Background—Treatment with an antibody that binds β₃ integrins (abciximab; c7E3 Fab) at the time of coronary angioplasty decreases the need for repeat revascularization. Two potential mechanisms have been proposed to explain this effect: (1) inhibition of platelet aggregation or (2) interruption of ligand binding to β₃ integrins on the smooth muscle cell (SMC) surface. We examined the latter hypothesis by determining (1) if β₃ integrin expression is upregulated after vascular injury in the baboon, (2) if 7E3 binds β₃ integrins on cultured SMC, and (3) if β₃ integrin activation plays a role in proliferation of cultured SMC.

Methods and Results—Results demonstrated that immunostaining for β₃ integrins was present in the neointima 1 week after balloon withdrawal injury of baboon brachial arteries and that β₃ integrin expression colocalized with α-actin–positive cells. In contrast, staining for β₃ integrins was undetectable in contralateral uninjured brachial arteries. 7E3 bound to cultured human aortic SMC with an affinity (K_D=3.3 nmol/L) similar to 7E3 binding to endothelial cells or platelets. Cotreatment with 7E3 partially inhibited thrombospondin-induced or α-thrombin–induced proliferation but not PDGF-induced or serum-induced proliferation.

Conclusions—In summary, these studies demonstrate that vascular cell β₃ integrin expression is increased after injury, that 7E3 binds to cultured SMC with high affinity, and that β₃ activation is important for thrombospondin-induced or α-thrombin–induced proliferation. These results support the hypothesis that β₃ integrins play a role in SMC growth responses after balloon injury.