The airway epithelium occupies a critical environmental interface, protecting the host from a wide variety of inhaled insults, including chemical and particulate pollutants and pathogens. The coordinated regulation of ion and water transport, mucous secretion, and cilia beating underlies mucociliary clearance. Physical trapping and removal of harmful substances, in combination with baseline or inducible secretion of antimicrobial factors, antioxidants, and protease inhibitors and recruitment of nonspecific inflammatory cells (neutrophils, monocytes), constitutes airway innate host defense.
