The claudin superfamily consists of many structurally related proteins that are important structural and functional components of tight junctions in paracellular transport. Claudins are located in both epithelial and endothelial cells in all tight junction-bearing tissues. Claudins, which consist of four transmembrane domains and two extracellular loops, make up tight junction strands. It is suggested that the claudin family of proteins regulate transport through tight junctions via differential discrimination for solute size and charge. Claudin expression is often highly restricted to specific regions of different tissues and may have an important role in transcellular transport through tight junctions. Claudin-22, also known as CLDN22, is a 220 amino acid member of the claudin family that participates in tight junction-specific obliteration of the intercellular space through calcium-independent cell-adhesion activity.