properties. MUC5AC is the main gel-forming mucin secreted by goblet cells, in the form of threads and thin sheets. MUC5B is a polymeric protein secreted from submucosal glands and some goblet cells, and this is in the form of strands.

In the airways--the trachea, bronchi, and bronchioles--the lining of mucus is produced by specialized airway epithelial cells called goblet cells, and submucosal glands.