| Title | TLR2-Mediated Signaling Requirements for Francisella tularensis LVS Infection of Murine Macrophages. | | Author(s) | Cole LE, Shirey KA, Barry E, Santiago A, Rallabhandi P, Elkins KL, Puche A, Michalek SM, Vogel SN | | Institution | Department of Microbiology and Immunology, Center for Vaccine Development, and Department of Anatomy and Neurobiology, University of Maryland, Baltimore, School of Medicine, Baltimore, MD 21201; Laboratory of Mycobacterial Diseases and Cellular Immunology, Division of Bacterial, Allergenic, and Parasitic Products, CBER/FDA, Bethesda, MD 20852; Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294. | | Source | Infect Immun 2007 May 21. | | Abstract | Francisella tularensis (Ft), an aerobic, non-spore forming, Gram-negative coccobaccillus, is the causative agent of tularemia. We reported previously that Ft Live Vaccine Strain (LVS) elicited strong, dose-dependent NF-kappaB reporter activity in TLR2-expressing HEK293T cells and pro-inflammatory gene expression in primary murine macrophages. Herein, we report that Ft LVS-induced murine macrophage pro-inflammatory cytokine gene and protein expression is overwhelmingly TLR2-dependent as evidenced by the abrogated responses of TLR2(-/-) macrophages. Ft LVS infection also increased expression of TLR2 both in vitro, in mouse macrophages, and in vivo, in livers from Ft LVS-infected mice. Colocalization of intracellular Ft LVS, TLR2, and MyD88 was visualized by confocal microscopy. Signaling was abrogated if the Ft LVS were heat- or formalin-killed or treated with chloramphenicol, indicating that the TLR2 agonist activity is dependent on new bacterial protein synthesis. Ft LVS replicates in macrophages; however, bacterial replication was not required for TLR2 signaling because LVSDeltaguaA, a Ft LVS guanine auxotroph that fails to replicate in the absence of exogenous guanine, activated NF-kappaB in TLR2-transfected HEK293T cells and induced cytokine expression in wild-type macrophages comparably to wild-type (WT) Ft LVS. Collectively, these data indicate that the primary macrophage response to Ft LVS is overwhelmingly TLR2-dependent, requires de novo bacterial protein synthesis, and is independent of intracellular Ft replication. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 17517865 |
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