The important role that TGF-β1 may play in this disorder can be seen in studies that demonstrate that TGF-β1 is a critical mediator of pulmonary fibrosis after bleomycin injury (Nakao et al., 1999; Yehualaeshet et al., 2000) and that high dose adenoviral TGF-β1 transfer or lung-specific transgenic expression causes progressive pulmonary fibrosis in vivo (Sime et al., 1997; Kelly et al., 2003; Lee et al., 2004) and IPF-like fibroblastic foci in vitro explants (Xu et al., 2003). Here, TGFB1 is linked to idiopathic pulmonary fibrosis.