title: NOD2 signaling contributes to host defense in the lungs against Escherichia coli infection.
abstract: Bacterial pneumonia remains a significant cause of mortality in the United States. The innate immune response is the first line of defense against invading bacteria. Neutrophil recruitment to the lungs is the first step in a multistep sequence leading to bacterial clearance. Ligand interaction with pattern-recognizing receptors (PRRs) leads to chemokine production, which drives neutrophils to the site of infection. Although we demonstrated that RIP2 is important for host defense in the lungs against Escherichia coli, the individual roles of NOD1 and NOD2 in pulmonary defense have not been addressed. Here, we explored the role of NOD2 in neutrophil-mediated host defense against an extracellular pathogen, E. coli. We found enhanced bacterial burden and reduced neutrophil and cytokine/chemokine levels in the lungs of NOD2⁻/⁻ mice following E. coli infection. Furthermore, we observed reduced activation of NF-κB and mitogen-activated protein kinases (MAPKs) in the lungs of NOD2⁻/⁻ mice upon E. coli challenge. Moreover, NOD2⁻/⁻ neutrophils show impaired intracellular bacterial killing. Using NOD2/RIP2⁻/⁻ mice, we observed bacterial burden and neutrophil accumulation in the lungs similar to those seen with NOD2⁻/⁻ mice. In addition, bone marrow-derived macrophages obtained from NOD2/RIP2⁻/⁻ mice demonstrate a reduction in activation of NF-κB and MAPKs similar to that seen with NOD2⁻/⁻ mice in response to E. coli. These findings unveil a previously unrecognized role of the NOD2-RIP2 axis for host defense against extracellular Gram-negative bacteria. This pathway may represent a novel target for the treatment of lung infection/inflammation.
authors.affiliation: Laboratory of Lung Biology, Department of Pathobiological Sciences and Center for Experimental Infectious Disease Research, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Balamayooran
authors.initials: B
authors.lastname: Theivanthiran
authors.forename: Sanjay
authors.initials: S
authors.lastname: Batra
authors.forename: Gayathriy
authors.initials: G
authors.lastname: Balamayooran
authors.forename: Shanshan
authors.initials: S
authors.lastname: Cai
authors.forename: Koichi
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Richard A
authors.initials: RA
authors.lastname: Flavell
authors.forename: Samithamby
authors.initials: S
authors.lastname: Jeyaseelan
mesh_terms: D000818:Animals; D058491:Bacterial Load; D016207:Cytokines / Q000378:metabolism; D004927:Escherichia coli Infections / Q000276:immunology*; D005260:Female; D008168:Lung / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009504:Neutrophils / Q000276:immunology / Q000382:microbiology; D053473:Nod2 Signaling Adaptor Protein / Q000172:deficiency / Q000276:immunology*; D018410:Pneumonia, Bacterial / Q000276:immunology* / Q000382:microbiology; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000172:deficiency / Q000276:immunology*; D015398:Signal Transduction
chemical_list: D016207:Cytokines; D053473:Nod2 Signaling Adaptor Protein; C495945:Nod2 protein, mouse; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C506255:Ripk2 protein, mouse