Epithelial Cells: Structure, Transport, and Barrier Function. Structure, Transport, and Barrier Function

Most mucosal surfaces are lined by a single layer of epithelial cells that mediate transport. These cells also form a physical barrier that prevents pathogens, toxins, and other unwanted materials from entering the body. The paracellular space between adjacent epithelial cells is sealed by the selectively permeable tight junction. Regulation of tight junction permeability is essential for physiologic and pathologic transport in the intestinal epithelium, and loss of barrier function has been implicated in the pathogenesis of immune-mediated diseases. However, it remains unclear as to whether loss of barrier function is a precursor to disease development or results from a local inflammatory response. Using the intestinal epithelium as an example, this chapter explores the regulation of epithelial barrier function in physiological and pathophysiological conditions and the intersection between intestinal paracellular permeability and mucosal immunity.