ABSTRACT
The first line of defense to maintain the sterility of the intrapulmonary airways is the mucociliary clearance system. This rapidly responding, non-specific, immune defensive system is challenged by approximately 12,000 liters of air filtered by the lungs each day, containing millions of particles like spores, environmental and eventually toxic pollutants. The main components of this system are the floating mucus "blanket", the underlying mucus propelling cilia with periciliary fluid, and the airway epithelium with secretory and ciliated type of cells. The fine and coordinated regulation of these three components is critical for an effective performance. Deregulation resulting from continuous insults, inherited ion channel disease, infections or abnormal immune response may lead to mucus alterations, goblet cell hyperplasia and metaplasia, airway obstruction, air trapping and chronic lung disease. Options for treatment are limited. Understanding this system may reveal new targets for treatment of lung disease.