Integrins are a large and broadly distributed family of adhesion receptors. Each member is a noncovalent heterodimer composed of an alpha and a beta subunit. The key to the many functions of integrins is their capacity to rapidly modulate their affinity for ligands, to recognize multiple and structurally unrelated ligands, to engage these ligands in a divalention-dependent manner, and mediate intracellular signaling events. Development of a molecular understanding of these central properties of integrins is a major goal of the laboratory. Mutagenesis, expression, biophysical, immunochemical and functional analyses are employed in our studies. Integrins of particular interest are alphaMbeta2, which plays a pivotal role in leukocyte responses during inflammation, and alphaIIbbeta3, which mediates platelet aggregation. Plasminogen is the precursor of the proteolytic enzyme plasmin. In addition to its central role in fibrinolysis, plasmin(ogen) is also involved in cell migration, a function that depends on plasminogen receptors on the surfaces of cells. Ex vivo and in vivo analyses are being performed to determine the roles of plasminogen and its receptors in inflammatory responses.