AECs trans-differentiate into fibroblasts through epithelial-mesenchymal transition (EMT), a process requiring prolonged exposure to TGFβ for nearly 2 weeks, and AECs overlying fibroblastic foci in IPF/UIP appear histologically similar to fibroblasts, suggesting ongoing EMT (13). This evidence concerns the gene TGFB1 and idiopathic pulmonary fibrosis.