Greene C, Campbell M.
Tight junction proteins are integral membrane proteins located apically on epithelial and endothelial cells. They form a selective paracellular barrier restricting the passage of solutes and ions across epithelial and endothelial sheets. In brain endothelial cells, the enrichment of tight junction proteins is one of the unique features of the blood-brain barrier, the physiological boundary that separates the blood from the parenchyma. The predominant tight junction family proteins are the claudins, but several others have been described in recent years including the marvel family, occludin, and lipolysis-stimulated lipoprotein receptor. Together, the tight junctions create a highly electrical-resistant, impermeable paracellular channel that strictly restricts the movement of material from the blood to the parenchyma and vice versa. In this chapter, we will discuss immunohistochemical methods to assess tight junction expression and localization and an ImageJ-based method for quantifying tight junction staining in healthy and diseased states.