Proline-rich proteins are present in serous cells of submucosal glands in the respiratory tract.

Using antibodies to basic and acidic proline-rich proteins (PRP) of salivary origin, we detected PRP immunoreactivity in serous cells of human nasal, laryngeal, and tracheobronchial glands by an immunoperoxidase technique. Immunoreactive PRP, detected by immunoblotting from SDS gels, were also found in culture mediums from tracheal explants. We hypothesize that PRP, by interacting with glycoproteins of mucus as other proteins do, may be necessary for maintaining the appropriate viscoelastic properties of respiratory secretions. Thus, PRP may play an important role in disease of the respiratory tract, such as chronic bronchitis, asthma, and cystic fibrosis and may serve important normal functions in addition to those previously identified in the oral cavity.