MUC5ACMUC5B

MUC5AC and MUC5B are gel-forming mucins produced by goblet cells and submucosal glands of the airway and other mucosal surfaces. They are encoded by the MUC5AC and MUC5B genes and are major components of respiratory mucus.

These proteins are large, heavily glycosylated glycoproteins with extensive tandem repeat regions that contribute to the viscous gel of mucus. They form disulfide-linked dimers and higher-order polymers, and their glycosylation supports hydration and protection from proteolysis.

MUC5B is the dominant gel-forming mucin in airway secretions, particularly from submucosal glands; MUC5AC is produced mainly by goblet cells in the surface epithelium, with levels that rise in inflammatory or allergic states.

Together they contribute to the viscoelastic properties of mucus and to mucociliary clearance. The relative abundance and composition of MUC5AC and MUC5B influence mucus rheology and transport; imbalances can promote mucus plugging and impaired clearance in conditions such as asthma, chronic obstructive pulmonary disease, and chronic rhinosinusitis.

Genetic variation in the MUC5B promoter, notably rs35705950, increases MUC5B expression and is a strong risk factor for idiopathic pulmonary fibrosis, highlighting the links between mucin biology and lung disease.