Mondoro T H, Wall C D, White M M, Jennings L K
Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda MD, USA.
Blood. 1996 Nov 15;88(10):3824-30.
Ligand-induced binding sites (LIBS) are neoantigenic regions of glycoprotein (GP)IIb-IIIa that are exposed upon interaction of the receptor with the ligand fibrinogen or the ligand recognition sequence (RGDS). LIBS have been suggested to contribute to postreceptor occupancy events such as full-scale platelet aggregation, adhesion to collagen, and clot retraction. This study examined the induction requirements of a GPIIIa LIBS with regard to ligand specificity. Through the use of the anti-LIBS D3, we report that this complex-activating antibody induces fibrinogen- and von Willebrand factor-binding to GPIIb-IIIa on intact platelets. Bound ligand was detected by flow cytometric analysis and platelet aggregation assays. These bound ligands increased the number of D3-binding sites and altered the affinity of D3 for GPIIb-IIIa on platelets. In contrast, activation of platelet GPIIb-IIIa by D3 did not increase the binding of another RGD-containing ligand, vitronectin. Furthermore, bound vitronectin on thrombin-stimulated platelets did not cause the expression of the D3 LIBS epitope. We conclude direct activation of GPIIb-IIIa in the absence of platelet activation results in selective ligand interaction and that D3 LIBS induction requires the binding of the multivalent ligands, fibrinogen or von Willebrand factor. Thus, the region of GPIIIa recognized by D3 may be an important regulatory domain in ligand-receptor interactions that directly mediate platelet aggregation.
配体诱导结合位点（LIBS）是糖蛋白（GP）IIb-IIIa的新抗原区域，当该受体与配体纤维蛋白原或配体识别序列（RGDS）相互作用时暴露出来。LIBS被认为有助于受体占据后的事件，如全面的血小板聚集、与胶原蛋白的粘附以及凝块回缩。本研究考察了GPIIIa LIBS在配体特异性方面的诱导需求。通过使用抗LIBS D3，我们报告这种复合物激活抗体可诱导纤维蛋白原和血管性血友病因子与完整血小板上的GPIIb-IIIa结合。通过流式细胞术分析和血小板聚集试验检测结合的配体。这些结合的配体增加了D3结合位点的数量，并改变了D3对血小板上GPIIb-IIIa的亲和力。相比之下，D3对血小板GPIIb-IIIa的激活并未增加另一种含RGD的配体玻连蛋白的结合。此外，凝血酶刺激的血小板上结合的玻连蛋白并未导致D3 LIBS表位的表达。我们得出结论，在没有血小板激活的情况下直接激活GPIIb-IIIa会导致选择性配体相互作用，并且D3 LIBS的诱导需要多价配体纤维蛋白原或血管性血友病因子的结合。因此，D3识别的GPIIIa区域可能是配体-受体相互作用中直接介导血小板聚集的重要调节结构域。
