The coxsackievirus and adenovirus receptor (CAR) mediates cell attachment and infection by coxsackie B viruses and by a number of adenoviruses. CAR also mediates homotypic intercellular interactions. In polarized epithelial cells, CAR is closely associated with the tight junction, where it contributes to the barrier to paracellular flow of solutes and macromolecules. CAR's biological roles are not well defined, but emerging evidence suggests that it may function during embryonic development and in regulating cell proliferation.