This concept is supported by the observation that two distinct Smad3 null mutations protect mice from bleomycin-induced lung fibrosis (Bonniaud et al, 2004; Zhao et al, 2002) as well as TGF-β-induced lung fibrosis (Bonniaud et al, 2004; Bonniaud et al, 2005). Here, SMAD3 is linked to pulmonary fibrosis.