The limited duration of IPF PCLS viability combined with the slow progression of native disease (no exogenous fibrogenic factors [e.g. TGF-β or bleomycin] were added to the human PCLS cultures to increase fibrogenesis) also precluded evaluation of drug-induced changes in interstitial collagen protein levels. This evidence concerns the gene TGFB1 and idiopathic pulmonary fibrosis.