Desquamative
interstitial pneumonia (DIP) is a rare, smoking-related,
diffuse parenchymal lung disease characterized by marked accumulation of alveolar macrophages (AMs) and
emphysema, without extensive
fibrosis or neutrophilic
inflammation. Because smoking increases expression of pulmonary
GM-CSF (
granulocyte/macrophage-colony stimulating factor) and
GM-CSF stimulates proliferation and activation of AMs, we hypothesized that chronic exposure of mice to increased pulmonary
GM-CSF may recapitulate DIP. Wild-type (WT) mice were subjected to inhaled cigarette
smoke exposure for 16 months, and AM numbers and pulmonary
GM-CSF mRNA levels were measured. After demonstrating that
smoke inhalation increased pulmonary
GM-CSF in WT mice, transgenic mice overexpressing pulmonary
GM-CSF (SPC-
GM-CSF+/+) were used to determine the effects of chronic exposure to increased pulmonary
GM-CSF (without
smoke inhalation) on accumulation and activation of AMs, pulmonary
matrix metalloproteinase (
MMP) expression and activity, lung histopathology, development of
polycythemia, and survival. In WT mice,
smoke exposure markedly increased pulmonary
GM-CSF and AM accumulation. In unexposed SPC-
GM-CSF+/+ mice, AMs were spontaneously activated as shown by phosphorylation of STAT5 (signal inducer and activator of transcription 5) and accumulated progressively with involvement of 84% (interquartile range, 55-90%) of the lung parenchyma by 10 months of age. Histopathologic features also included scattered multinucleated giant cells, alveolar epithelial cell
hyperplasia, and mild alveolar wall thickening. SPC-
GM-CSF+/+ mice had increased pulmonary MMP-9 and MMP-12 levels, spontaneously developed
emphysema and secondary
polycythemia, and had increased mortality compared with WT mice. Results show cigarette
smoke increased pulmonary
GM-CSF and AM proliferation, and chronically increased pulmonary
GM-CSF recapitulated the cardinal features of DIP, including AM accumulation,
emphysema, secondary
polycythemia, and increased mortality in mice. These observations suggest pulmonary
GM-CSF may be involved in the pathogenesis of DIP.