The Gram-negative facultative intracellular rod Burkholderia pseudomallei causes melioidosis, an infectious disease with a wide range of clinical presentations. Among the observed visceral abscesses, the liver is commonly affected. However, neither this organotropism of B. pseudomallei nor local hepatic defense mechanisms have been thoroughly investigated so far. Own previous studies using electron microscopy of the murine liver after systemic infection of mice indicated that hepatocytes might be capable of killing B. pseudomallei. Therefore, the aim of this study was to further elucidate the interaction of B. pseudomallei with these cells and to analyze the role of hepatocytes in anti-B. pseudomallei host defense. In vitro studies using the human hepatocyte cell line HepG2 revealed that B. pseudomallei can invade these cells. Subsequently, B. pseudomallei is able to escape from the vacuole, to replicate within the cytosol of HepG2 cells involving its type 3 and type 6 secretion systems, and to induce actin tail formation. Furthermore, stimulation of HepG2 cells showed that IFNγ can restrict growth of B. pseudomallei in the early and late phase of infection whereas the combination of IFNγ, IL-1β, and TNFα is required for the maximal antibacterial activity. This anti-B. pseudomallei defense of HepG2 cells did not seem to be mediated by inducible nitric oxide synthase-derived nitric oxide or NADPH oxidase-derived superoxide. In summary, this is the first study describing B. pseudomallei intracellular life cycle characteristics in hepatocytes and showing that IFNγ-mediated, but nitric oxide- and reactive oxygen species-independent, effector mechanisms are important in anti-B. pseudomallei host defense of hepatocytes.
Keywords: Burkholderia, cytoskeleton, hepatocytes, interferon γ, iNOS, NADPH oxidase, secretion system
Citation: Bast A, Schmidt IHE, Brauner P, Brix B Breitbach K and Steinmetz I (2012) Defense Mechanisms of Hepatocytes Against Burkholderia Pseudomallei. Front. Microbio. 2:277. doi: 10.3389/fmicb.2011.00277
Received: 26 July 2011;
Accepted: 24 December 2011;
Published online: 10 January 2012.
Edited by:Alfredo G. Torres, University of Texas Medical Branch, USA
Reviewed by:Jose A. Bengoechea, Fundacion Caubet – CIMERA Illes Balears, Spain
Copyright: © 2012 Bast, Schmidt, Brauner, Brix, Breitbach and Steinmetz. This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.
*Correspondence: Ivo Steinmetz, Friedrich Loeffler Institut für Medizinische Mikrobiologie, Universitätsmedizin Greifswald KdöR, Martin-Luther-Str. 6, 17475 Greifswald, Germany. e-mail: firstname.lastname@example.org