Shido K, Ahmad G, Hsu L, Kamiyama M
Department of Biology, Seton Hall University, South Orange, N.J. 07079-2689, USA.
J Clin Lab Immunol. 1995;46(1):1-11.
Human platelets express IgG Fc receptors (Fc gamma R). Previously we reported that circulating immune complexes (CIC) inhibited fibrinogen binding to platelet glycoprotein IIb/IIIa complex (GPIIb/IIIa) and that isolated Fc gamma R were recognized by monoclonal antibodies (mAb's) to GPIIb and GPIIIa (J.Lab. Clin. Med. 117:209-217, 1991). In this study, we further characterized the properties of the Fc gamma R and the activity associated with GPIIb/IIIa. Binding of Fc portion of human IgG (Fc) to the platelet Fc gamma R associated with GPIIb/IIIa complex, unlike fibrinogen receptor, did not require divalent cations. The Fc gamma R bound to immobilized immune complex were recognized by mAb's to GPIIb, GPIIIa, GPIIb/IIIa. Preincubation of platelet extract with fibrinogen inhibited the binding of heat-aggregated IgG (HAG) to the extract. Flow cytometry of whole platelets revealed inhibition of mAb binding to GPIIb/IIIa, when platelets were incubated with Fc fragments or HAG. Using platelet extract coated to microtiter plates, similar findings were noted with Fc and HAG. The dissociation of GPIIb/IIIa complex by incubating platelet extract at 37 degrees C in the presence of EDTA caused a marked decrease in the binding of GPIIb and GPIIIa to the immobilized immune complex. Activation of intact platelets with ADP resulted in an increased binding of HAG to the platelets, indicating that an augmented Fc gamma R activity is associated with the activation of GPIIb/IIIa. These results suggest a close relationship of the Fc gamma R activity to the fibrinogen binding site (GPIIb/IIIa complex).
人类血小板表达IgG Fc受体（FcγR）。此前我们报道，循环免疫复合物（CIC）抑制纤维蛋白原与血小板糖蛋白IIb/IIIa复合物（GPIIb/IIIa）的结合，并且分离出的FcγR可被针对GPIIb和GPIIIa的单克隆抗体（mAb）识别（《实验室与临床医学杂志》117:209 - 217, 1991）。在本研究中，我们进一步阐述了FcγR的特性以及与GPIIb/IIIa相关的活性。与纤维蛋白原受体不同，人IgG（Fc）的Fc部分与和GPIIb/IIIa复合物相关的血小板FcγR的结合不需要二价阳离子。与固定化免疫复合物结合的FcγR可被针对GPIIb、GPIIIa、GPIIb/IIIa的mAb识别。血小板提取物与纤维蛋白原预孵育可抑制热聚集IgG（HAG）与提取物的结合。当血小板与Fc片段或HAG孵育时，全血小板的流式细胞术显示mAb与GPIIb/IIIa的结合受到抑制。使用包被在微量滴定板上的血小板提取物，Fc和HAG也有类似发现。在37℃下于EDTA存在的情况下孵育血小板提取物导致GPIIb/IIIa复合物解离，这使得GPIIb和GPIIIa与固定化免疫复合物的结合显著减少。用ADP激活完整血小板会导致HAG与血小板的结合增加，表明增强的FcγR活性与GPIIb/IIIa的激活相关。这些结果提示FcγR活性与纤维蛋白原结合位点（GPIIb/IIIa复合物）密切相关。
