title: Myeloid differentiation protein-2-dependent and -independent neutrophil accumulation during Escherichia coli pneumonia.
abstract: Bacterial pneumonia remains a serious disease. Pattern recognition receptors play an integral role in neutrophil accumulation during pneumonia. Although myeloid differentiation protein (MD)-2 has been recognized as a key molecule for LPS signaling, the role of MD-2 in neutrophil accumulation in the lung during bacterial infection has not been explored. Here, we investigate the role of MD-2 in Escherichia coli LPS-induced lung inflammation and E. coli-induced pneumonia. LPS-induced CD14-independent neutrophil accumulation was abolished in CD14/MD-2(-/-) mice. MD-2(-/-) mice challenged with LPS displayed attenuated neutrophil influx, NF-kappaB activation, cytokine/chemokine expression, and lung histopathology. MD-2(-/-) mice transplanted with MD-2(+/+) bone marrow demonstrated decreased neutrophil influx and cytokine/chemokine expression in the lungs when challenged by LPS. MD-2(-/-) mice infected with E. coli demonstrated reduced neutrophil influx and cytokine/chemokine expression in the lungs, whereas heat-killed E. coli did not induce either neutrophil accumulation or cytokine/chemokine expression in MD-2(-/-) mice infected with E. coli. Furthermore, MD-2(-/-) mice displayed increased bacterial burden in the lungs and enhanced bacterial dissemination. Toll-like receptor (TLR)-5(-/-) mice infected with E. coli exhibited attenuated neutrophil accumulation, whereas MD-2/TLR5(-/-) mice inoculated with E. coli showed further attenuated neutrophil influx and impaired bacterial clearance. Taken together, these new findings demonstrate: (1) the important role of MD-2 in the CD14-independent LPS-mediated cascade of neutrophil influx; (2) the relative importance of bone marrow- and non-bone marrow cell-derived MD-2 in LPS-induced inflammation; and (3) the essential role of MD-2-dependent and MD-2-independent (TLR5) signaling in E. coli-induced neutrophil accumulation and pulmonary host defense.
authors.affiliation: Laboratory of Lung Biology, Department of Pathobiological Sciences and Center for Experimental Infectious Disease Research, Louisiana State University (LSU), Baton Rouge, Louisiana 70803, USA.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Cai
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Zemans
authors.forename: Scott K
authors.initials: SK
authors.lastname: Young
authors.forename: G Scott
authors.initials: GS
authors.lastname: Worthen
authors.forename: Samithamby
authors.initials: S
authors.lastname: Jeyaseelan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D018893:Bronchoalveolar Lavage; D004926:Escherichia coli / Q000378:metabolism*; D004927:Escherichia coli Infections / Q000378:metabolism / Q000382:microbiology*; D005260:Female; D005408:Flagellin / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism; D051218:Lymphocyte Antigen 96; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism*; D011014:Pneumonia / Q000378:metabolism / Q000382:microbiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; C411728:Ly96 protein, mouse; D051218:Lymphocyte Antigen 96; D016328:NF-kappa B; D005408:Flagellin