MUC5AC protein concentrations are increased in the sputum of patients with asthma during exacerbations compared with patients with stable asthma and controls, whereas concentrations of mucin-5B (MUC5B) are decreased among patients with asthma—ie, alterations in the ratio of MUC5AC to MUC5B are a feature of asthma.57 Here, MUC5B is linked to asthma.