TGF-β1 staining is prominent in the IPF lung, and active TGF-β1 concentrations are elevated in IPF BAL specimens, far exceeding TGF-β2 and TGF-β3 levels (whereas free TGF-β3 levels are highest in healthy lung BAL) (50). Here, TGFB1 is linked to idiopathic pulmonary fibrosis.