ABSTRACT
Human physiology requires selective compartmentation so that
distinct physiological functions can be effectively regulated. Central
to organ compartments are barriers composed of specialized
polarized epithelial cells. Epithelial and endothelial cells have
several features that promote barrier function, including apical-
basolateral polarity and intercellular junctions called tight junctions.
Cells also mediate a selective barrier through the cytoplasm of cells
via transcytotic pathways. Each of these elements can be targeted
to alter barrier function. Insights from pathogens that interact with
cells to decrease barrier function provide clues to pharmacologic
agents that can have similar effect to promote drug delivery.