Watanabe A, Hato T, Kobayashi Y
First Department of Internal Medicine, School of Medicine, Ehime University, Japan.
Int J Hematol. 1992 Aug;56(1):79-87.
We found that a monoclonal antibody to the glycoprotein (GP) IIb-IIIa complex, PMA4, induces fibrinogen binding to platelets, and we examined the mechanism involved. Affinity chromatography and crossed immunoelectrophoresis showed that PMA4 recognized an epitope on the GPIIb-IIIa complex-specific domain. The binding of 125I-fibrinogen to platelets was induced by PMA4 in a concentration-dependent manner and was blocked by EDTA, RGDS peptides and an anti-GPIIb-IIIa monoclonal antibody, PMA1. Binding of the divalent antibody to the GPIIb-IIIa complex was necessary to induce fibrinogen binding and subsequent platelet aggregation, since Fab fragments, unlike PMA4 IgG and F(ab')2 fragments, did not induce fibrinogen binding or aggregation. The PMA4 IgG induced fibrinogen binding, serotonin secretion, and Ca2+ mobilization, whereas F(ab')2 induced fibrinogen binding only. In addition, F(ab')2-induced fibrinogen binding was not abolished in the presence of aspirin, H-7, a protein kinase C inhibitor, PGE1 or dibutyryl cyclic AMP. These results demonstrate that the binding of PMA4 divalent molecules to the GPIIb-IIIa complex can expose platelet fibrinogen receptors in the absence of the stimulatory effects of intracellular mediators on platelets. Thus, we conclude that the fibrinogen receptors on the GPIIb-IIIa complex can be exposed by direct action of the antibody on the complex molecules.
我们发现，一种针对糖蛋白（GP）IIb-IIIa复合物的单克隆抗体PMA4可诱导纤维蛋白原与血小板结合，我们对其中涉及的机制进行了研究。亲和层析和交叉免疫电泳表明，PMA4识别GPIIb-IIIa复合物特异性结构域上的一个表位。125I标记的纤维蛋白原与血小板的结合由PMA4以浓度依赖的方式诱导，并被EDTA、RGDS肽和抗GPIIb-IIIa单克隆抗体PMA1阻断。二价抗体与GPIIb-IIIa复合物的结合对于诱导纤维蛋白原结合及随后的血小板聚集是必要的，因为Fab片段与PMA4 IgG和F(ab')2片段不同，不会诱导纤维蛋白原结合或聚集。PMA4 IgG诱导纤维蛋白原结合、5-羟色胺分泌和Ca2+动员，而F(ab')2仅诱导纤维蛋白原结合。此外，在阿司匹林、蛋白激酶C抑制剂H-7、前列腺素E1或二丁酰环磷腺苷存在的情况下，F(ab')2诱导的纤维蛋白原结合并未被消除。这些结果表明，在缺乏细胞内介质对血小板的刺激作用时，PMA4二价分子与GPIIb-IIIa复合物的结合可暴露血小板纤维蛋白原受体。因此，我们得出结论，GPIIb-IIIa复合物上的纤维蛋白原受体可通过抗体对复合物分子的直接作用而暴露。
