FIG 1.

Healthy and impaired respiratory epithelial barrier. Adjacent pseudostratified columnar ciliated airway cells are interconnected by TJ, adherens junctions, and desmosomes. Respiratory epithelium sits on basal membrane, attached to lamina propria. Neuronal TRPs are expressed in epithelial cells and regulate permeability of barriers. When disrupted by increased temperature, airborne allergens, and pollution, TJ proteins such as zonula occludens–associated occludin, claudin, and JAM are disrupted and epithelial junctions open. TRPV1 and TRPV4 are upregulated; HSP-70, HSP-90, and HSP-72 are increased, and ROS are formed. All these cause increased inflammation, increased paracellular permeability, increased mucus, reduced ciliary movement, damaged cilia, and epithelial shedding. JAM, Junctional adhesion molecules; ROS, reactive oxygen species.