IFNG and idiopathic pulmonary fibrosis: NHLFs and IPF fibroblasts were incubated with INF-γ, PFD and a combination of IFN-γ/PFD in the presence of TGF − β1 (2.5 ng/mL) or PDGF-BB (20 ng/ml) for 1, 3 and 5 days.