Triggering of β1-integrin chain induces platelet adhesion to cultured endothelium

Abstract

We report here that platelets adhere to cultured endothelial cells (EC) on exposure to the integrin β1 activating monoclonal antibody (mAb) BV7. The effect of BV7 is exerted mostly on platelets rather than EC. BV7 does not induce platelet aggregation or 5-hydroxytryptamine (5-HT) release and does not increase platelet adhesion to matrix proteins. Another activating β1 mAb, Lia1/2, triggers an effect similar to BV7. Blocking antibodies to α2 and β1, but not to other integrin chains, are able to inhibit BV7-mediated adhesion. Moreover, the effect of BV7 requires active cellular metabolism and is not inhibited by platelet treatment with aspirin, by the PAF receptor antagonist BN50730, the phosphokinase C inhibitor staurosporin, or by the cAMP or cGMP enhancers prostaglandin E1 and sodium nitroprusside, respectively. Finally, BV7-mediated adhesion was enhanced by the endoperoxide analogue U46619. These data describe a novel mechanism of platelet adhesion to endothelial cells. This adhesion pathway appears to be mediated by α2β1- integrin on platelets and a still-undefined endothelial counter receptor.