MUC5AC and chronic obstructive pulmonary disease: Since chronic mucus hypersecretion and elevated sputum MUC5AC are associated with a long-term decline in forced expiratory volume in 1 second (FEV1) (10, 21), we also hypothesized that the induction of MUC5AC during RV infection would be related to acute lung function changes during COPD exacerbation.