In humans and mice, the first line of innate defense against inhaled pathogens and particles in the respiratory tract is airway mucus. Mucus is a gel consisting of water, ions, proteins, and macromolecules. The major macromolecular components of mucus are the mucin glycoproteins, which are critical for local defense of the airway. In normal physiological conditions, mucins have diverse functions, such as the proliferation of cells, inflammation, immune response, and cell-cell adhesion. MUC5B is employed for MCC in regular maintenance of a healthy respiratory tract, and MUC5AC is primarily produced in response to acute respiratory inflammation for reasons that are not entirely clear. MUC5AC and MUC5B expression varies among individuals, but the overall result is excessive mucin production in COPD, Asthma, NCFB ,CF and IPF.
Mucin in health and disease (Ridley et al. 2018).