TGFB1 and chronic rhinosinusitis with nasal polyps: The study was also designed to test whether activin A expression is increased in CRSsNP and is associated with increased TGF-β1 levels, as well as whether the production of follistatin may be involved in the anti-fibrotic milieu in CRSwNP, consistent with the hypothesis that CRSsNP and CRSwNP are two distinct disease entities.