title: Mechanical ventilation modulates Toll-like receptor-3-induced lung inflammation via a MyD88-dependent, TLR4-independent pathway: a controlled animal study.
abstract: BACKGROUND
  Mechanical ventilation augments lung inflammation resulting from exposure to microbial products. The objective of this study was to test the hypothesis that ventilator-associated immune modulation requires MyD88-dependent signaling. Because MyD88 is a critical adapter protein utilized for pro-inflammatory signaling by all Toll-like receptors (TLRs), with the exception of TLR3, as well as by the IL-1 and IL-18 receptors, MyD88 dependence would implicate generation of an endogenous soluble ligand recognized by one or more of these receptors during mechanical ventilation and would provide an opportunity for a potential future therapeutic intervention.
  
  
  METHODS
  We compared the effect of mechanical ventilation on lung inflammation and permeability between poly(I:C) exposed mice with or without expression of MyD88. Poly(I:C) is a synthetic ligand for TLR3, the only MyD88-independent TLR, allowing isolation of the effect of MyD88 deletion on ventilator-augmentation of lung inflammation. Lung inflammation was assessed by cytokine concentration in lung tissue homogenate and polymorphonuclear cell (PMN) number in bronchoalveolar lavage fluid (BALF). Lung permeability was assessed by total protein, IgM, and intravenously injected FITC-dextran concentrations in BALF.
  
  
  RESULTS
  We found that MyD88 was required for mechanical ventilation augmentation of TLR3-induced lung inflammation and permeability. Because TLR4 is the most commonly reported receptor for endogenous ligands generated during tissue injury, we performed a second experiment comparing wildtype and TLR4-/- mice. We found that mechanical ventilation increased TLR3-mediated inflammation and permeability independent of TLR4.
  
  
  CONCLUSIONS
  These data support the hypothesis that mechanical ventilation with moderate tidal volumes generates an endogenous ligand(s) recognized by MyD88-dependent receptor(s) other than TLR4, and that this mechanism can contribute to the development of ventilator-associated lung inflammation and injury. Identification of these ligands and/or receptors could lead to new pharmacological treatments for ARDS.
authors.affiliation: Department of Medicine, University of Washington, 1959 NE Pacific St, Seattle, WA 98195, USA.
authors.forename: Carrie D
authors.initials: CD
authors.lastname: Chun
authors.forename: W Conrad
authors.initials: WC
authors.lastname: Liles
authors.forename: Charles W
authors.initials: CW
authors.lastname: Frevert
authors.forename: Robb W
authors.initials: RW
authors.lastname: Glenny
authors.forename: William A
authors.initials: WA
authors.lastname: Altemeier
mesh_terms: D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D002463:Cell Membrane Permeability / Q000502:physiology; D003911:Dextrans / Q000493:pharmacokinetics; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D007075:Immunoglobulin M / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D023421:Models, Animal; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000378:metabolism*; D009504:Neutrophils / Q000166:cytology; D011014:Pneumonia / Q000378:metabolism* / Q000503:physiopathology; D012121:Respiration, Artificial; D015398:Signal Transduction / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D051196:Toll-Like Receptor 3 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*
chemical_list: D003911:Dextrans; D007075:Immunoglobulin M; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; C519703:TLR3 protein, mouse; C493487:Tlr4 protein, mouse; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; C015219:fluorescein isothiocyanate dextran; D016650:Fluorescein-5-isothiocyanate