We found that in comparison to normal human pulmonary fibroblasts, the IPF fibroblast cultures displayed (i) some CS-like morphological features (e.g. enlarged cell and nucleus size, irregular cell form, heterogeneity of cell morphotypes) even in the proliferating stage, and also (ii) a high resistance of proliferating cells to oxidative stress-induced CS and cytotoxicity; (iii) despite this, the IPF fibroblasts showed an accelerated entry to replicative CS accompanied by an accumulation of senescent cells with features of myofibroblasts (high expression of α-SMA). The gene discussed is ACTA1; the disease is idiopathic pulmonary fibrosis.