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Francisella tularensis LVS initially activates but subsequently down-regulates intracellular signaling and cytokine secretion in mouse monocytic and human peripheral blood mononuclear cells.
Umeå University, Faculty of Medicine, Clinical Microbiology, Clinical Bacteriology.
Umeå University, Faculty of Medicine, Clinical Microbiology, Clinical Bacteriology.
Umeå University, Faculty of Medicine, Clinical Microbiology, Clinical Bacteriology.
2005 (English)In: Microbial Pathogenesis, ISSN 0882-4010, Vol. 38, no 5-6, 239-247 p.Article in journal (Refereed) Published
Abstract [en]

Monocytic cells constitute an important defense mechanism against invading pathogens by recognizing conserved pathogens components. The recognition leads to activation of intracellular pathways involving nuclear factor kappa B (NF-kappaB) and mitogen-activated protein kinases (MAPK), such as the c-Jun NH2-terminal kinase (JNK), and p38. We show that in vitro infection with Francisella tularensis results in activation of NF-kappaB, phosphorylation of p38 and c-Jun, and secretion of TNF-alpha in adherent mouse peritoneal cells, in the mouse macrophage-like cell line J774A.1, in the human macrophage cell line THP-1, and in human peripheral blood monocytic cells. This occurred after infection with the human live vaccine strain, F. tularensis LVS or a mutant strain denoted deltaiglC, which lacks expression of a 23-kDa protein, or after addition of killed F. tularensis LVS. Addition of purified F. tularensis LPS resulted in no discernible effects on the cells. When the effects were followed up to 5 h, activation persisted in cultures with killed bacteria or infected with the deltaiglC strain. In contrast, the signal transduction activation and secretion of TNF-alpha were down-regulated within the 5h period in mouse peritoneal cells, J774 cells or human peripheral blood mononuclear cells infected with F. tularensis LVS. Together, the results suggest that infection with live F. tularensis LVS bacteria leads to a rapid induction of a proinflammatory response in mouse and human cells but after internalization of bacteria, this response is completely or partly down-regulated in most cell types. This down-regulation does not occur when cells are infected with the mutant deltaiglC.

Place, publisher, year, edition, pages
2005. Vol. 38, no 5-6, 239-247 p.
Identifiers
URN: urn:nbn:se:umu:diva-4612DOI: 10.1016/j.micpath.2005.02.003PubMedID: 15925273OAI: oai:DiVA.org:umu-4612DiVA: diva2:143782
Available from: 2005-05-31 Created: 2005-05-31 Last updated: 2009-11-30Bibliographically approved
In thesis
1. Effects of Francisella tularensis infection on macrophage intracellular signaling
Open this publication in new window or tab >>Effects of Francisella tularensis infection on macrophage intracellular signaling
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Microbes contain a number of structural components, also known as pathogen associated molecular patterns (PAMP), which can be recognized by the host defense system. The PAMP serve as ligands for Toll-like receptors (TLR) expressed on phagocytic cells. Binding of PAMP to TLR leads to activation of a number of intracellular transduction pathways including NF-�B and mitogen-activated protein kinase pathways (MAPK). Activation of those pathways in turn leads to activation of proinflammatory immune responses and antimicrobial defense mechanisms. In this study we show that the intracellular pathogen F. tularensis LVS can induce a proinflammatory response during internalization in both human and mouse macrophages. However, after internalization, F. tularensis LVS effectively blocks all these pathways resulting in no secretion of proinflammatory cytokines in mouse macrophages. In human macrophages, a downregulation was observed, however, there was not a complete block as in the murine cells. Furthermore, the infected cells do not become activated by stimulation with TLR agonists such as Escherichia coli LPS or bacterial lipoprotein. This phenomenon is observed only when the cells were infected with the LVS strain, but not with killed bacteria or specific mutants such as iglC, or mglA mutants, suggesting that not only their presence but also rapid regulation of the Igl proteins are needed. Thus, Igl/Mgl system plays a very important role in mediating these inhibitory effects. To further investigate the role of the Igl/Mgl proteins in the virulence of F. tularensis, we established a novel model for tularemia, infection of Drosophila melanogaster. Using the fly model as a way to mimic the F. tularensis infection in arthropod vectors, which are important for its life cycle, we observed that bacterial mutants in each of the IglB, IglC, IglD, or MglA proteins all showed less efficient killing of the flies than did the parental LVS strain. Nitric oxide, superoxide, and the reaction product of the two mediators, peroxynitrite, all are important for regulation of eukaryotic cell signaling and effectuating bactericidal mechanisms. To this end, we investigated the role of these mediators for the F. tularensismediated TLR-signaling inhibition. We observed that whereas peroxynitrite had little effect on the inhibition, addition of SNAP, a donor of nitric oxide, partially restored the ability of the cells to respond to LPS stimulation and secrete proinflammatory cytokine such as TNF-�. However, since FeTTPS reversed the SNAP-mediated effect, the results indicate that NO forms peroxynitrite intracellular and that the latter molecule is the effector. Together these results indicate that F. tularensis contains PAMP that can activate proinflammatory immune response while the bacteria are located outside of phagocytic cell and during internalization, however, the intracellular bacteria have means to inhibit the activation of anti-bacterial systems of macrophages and block inflammatory responses completely in mouse cells and partially in human cells. This suppression may lead to disruption of synthesis of bactericidal effector molecules, allowing F. tularensis to survive and rapidly proliferate inside phagocytic cells. The ability to suppress the inflammatory responses is dependent on expression of the Igl/Mgl proteins. The Igl/Mgl system is also critical for the ability of F. tularensis to replicate in mammalian cells and in D. melanogaster.

Place, publisher, year, edition, pages
Umeå: Klinisk mikrobiologi, 2005. 55 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 960
Research subject
Clinical Bacteriology
Identifiers
urn:nbn:se:umu:diva-547 (URN)91-7305-898-3 (ISBN)
Public defence
2005-05-31, Sal E04, NUS, By 6E, Umeå, 09:00 (English)
Opponent
Available from: 2005-05-31 Created: 2005-05-31 Last updated: 2012-06-28Bibliographically approved

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