title: TLR4-dependent GM-CSF protects against lung injury in Gram-negative bacterial pneumonia.
abstract: Toll-like receptors (TLRs) are required for protective host defense against bacterial pathogens. However, the role of TLRs in regulating lung injury during Gram-negative bacterial pneumonia has not been thoroughly investigated. In this study, experiments were performed to evaluate the role of TLR4 in pulmonary responses against Klebsiella pneumoniae (Kp). Compared with wild-type (WT) (Balb/c) mice, mice with defective TLR4 signaling (TLR4(lps-d) mice) had substantially higher lung bacterial colony-forming units after intratracheal challenge with Kp, which was associated with considerably greater lung permeability and lung cell death. Reduced expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA and protein was noted in lungs and bronchoalveolar lavage fluid of TLR4 mutant mice postintratracheal Kp compared with WT mice, and primary alveolar epithelial cells (AEC) harvested from TLR4(lps-d) mice produced significantly less GM-CSF in vitro in response to heat-killed Kp compared with WT AEC. TLR4(lps-d) AEC underwent significantly more apoptosis in response to heat-killed Kp in vitro, and treatment with GM-CSF protected these cells from apoptosis in response to Kp. Finally, intratracheal administration of GM-CSF in TLR4(lps-d) mice significantly decreased albumin leak, lung cell apoptosis, and bacteremia in Kp-infected mice. Based on these observations, we conclude that TLR4 plays a protective role on lung epithelium during Gram-negative bacterial pneumonia, an effect that is partially mediated by GM-CSF.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, MI 48109, USA.
authors.forename: Louis R
authors.initials: LR
authors.lastname: Standiford
authors.forename: Theodore J
authors.initials: TJ
authors.lastname: Standiford
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Newstead
authors.forename: Xianying
authors.initials: X
authors.lastname: Zeng
authors.forename: Megan N
authors.initials: MN
authors.lastname: Ballinger
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Kovach
authors.forename: Ajaya K
authors.initials: AK
authors.lastname: Reka
authors.forename: Urvashi
authors.initials: U
authors.lastname: Bhan
mesh_terms: D055371:Acute Lung Injury / Q000378:metabolism / Q000382:microbiology* / Q000517:prevention & control; D000818:Animals; D017209:Apoptosis; D058491:Bacterial Load; D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology; D002478:Cells, Cultured; D019610:Cytoprotection; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology* / Q000627:therapeutic use; D007710:Klebsiella Infections / Q000188:drug therapy / Q000378:metabolism / Q000382:microbiology*; D007711:Klebsiella pneumoniae; D008168:Lung / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D018410:Pneumonia, Bacterial / Q000188:drug therapy / Q000378:metabolism / Q000382:microbiology*; D020545:Respiratory Mucosa / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology; D059008:Time-Lapse Imaging; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*
chemical_list: C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D016178:Granulocyte-Macrophage Colony-Stimulating Factor