Defects in the TGFβ1 gene resulting in increased TGFβ1 production, or locally induced TGFβ1 increases may only be sufficient to cause a fibrotic injury when acting in concert with other factors, thus reinforcing the hypothesis that IPF development is due to the interplay of a number of factors. This evidence concerns the gene TGFB1 and idiopathic pulmonary fibrosis.