TGFB1 and cystic fibrosis: To assess if PFD interferes with the canonical TGF-β1 signaling in human CF, confluent cell cultures of human CF were pre-incubated with 0, 0.3, or 1.0 mg/ml PFD in FGM-3 for 4 h before 5 ng/ml TGF-β1 was added for 30 min.