TGFB1 and pulmonary fibrosis: In order to determine whether cellular senescence is accelerated during pulmonary fibrosis induced by SWCNTs, we firstly examined the expressions of p21, p16 and SASP (TGF-β and PAI-1) in lung tissues from mice challenged with SWCNTs exposure after days 3, 7 and 28 (Fig. 1A).