Immune Functions of Airway Epithelium
On a daily basis, epithelial cells that line the mucosal surface of the human airways are exposed to around10,000 liters of air,which consists of a complexmixture of gases, particulates, dust, bacteria, viruses, allergens, and other toxic substances. In addition to providing a tight physical barrier, thereby preventing theentryof harmful substances,airwayepithelialcellsplayan integral role in the airway defensemechanisms via their mucociliary action and secretion of awide array of mediators. Recently, substantial evidence has emerged indicating that airwayepithelialcellsalsoserveasan importantpartof thelocal immunesystem. They have the capacity to act as phagocytic as well as antigen-presenting cells and produce and release awide range of biologically active compounds, including lipidmediators,peptides,reactiveoxygenspecies,growth factors,cytokines, and chemokines,which have an important role not only in normal physiological processes but also in the initiation and progression of various airway in£ammatory disorders. Airway epithelial cells are also believed to have a crucial role in airway remodeling by secreting various growth factors that drive smooth muscle,vascular, and neuronal proliferation and deposition of matrix including collagen. This chapter describes our current understanding of the immune functions of the airway epitheliumand its role in the pathogenesis of asthma.