However, in addition to the benefit of roflumilast on cough symptoms in COPD patients with chronic bronchitis, the potential mechanisms are the decrease in MUC5AC expression in bronchial epithelium, increases in CFTR dynamic activation of airway epithelium cells, and enhanced ciliary beat of smoke-injured human bronchi (Liu et al., 2005; Mata et al., 2005; Milara et al., 2012). This evidence concerns the gene CFTR and chronic bronchitis.