MUC5AC and cystic fibrosis: An altered airway surface environment as seen in CF (decreased Cl− and HCO3− concentration, lowered airway surface pH and dehydration [52,87,88]) may cause failure in the uncoupling of mucin polymer interactions that are active in intragranular packaging, thus negatively affecting the transition from the non-covalently, cross-linked intragranular form to the more expanded linear architecture in mucus [28,72].