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Curr Top Microbiol Immunol. 2016;397:161-81. doi: 10.1007/978-3-319-41171-2_8.

Inflammasome Recognition and Regulation of the Legionella Flagellum.

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Max von Pettenkofer Institute, Ludwig-Maximilians University, Pettenkoferstraße 9a, 80336, Munich, Germany.
Institute of Medical Microbiology, University of Zürich, Gloriastrasse 30/32, 8006, Zürich, Switzerland.
Institute of Medical Microbiology, University of Zürich, Gloriastrasse 30/32, 8006, Zürich, Switzerland.


The Gram-negative bacterium Legionella pneumophila colonizes extracellular environmental niches and infects free-living protozoa. Upon inhalation into the human lung, the opportunistic pathogen grows in macrophages and causes a fulminant pneumonia termed Legionnaires' disease. L. pneumophila employs a biphasic life cycle, comprising a replicative, non-virulent, and a stationary, virulent form. In the latter phase, the pathogen produces a plethora of so-called effector proteins, which are injected into host cells, where they subvert pivotal processes and promote the formation of a distinct membrane-bound compartment, the Legionella-containing vacuole. In the stationary phase, the bacteria also produce a single monopolar flagellum and become motile. L. pneumophila flagellin is recognized by and triggers the host's NAIP5 (Birc1e)/NLRC4 (Ipaf) inflammasome, which leads to caspase-1 activation, pore formation, and pyroptosis. The production of L. pneumophila flagellin and pathogen-host interactions are controlled by a complex stationary phase regulatory network, detecting nutrient availability as well as the Legionella quorum sensing (Lqs) signaling compound LAI-1 (3-hydroxypentadecane-4-one). Thus, the small molecule LAI-1 coordinates L. pneumophila flagellin production and motility, inflammasome activation, and virulence.


Amoeba; Autoinducer; Dictyostelium; Effector protein; Flagellin; Macrophage; NAIP5/NLRC4 inflammasome; Pathogen vacuole; Phosphoinositide; Quorum sensing; Small GTPase; Type IV secretion

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