Objective: The expression of insulin-like growth factor (IGF)-I and platelet-derived growth factor (PDGF) in open lung biopsies from patients with idiopathic pulmonary fibrosis (IPF) was studied to investigate their precise role in the development of fibrosis in IPF.
Methods: The distribution and expression of IGF-I and PDGF were examined in lung sections of IPF patients with antibodies and cDNA probes of IGF-I and PDGF by immunohistochemistry and in situ hybridization.
Results: IGF-I was predominantly localized in vascular smooth muscle cells and vascular endothelial cells of newly formed vessels in IPF. Smooth muscle cells of pulmonary arteries which underwent hypertrophy and hyperplasia strongly expressed IGF-I (+ + +). Type II cells, alveolar macrophages, and interstitial cells were also stained with anti-IGF-I, but with lesser intensity (+). PDGF-AA and BB were localized in hyperplastic bronchio-alveolar epithelial cells and interstitial fibroblasts (+ + +). Alveolar macrophages, vascular endothelial cells and smooth muscle cells were also stained positive (+ +).
Conclusion: IGF-I and PDGF promote angiogenesis and vascular smooth muscle cell hypertrophy and hyperplasia, which contribute to the progression of fibrosis in IPF. IGF-I and PDGF are also involved in reepithelization and fibroproliferation in IPF through interaction with mesenchymal cells.