Immunobiology of GPIIb/IIIa

纤维蛋白原受体拮抗剂(FRAs)是一类很有前途的新型抗血栓药物。然而，到目前为止，在这些药物的临床试验中，0.1-1.0%的治疗患者经历了急性、严重的血小板减少症。虽然临床表现提示免疫病因学，但关于这一点的已发表信息很少。在初步研究中，我们已经获得证据表明，FRA引起的血小板减少是由抗体(Abs)引起的，这种抗体通常是“自然产生的”，识别经FRA治疗的血小板上的GPIIb/IIIa。在这一应用中，我们建议进行研究，以确定这种疾病的发病机制，探索负责任的“天然”抗体的意义，并开发改进的方法来诊断和识别有风险的患者发展这种并发症。发病机制-与FRA诱导的血小板减少相关的抗体将强调以下假设：1)在用阿昔单抗(ReoPro)治疗的患者中导致血小板减少的抗体是针对嵌合abciximab分子中的C末端(人)肽序列和/或鼠序列的，2)在接受配体模拟化合物治疗的患者中使用的抗体是BPII/IIIA上识别的配体结合位点(LIB)。我们将寻求建立一种类似配体的FRAs诱导的小鼠血小板减少的模型，在该模型中可以系统地研究FRA诱导的血小板减少的机制和引起ABS的原因。获得的信息将被用来开发敏感、具体和实用的方法，用于识别能够导致FRA治疗患者血小板减少的abs，并用于预测FRA是否可以安全使用。“天然抗体”(NA)-NA与正常的身体动态平衡和各种免疫紊乱有关。我们建议探索一些相对常见的NA识别配体诱导的GPIIb/IIIa异二聚体构象变化的假设，以表征这些NA与FRA诱导的血小板减少的关系，并确定它们的免疫学来源，它们在血小板中的潜在作用以及它们对输血前保存的血小板质量的影响。B细胞库-我们将利用免疫球蛋白V基因扩增和噬菌体展示技术来确定患者和正常受试者所使用的B细胞库，以产生针对配体占据的GPIIb/IIIa的抗体，并在分子水平上表征NA与病理抗体之间的关系。

Fibrinogen receptor antagonists (FRAs) are a promising new family of anti-thrombotic drugs. However, in clinical trial of these agents conducted to date, 0.1-1.0% of treated patients has experienced acute, severe thrombocytopenia. Although clinical presentation suggests an immunologic etiology, very little published information on this point is available. In preliminary studies, we have obtained evidence that FRA- induced thrombocytopenia is caused by antibodies (abs), often "naturally occurring", that recognize GPIIb/IIIa on platelets treated with an FRA. In this application, we propose studies to characterize the pathogenesis of this disorder, explore the significance of the responsible "natural" antibodies, and develop improved methods for diagnosis and for identifying patients at risk to develop this complication. Pathogenesis-Abs associated with FRA-induced thrombocytopenia will be characterized with emphasis on the following hypotheses: 1) Abs that cause thrombocytopenia in patients treated with abciximab (ReoPro) are specific for C terminal (human) peptide sequences and/or murine sequences in the chimeric abciximab molecule and 2) Abs in patients treated with ligand-mimetic compounds recognized ligand-binding sites (LIBS) on BPII/IIIA. We will seek to develop a murine model of thrombocytopenia induced by ligand-mimetic FRAs in which mechanisms of FRA-induced thrombocytopenia and the origin of the responsible abs can be systematically studied. Information gained will be used to develop sensitive, specific and practical methods for identifying abs capable of causing thrombocytopenia in FRA-treated patients and for predicting whether an FRA can be safely administered. "Natural Antibodies" (NA)-NA have been implicated in normal body homeostasis and in various immune disorders. We propose to explore the hypothesis that some relative common NA recognize ligand-induced conformation changes in the GPIIb/IIIa heterodimer, to characterize the relationship of these NA to FRA-induced thrombocytopenia, and to define their immunologic origin, their potential role in platelet and their effects on the quality of platelets stored prior to transfusion. B cell repertoire- We will utilize immunoglobin V gene amplification and phage display technology to define the B cell repertoire utilized by patients and normal subjects to generate abs specific for ligand-occupied GPIIb/IIIa and to characterize the relationship between NA and pathologic antibodies at a molecular level.