Macrophage tumor necrosis factor-alpha induces epithelial expression of granulocyte-macrophage colony-stimulating factor: impact on alveolar epithelial repair

Am J Respir Crit Care Med. 2009 Sep 15;180(6):521-32. doi: 10.1164/rccm.200812-1837OC. Epub 2009 Jul 9.


Rationale: Resident alveolar macrophages have been attributed a crucial role in host defense toward pulmonary infection. Their contribution to alveolar repair processes, however, remains elusive.

Objectives: We investigated whether activated resident alveolar macrophages contribute to alveolar epithelial repair on lipopolysaccharide (LPS) challenge in vitro and in vivo and analyzed the molecular interaction pathways involved.

Methods: We evaluated macrophage-epithelial cross-talk mediators for epithelial cell proliferation in an in vitro coculture system and an in vivo model of LPS-induced acute lung injury comparing wild-type, granulocyte-macrophage colony-stimulating factor (GM-CSF)-deficient (GM(-/-)), and human SPC-GM mice (GM(-/-) mice expressing an SPC-promotor-regulated GM-CSF transgene).

Measurements and main results: Using reverse transcription-polymerase chain reaction and ELISA we showed that LPS-activated alveolar macrophages stimulated alveolar epithelial cells (AEC) to express growth factors, particularly GM-CSF, in coculture. Antibody neutralization experiments revealed epithelial GM-CSF expression to be macrophage tumor necrosis factor (TNF)-alpha dependent. GM-CSF elicited proliferative signaling in AEC via autocrine stimulation. Notably, macrophage TNF-alpha induced epithelial proliferation in wild-type but not in GM-CSF-deficient AEC as shown by [(3)H]-thymidine incorporation and cell counting. Moreover, intraalveolar TNF-alpha neutralization impaired AEC proliferation in LPS-injured mice, as investigated by flow cytometric Ki-67 staining. Additionally, GM-CSF-deficient mice displayed reduced AEC proliferation and sustained alveolar barrier dysfunction on LPS treatment compared with wild-type mice.

Conclusions: Collectively, these findings indicate that TNF-alpha released from activated resident alveolar macrophages induces epithelial GM-CSF expression, which in turn initiates AEC proliferation and contributes to restoring alveolar barrier function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Enzyme-Linked Immunosorbent Assay
  • Epithelial Cells / immunology
  • Epithelial Cells / pathology
  • Flow Cytometry
  • Granulocyte-Macrophage Colony-Stimulating Factor / biosynthesis*
  • Granulocyte-Macrophage Colony-Stimulating Factor / immunology
  • In Vitro Techniques
  • Inflammation Mediators / immunology
  • Lipopolysaccharides / pharmacology
  • Lung / immunology
  • Lung / pathology
  • Lung Injury / immunology*
  • Lung Injury / pathology
  • Macrophage Activation / immunology*
  • Macrophages, Alveolar / immunology*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Reverse Transcriptase Polymerase Chain Reaction
  • Tumor Necrosis Factor-alpha / immunology*


  • Inflammation Mediators
  • Lipopolysaccharides
  • Tumor Necrosis Factor-alpha
  • Granulocyte-Macrophage Colony-Stimulating Factor