MUC5B and pulmonary fibrosis: MUC5B/AC, and their glycoforms contribute to the elasticity and viscous nature of the mucus layer covering epithelium.45 Mice with Muc5b deficiency develop spontaneous pulmonary pathology from chronic bacterial infection.46 Distinctive to MUC5B, production of MUC5AC is often associated with pathogenesis of respiratory diseases such as asthma or lung fibrosis.