[Growth factors in the process of inflammation and fibrosis in the lung]

Growth factors are known not only to cause a mitogenic response and alter differentiated characteristics of the target cells, but also to play important roles in intercellular signaling. Many growth factors are expressed in the embryonic and regulate embryogenesis. Pulmonary fibrosis is characterized by a complex process involving chronic inflammatory reaction, fibroblast proliferation, and abnormal deposition of interstitial collagen as a result of excess healing reaction. In the early phases, TNF-alpha, IL-beta and GM-CSF secreted by alveolar macrophages regulate and enhance pulmonary inflammation. On the contrary, TGF-alpha, KGF and HGF have been reported to enhance repair of alveolar epithelium and vascular endothelium in the injured lung. Furthermore, growth factors produced by alveolar macrophages and epithelium, such as PDGF, TGF-beta and activin A and belongs to the TGF-beta supergene family are known to play cardinal roles in fibroblast proliferation and pulmonary fibrosis. Further works concerning this complex growth factors (cytokines) network are required to provide a basis of the pathophysiology of pulmonary fibrosis.