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Lipoproteins of Listeria monocytogenes Are Critical for Virulence and TLR2-Mediated Immune Activation¹

Silke Machata^2,*, Svetlin Tchatalbachev^2,3,*, Walid Mohamed^*, Lothar Jänsch, Torsten Hain^* and Trinad Chakraborty^*

^* Institute of Medical Microbiology, Justus-Liebig-University, Giessen, Germany; and Helmholtz Centre for Infection Research, Braunschweig, Germany

Numerous cell surface components of Listeria influence and regulate innate immune recognition and virulence. Here, we demonstrate that lipidation of prelipoproteins in Listeria monocytogenes is required to promote NF-B activation via TLR2. In HeLa cells transiently expressing TLR2, L. monocytogenes and Listeria innocua mutants lacking the prolipoprotein diacylglyceryl transferase (lgt) gene are unable to induce TLR2-dependent activation of NF-B, a property intrinsic to their isogenic parental strains. TLR2-dependent immune recognition is directed to secreted, soluble lipoproteins as evidenced by the sensitivity of the response to lipoprotein lipase. Studies of bone marrow-derived macrophages of C57BL/6 wild-type and TLR2-deficient mice infected with wild-type and lgt mutant strains indicate that the absence of host TLR2 receptor signaling has consequences similar to those of the absence of the bacterial TLR2 ligand, i.e., a delay in cellular immune responses directed toward the bacterium. Infection studies with the wild-type and TLR2^–/– mice indicated attenuation of the lgt deletion mutant in both mouse strains, implying multiple roles of lipoproteins during infection. Further characterization of the lgt mutant indicated that it is impaired for both invasion and intracellular survival and exhibits increased susceptibility to cationic peptides. Our studies identify lipoproteins as the immunologically active ligand of TLR2 and assign a critical role for this receptor in the recognition of these bacteria during infection, but they also reveal the overall importance of the lipoproteins for the pathogenicity of Listeria.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by grants from the National Genome Research Network through the Bundesministerium für Bildung und Forschung to T.C.

² S.M. and S.T. contributed equally to this work.

³ Address correspondence and reprint requests to Dr. Svetlin Tchatalbachev, Institut für Medizinische Mikrobiologie, Justus-Liebig-Universität, Frankfurter Strasse 107, D-35392 Giessen, Germany. E-mail address: Svetlin.Tchatalbachev{at}mikrobio.med.uni-giessen.de

⁴ Abbreviations used in this paper: PAMP, pathogen-associated molecular pattern; BHI, brain-heart infusion; MOI, multiplicity of infection; BMM, bone marrow macrophages.