Functional defense mechanisms of the nasal respiratory epithelium

The sinonasal mucosa is exposed to large quantities of particulates, antigens, and potential pathogens. To address these possible threats, the human sinonasal epithelium has developed a range of protective functions that effectively clear foreign material with minimal collateral tissue damage. This barrier to the outside world is both physical and immunological in nature. The physical barrier consists of respiratory mucus and mucociliary flow as well as the intact epithelial cell layer. When these structural or clearance mechanisms fail, the epithelium plays an important role in activating a subsequent immune response. The immunologic barrier encompasses the recognition of foreign material via pattern-recognition receptors, which then facilitates the innate and adaptive responses. Understanding these defense mechanisms provides insight into the pathophysiology of inflammatory disorders such as chronic rhinosinusitis.