In COPD, epithelial cells are an important source of inflammatory mediators and proteases and are an important source of transforming growth factor β (TGF-β), a growth factor linked to airflow limitation in small conducting airways and in fibrosis, initiating a perpetuating peribronchial fibrosis remodeling that contributes to small airway obstruction (Milara et al., 2013). Here, TGFB1 is linked to chronic obstructive pulmonary disease.