ACTA1 and idiopathic pulmonary fibrosis: Given the importance of fibroblasts in the pathogenesis of IPF, we further address the issue by characterizing fibroblasts derived from lung biopsies of IPF patients in terms of proliferation rate, morphology, and expression of α-SMA (a myofibroblast marker), with a special focus on the connection of these characteristics to replicative and stress-induced CS.