title: Salmonella enterica serovar Typhimurium ΔmsbB triggers exacerbated inflammation in Nod2 deficient mice.
abstract: The intracellular pathogen Salmonella enterica serovar Typhimurium causes intestinal inflammation characterized by edema, neutrophil influx and increased pro-inflammatory cytokine expression. A major bacterial factor inducing pro-inflammatory host responses is lipopolysaccharide (LPS). S. Typhimurium ΔmsbB possesses a modified lipid A, has reduced virulence in mice, and is being considered as a potential anti-cancer vaccine strain. The lack of a late myristoyl transferase, encoded by MsbB leads to attenuated TLR4 stimulation. However, whether other host receptor pathways are also altered remains unclear. Nod1 and Nod2 are cytosolic pattern recognition receptors recognizing bacterial peptidoglycan. They play important roles in the host's immune response to enteric pathogens and in immune homeostasis. Here, we investigated how deletion of msbB affects Salmonella's interaction with Nod1 and Nod2. S. Typhimurium Δ msbB-induced inflammation was significantly exacerbated in Nod2-/- mice compared to C57Bl/6 mice. In addition, S. Typhimurium ΔmsbB maintained robust intestinal colonization in Nod2-/- mice from day 2 to day 7 p.i., whereas colonization levels significantly decreased in C57Bl/6 mice during this time. Similarly, infection of Nod1-/- and Nod1/Nod2 double-knockout mice revealed that both Nod1 and Nod2 play a protective role in S. Typhimurium ΔmsbB-induced colitis. To elucidate why S. Typhimurium ΔmsbB, but not wild-type S. Typhimurium, induced an exacerbated inflammatory response in Nod2-/- mice, we used HEK293 cells which were transiently transfected with pathogen recognition receptors. Stimulation of TLR2-transfected cells with S. Typhimurium ΔmsbB resulted in increased IL-8 production compared to wild-type S. Typhimurium. Our results indicate that S. Typhimurium ΔmsbB triggers exacerbated colitis in the absence of Nod1 and/or Nod2, which is likely due to increased TLR2 stimulation. How bacteria with "genetically detoxified" LPS stimulate various innate responses has important implications for the development of safe and effective bacterial vaccines and adjuvants.
authors.affiliation: Institute for Experimental Medicine, University of Kiel, Kiel, Germany; Division Models of Inflammation, Research Center Borstel, Borstel, Germany.
authors.forename: Anne-Kathrin
authors.initials: AK
authors.lastname: Claes
authors.affiliation: Institute for Experimental Medicine, University of Kiel, Kiel, Germany; Division Models of Inflammation, Research Center Borstel, Borstel, Germany.
authors.forename: Natalie
authors.initials: N
authors.lastname: Steck
authors.affiliation: Institute for Experimental Medicine, University of Kiel, Kiel, Germany; Division Models of Inflammation, Research Center Borstel, Borstel, Germany.
authors.forename: Dorothee
authors.initials: D
authors.lastname: Schultz
authors.affiliation: Division Immunochemistry, Research Center Borstel, Borstel, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Zähringer
authors.affiliation: Institute of Clinical Molecular Biology; University of Kiel, Kiel, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Lipinski
authors.affiliation: Institute of Clinical Molecular Biology; University of Kiel, Kiel, Germany.
authors.forename: Philip
authors.initials: P
authors.lastname: Rosenstiel
authors.affiliation: Department of Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Geddes
authors.affiliation: Department of Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Dana J
authors.initials: DJ
authors.lastname: Philpott
authors.affiliation: Division of Innate Immunity, Research Center Borstel, Member of the Airway Research Center North (ARCN) of the German Center for Lung Research (DZL), Borstel, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Heine
authors.affiliation: Institute for Experimental Medicine, University of Kiel, Kiel, Germany; Division Models of Inflammation, Research Center Borstel, Borstel, Germany.
authors.forename: Guntram A
authors.initials: GA
authors.lastname: Grassl
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D057809:HEK293 Cells; D006801:Humans; D007249:Inflammation / Q000382:microbiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053473:Nod2 Signaling Adaptor Protein / Q000235:genetics / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D019779:Salmonella enterica / Q000472:pathogenicity*
chemical_list: D017931:DNA Primers; D053473:Nod2 Signaling Adaptor Protein; C495945:Nod2 protein, mouse