Among vascular cell adbesio, molecules, platelet-endothelial cell adhesion molecule (PECAM-1/CD31) has the distinctive feature of being expressed on several of the major cell types associated with the vascular compartment. This makes it uniquely positioned to mediate multiple and important cell-cell interactions involving plate! ets, leukocytes and endothelial cells. Thus, PECAM-1 may represent a potential target for new therapeutic agents directed at a variety of pathological states.

The PECAM-I/CD31 antigen was first identified in the mid-1980s following the sereological characterization of cell-surface proteins of vascular cells I-4. Antibodies directed against this protein were found to bind neutrophils and monocytes, and inhibited chemotaxis of~ hese cells towards endotoxin-activ~ ted serum I. Furthcrmore, these antibodies recognized a 130kDa protein present on endothelial cells and platelets-', and identified stem cells of the myeloid lineage-~. Subsequent studies identified this protein as an endothelial cell iunction molecule so. In 1990, Newman et al.-reported the molecular cloning of a 130kDa cellsurface protein designated platelet-endothelial cell adhesioa molecule (PECAM-1). Since then, there has been considerable progress in understanding the structural and function; q aspects of this molecule. Out of these efforts has emerged the concept of PECAM-1 as a vascular ceil adhesion molecule involved in diverse processes and capable of multiple ligand interactions.