 and BALB/c macrophages while the wild-type strain did not. Cell viability was not impaired until 3 days after infection when the flaA mutant bacteria replicated 102-3-fold in macrophages, implying that L. pneumophila inhibited host cell death during the early phase of intracellular replication. The addition of recombinant interferon-gamma (IFN-γ) to the infected macrophages restricted replication of the flaA mutant within macrophages; these treated cells also showed enhanced nitric oxide production, although inhibition of nitric oxide production did not affect the IFN-γ induced inhibition of Legionella replication. These findings suggested that IFN-γ activated macrophages to restrict the intracellular growth of the L. pneumophila flaA mutant by a NO independent pathway.

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Akamine, M., Higa, F., Haranaga, S., Tateyama, M., Mori, N., Heuner, K., & Fujita, J. (2007). Interferon-gamma reverses the evasion of Birc1e/Naip5 gene mediated murine macrophage immunity by Legionella pneumophila mutant lacking flagellin. Microbiology and Immunology, 51(3), 279–287. https://doi.org/10.1111/j.1348-0421.2007.tb03909.x

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