TLR4-dependent GM-CSF protects against lung injury in Gram-negative bacterial pneumonia

Am J Physiol Lung Cell Mol Physiol. 2012 Mar 1;302(5):L447-54. doi: 10.1152/ajplung.00415.2010. Epub 2011 Dec 9.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Acute Lung Injury / metabolism
  • Acute Lung Injury / microbiology*
  • Acute Lung Injury / prevention & control
  • Animals
  • Apoptosis
  • Bacterial Load
  • Bronchoalveolar Lavage Fluid / microbiology
  • Cells, Cultured
  • Cytoprotection
  • Granulocyte-Macrophage Colony-Stimulating Factor / metabolism
  • Granulocyte-Macrophage Colony-Stimulating Factor / pharmacology
  • Granulocyte-Macrophage Colony-Stimulating Factor / physiology*
  • Granulocyte-Macrophage Colony-Stimulating Factor / therapeutic use
  • Klebsiella Infections / drug therapy
  • Klebsiella Infections / metabolism
  • Klebsiella Infections / microbiology*
  • Klebsiella pneumoniae*
  • Lung / metabolism
  • Lung / microbiology
  • Lung / pathology
  • Mice
  • Mice, Inbred BALB C
  • Pneumonia, Bacterial / drug therapy
  • Pneumonia, Bacterial / metabolism
  • Pneumonia, Bacterial / microbiology*
  • Respiratory Mucosa / drug effects
  • Respiratory Mucosa / metabolism
  • Respiratory Mucosa / physiopathology
  • Time-Lapse Imaging
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism*


  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Granulocyte-Macrophage Colony-Stimulating Factor