MUC5AC and chronic obstructive pulmonary disease: The increased expression of MUC5AC has been reported in the bronchiolar epithelium and submucosal glands, whose tendency is inversely related to forced expiratory volume in 1 s percent predicted (FEV1% pred) against chronic obstructive pulmonary disease (COPD) in clinical practice (Leikauf et al., 2002; Caramori et al., 2009).