Adhesion of cells to one another and to the underlying or surounding extracellular mahix plays crucial roles in the development, physiology andpathology of all metazmns. This is as true in the vasculahrre as anywhere else. Indeed, cell adhesion has been most effectively shrdied in the context of vascular biology; we know more about cell adhesion of vascular cells than about any others and the concepts developed there serve as models for thinking about cell adhesion in other contexts (l).

During development of the vasculature, cell adhesion plays roles in the assembly of the heart and vessels; the cells need to migrate to the correct locations and assemble into tubes, which need to be arrayed correctly. These morphogenetic events rely on cell adhesion; both cell+ ell and ceIl-matrix. If adhesion is improperly regulated during development, abnormalities in the heart or blood vessels can ensue. During normal functioning of the vasculature, circulating cells such as lymphocytes need to adhere in appropriate locations during their traffic around the body. In response to infection or injury, leukocytes need to adhere and extravasate at sites of infection and platelets need to adhere to damaged vessel walls and to each other to prevent bleeding. When these adtresion processes are defective, disease results; susceptibility to infections or bleeding, respectively. While defective adhesion of blood cells is deleterious, so is excessive adhesion. Inappropriate adhesion of leukocytes or plate-lets can lead to inflammation or thrombosis, respectively. Therefore, adhesion must be tightly regulated to give sufficient adhesion when needed and to prevent inappropri-ate or excessive adhesion.