Clara cell protein 16 release from the nasal mucosa in allergic rhinitis, chronic rhinosinusitis, and exposure to air pollutants.

Clara cell protein 16 (CC16) is a small protein mainly produced by non-ciliated Clara cells in the respiratory epithelium. It has an anti-inflammatory role in chronic upper and lower airway eosinophilic inflammations. Decreased levels of CC16 are found in the nasal secretions and plasma of patients with chronic eosinophilic inflammatory disorders, such as asthma, allergic rhinitis, and chronic rhinosinusitis with or without nasal polyps, as well as in people exposed to high levels of air pollutants. Intranasal corticosteroid administration suppresses chronic inflammation of the nasal mucosa driven by eosinophils and stimulates local CC16 production. CC16 can be a reliable biomarker of the beneficial effects of perennial allergic rhinitis and chronic rhinosinusitis therapy and of the functional recovery of the nasal mucosa after treatment with topical glucocorticoids.