When allergen is inhaled it comes into contact with the epithelium of the respiratory tract. This contact triggers multiple events that can ultimately stimulate development of allergic asthma. Some allergens, like house dust mite, contain active proteolytic enzymes that break down tight epithelial cell junctions. Others act to enhance inflammation by stimulating epithelial cells to make proinflammatory cytokines and chemokines. Alterations in airways include mucous cell metaplasia and eosinophil recruitment. In this review, cell culture experiments as well as several animal models and human patient data are utilized to examine the mechanisms by which allergens alter the normal epithelial homeostasis. Environmental pollutants, such as ozone and environmental tobacco smoke, enhance allergen-mediated effects on epithelium.
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