The importance of the interaction between leukocyte integrin Mac-1 and platelet glycoprotein Ib-a for leukocyte recruitment by platelets and for the inflammatory response to vascular injury

OBJECTIVE: To assess the importance of the interaction between leukocyte integrin Mac-1 (a Mb 2) and platelet glycoprotein (GP) Ib-a for leukocyte recruitment after vascular injury and the effect of the neutralization of the Mac-1-GPIba interaction on cell proliferation and the neointimal hyperplasia triggered by the vascular injury. METHODS: A peptide called M2 or anti-M2 antibody was developed to block the Mac-1-GPIba interaction. This peptide was injected and compared to a control-peptide in C57B1/6J mice submitted to vascular injury of the femoral artery with a guide wire. One, five or 28 days after the vascular injury, the femoral arteries were removed for morphometric and immunohistochemical analyses. RESULTS: The blocking of the Mac-1-GPIba interaction promoted a statistically significant reduction in the number of leukocytes in the neointimal layer on the first day after the vascular injury (control: 7.9±5.0% of the cell total versus anti-M2: 2.0±1.6%, p=0.021), as well as determined a statistically significant decrease in leukocyte accumulation in the neointimal layer on days 5 and 28 (control: 42.3±12.9% versus anti-M2: 24.6±10.8%, p=0.047 and control: 7.9±3.0% versus anti-M2: 3.3±1.3%, p=0.012; respectively). Cell proliferation in the neointimal layer of the vessel five days post-injury was reduced with the blocking of the Mac-1-GPIba interaction (control: 5.0±2.9% of the cell total versus anti-M2: 1.8±0.5%; p=0.043), along with a significant decrease in cell proliferation in the vessel neointimal layer 28 days post-injury (control: 3.8±1.7% versus anti-M2: 2.0±1.2%; p=0.047). The blocking of the Mac-1-GPIba interaction also determined a statistically significant decrease of the intimal thickening 28 days post-injury (control: 10,395±3,549 µm² versus anti-M2: 4,561±4,915 µm²; p=0.012). CONCLUSION: Leukocyte recruitment after a vascular injury depends on the Mac-1-GPIba interaction and the neutralization of this interaction inhibits cell proliferation and neointimal formation.