The injured epithelial cells are the primary source of mediators for the development of pulmonary fibrosis, producing a number of growth factors and cytokines, including platelet-derived growth factor, transforming growth factor β (TGF-β), tumor necrosis factor α (TNFα), endothelin-1 and connective tissue growth factor. This evidence concerns the gene TGFB1 and pulmonary fibrosis.