These discrepancies could be explained by various facts including: 1) dose-dependent effects of TGF-β, 2) differences in cell types (nasal epithelial versus bronchial epithelial cells, cell lines versus primary cultures), primary culture methods (submerged versus air-liquid interface), or 3) disease entity (asthma versus CF). This evidence concerns the gene TGFB1 and cystic fibrosis.