title: Mild-stretch mechanical ventilation upregulates toll-like receptor 2 and sensitizes the lung to bacterial lipopeptide.
abstract: BACKGROUND
  Mechanical ventilation (MV) could prime the lung toward an inflammatory response if exposed to another insult such as bacterial invasion. The underlying mechanisms are not so far clear. Toll-like receptors (TLRs) allow the host to recognize selectively bacterial pathogens and in turn to trigger an immune response. We therefore hypothesized that MV modulates TLR2 expression and in turn modifies responsiveness to agonists such as bacterial lipopeptide (BLP).
  
  
  METHODS
  Both in vitro and in vivo experiments were conducted. First, TLR2 expression and protein were measured in the A549 pulmonary epithelial cell line submitted to 8-hour cyclic stretch (20% elongation; 20/minute rate). After a 24-hour period of cyclic stretch, the inflammatory response of the A549 cells to the synthetic BLP, Pam3CSK4, was tested after 8 hours of exposure. In a second set of experiments, healthy anesthetized and paralyzed rabbits were submitted to 8-hour MV (tidal volume = 12 ml/kg, zero end-expiratory pressure; FIO2 = 50%; respiratory rate = 20/minute) before being sacrificed for TLR2 lung expression assessment. The lung inflammatory response to BLP was then tested in animals submitted to 24-hour MV before being sacrificed 8 hours after the tracheal instillation of Pam3CSK4.
  
  
  RESULTS
  Cyclic stretch of human pulmonary epithelial cell lines increased both TLR2 mRNA and protein expression. Cells submitted to cyclic stretch also increased IL-6 and IL-8 secretion in response to Pam3CSK4, a classical TLR2 ligand. A mild-stretch MV protocol induced a 60-fold increase of TLR2 mRNA expression in lung tissue when compared with spontaneously breathing controls. Moreover, the combination of MV and airway exposure to Pam3CSK4 acted synergistically in causing lung inflammation and injury.
  
  
  CONCLUSIONS
  Mild-stretch MV increases lung expression of TLR2 and sensitizes the lung to bacterial TLR2 ligands. This may account for the propensity of mechanically ventilated patients to develop acute lung injury in the context of airway bacterial colonization/infection.
authors.affiliation: Laboratoire Interactions Muqueuses Agents Pathogènes, EA562, UFR Médecine, Université de Bourgogne, 7 Bd Jeanne d'Arc, 21000 Dijon, France. pierre-emmanuel.charles@chu-dijon.fr
authors.forename: Pierre-Emmanuel
authors.initials: PE
authors.lastname: Charles
authors.forename: Pierre
authors.initials: P
authors.lastname: Tissières
authors.forename: Saber Davide
authors.initials: SD
authors.lastname: Barbar
authors.forename: Delphine
authors.initials: D
authors.lastname: Croisier
authors.forename: Julien
authors.initials: J
authors.lastname: Dufour
authors.forename: Irène
authors.initials: I
authors.lastname: Dunn-Siegrist
authors.forename: Pascal
authors.initials: P
authors.lastname: Chavanet
authors.forename: Jérôme
authors.initials: J
authors.lastname: Pugin
mesh_terms: D000818:Animals; D001419:Bacteria / Q000378:metabolism*; D018929:Cell Culture Techniques; D004847:Epithelial Cells / Q000378:metabolism / Q000382:microbiology; D005434:Flow Cytometry; D015850:Interleukin-6 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D055666:Lipopeptides / Q000378:metabolism*; D008168:Lung / Q000276:immunology* / Q000378:metabolism; D008297:Male; D011817:Rabbits; D060888:Real-Time Polymerase Chain Reaction; D012121:Respiration, Artificial / Q000379:methods*; D017422:Sequence Analysis, DNA; D051195:Toll-Like Receptor 2 / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D015850:Interleukin-6; D016209:Interleukin-8; D055666:Lipopeptides; D051195:Toll-Like Receptor 2