Pathophysiology and treatment of airway mucociliary clearance. A moving tale.

Airway hygiene depends largely on mucociliary clearance (MCC) which in turn depends upon the movement of viscoelastic mucus along the airway by the beating of the ciliary appendages of airway epithelial cells. Failure to keep the airways sterile by MCC results in a host inflammatory response to the persistent microorganisms which, if it becomes chronic, causes damage to the airway wall and upregulation of mucus production manifest clinically as bronchiectasis, sinusitis and otitis. There are three principal disorders of MCC. Firstly, primary ciliary dyskinesia (PCD), a rare genetic deficiency of the ultrastructural apparatus required to propel the cilium, in which nasal nitric oxide is very low due to a deficiency of inducible nitric oxide synthase. Secondly, secondary ciliary dyskinesia due principally to microbial toxin-induced dysfunction of the energy pathways required for ciliary beating. Thirdly, abnormalities in the physicochemical properties of mucus, including reduced salt content/osmolality which results in it being unsuitable in quality for cilia to move it. Methods of rectifying this defect promise to restore MCC to normal and interfere in the vicious circle of inflammatory lung damage.