Mucins in normal and diseased airways

Sammanfattning: Mucus glycoproteins (mucins) are the principal constituents of respiratory secretions in health and disease. The increased 'acidity' of mucin producing cells in the bronchitic airways is not reflected in a change of negative charge of bronchitic mucins. Furthermore, the size and macromolecular properties of mucins from chronic bronchitic sputa do not differ significantly from those in normal airways. Antibodies against a peptide within the MUC5AC mucin recognize a distinct mucin population in airway mucus. This mucin is large and oligomeric and immunohistochemistry revealed it to be of goblet cell origin. In addition, another population of large oligomeric mucins was identified in the submucosa, probably originating from the submucosal glands. The MUC2 mucin was shown not to be a prominent mucin in airway secretions. Bovine trachea was established as a model to study mucin biosynthesis and secretion. The uptake of radioactive glycoprotein precursors by mucin producing cells was monitored by autoradiography and 35S-sulphate, in particular, was incorporated into secreted as well as intracellular mucins. Radiolabelled mucins, secreted into the medium, were smaller and had a higher byoyant density than the predominant species identified in tracheal lavage. The trachea in organ culture may thus not correspond to those secreted by the intact tissue. This observation may have important consequences for the interpretation of data on the synthesis and secretion of mucus-glycoproteins in vitro.