This level of TGF-β1 in small airway epithelial tissue is supported by previous studies (27, 38), however other studies have shown an increase in TGF-β1 mRNA and protein in bronchiolar and alveolar epithelium in COPD patients, contradicting the findings of this study (39, 40). This evidence concerns the gene TGFB1 and chronic obstructive pulmonary disease.