TGFB1 and idiopathic pulmonary fibrosis: However, in IPF, repeated epithelial cell damage elicits and induces abnormal repair responses, in which hyperplastic changes occur in alveolar epithelial cells and profibrotic cytokines are released, especially TGF-β, inducing an epithelial–mesenchymal transition in alveolar epithelial cells, followed by excessive accumulation of the extracellular matrix [1,49].