Host defense mechanisms of the respiratory epithelium. Cough and cilia mechanically remove inhaled debris and microorganisms entrapped in mucus, a mechanism called mucociliary clearance. Multiple substances with pro- and antiinflammatory as well as antimicrobial activities are secreted by epithelial cells and function as an innate immune barrier. Macrophages, B and T lymphocytes, neutrophils and also epithelial cells represent cellular components of the innate and adaptive immune systems.
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