Modeling the spectrum of HIT pathobiology

描述(由申请者提供)：这一小额拨款申请的目标是为肝素诱导的血小板减少症(HIT)的研究开发一种研究方法。HIT是一种血栓前疾病，由抗凝剂肝素过敏反应引起。HIT是由针对血小板蛋白、血小板因子4(PF4)和肝素(H)的抗体引起的。由于PF4/H抗体可以在患者中引发危及生命的血栓并发症，因此对疾病发病机制的实验研究依赖于动物模型。目前已发展了两种不同的动物模型来研究HIT，一种是研究HIT的血栓性并发症(小鼠HIT模型)，另一种是我们实验室建立的研究PF4/H免疫反应的小鼠免疫模型。在R03的应用中，我们建议建立一个完整的小鼠模型来研究人类HIT的发病机制。在初步研究的基础上，我们假设PF4/H抗体的致病性是由循环抗原(PF4/H复合体)、PF4/H抗体和激活的血小板Fc RIIA受体三个因素共同决定的。我们建议使用两种方法中的一种来验证这一假设，这两种方法依赖于Fc RIIA表达(单转基因模型)的存在以及HPF4的表达(双转基因模型)。在第一种方法中，我们将在一个单一的转基因模型(表达HFC RIIA的小鼠)中诱导PF4/H抗体，目的是检测抗原载量、抗体效价和Fc RII表达的影响。在第二种方法中，我们希望用表达人(H)PF4和hFc RIIA的双转基因小鼠来建立人源化的小鼠模型，以检测HPF4水平和hFcR表达对免疫反应和疾病表达的影响。在寻求这一小额研究拨款的过程中，我们希望这些优化的小鼠模型将促进未来对致病HIT抗体潜在进化机制的研究。

DESCRIPTION (provided by applicant): The goal of this small grant application is to develop a research methodology for studies of Heparin-Induced Thrombocytopenia (HIT). HIT is a prothrombotic disorder caused by an allergic response to the anticoagulant drug, heparin. HIT is caused by antibodies directed towards a platelet protein, Platelet Factor 4 (PF4) and heparin (H). Because PF4/H antibodies can elicit life-threatening thrombotic complications in patients, experimental studies of disease pathogenesis have relied on animal models. Two distinct animal models have been developed to study HIT; one model studies thrombotic complications of HIT (murine HIT model) and the other, a murine immunization model developed by our lab to study the PF4/H immune response. In this R03 application, we propose to develop an integrated murine model for studies of human HIT pathogenesis. Based on preliminary studies, we hypothesize that pathogenicity of PF4/H antibodies is determined by the confluence of three factors, circulating antigen (PF4/H complexes), PF4/H Abs and activating platelet Fc RIIA receptors. We propose to test this hypothesis using one of two approaches relying on the presence of Fc RIIA expression (single transgenic model) with or without expression of hPF4 (double transgenic model). In the first approach, we will induce PF4/H antibodies in a single transgenic model (mice expressing hFc RIIA) with the goal of examining effects of antigen load, antibody titer and Fc RII expression. In the second approach, we wish to develop a "humanized" murine model using double transgenic mice expressing human (h)PF4 and hFc RIIA to examine the effects of hPF4 levels and hFcR expression on the immune response and disease expression. In pursuing this small research grant, we hope that these optimized murine models will facilitate future investigations on the mechanisms underlying evolution of pathogenic HIT antibodies.