B cell responses in heparin-induced thrombocytopenia

肝素诱导的血小板减少症（HIT）可能是最常见的药物诱导的免疫性疾病， 可导致破坏性或致命的动脉/静脉血栓形成和血栓栓塞。患者IgG抗体， 与肝素复合物中的血小板因子4（PF 4）结合以形成IgG/PF 4/肝素免疫复合物， 是HIT发病机制的核心。这些免疫复合物进而结合血小板表面上的Fc γ Rlla， 诱导血小板活化，导致血小板减少症并促成血栓形成。哈工大展示了 T细胞非依赖性免疫应答的特征，其特征在于抗体的快速发生和下降 和无免疫记忆，以及继发性T细胞依赖性免疫应答的方面， 其特征在于IgG类抗PF 4/肝素抗体的流行和对T细胞的需要。 HIT的这些非典型免疫学特征混淆了我们对该机制的理解， 哪些B细胞参与疾病的免疫发病机制。已知来自B细胞的信号 受体（BCR）是B细胞功能所必需的。BCR信号传导中的一个关键事件是磷脂酶的激活 Cy 2（PLCy 2），其水解膜脂质以产生二酰基甘油（DAG）和肌醇1，4，5- 三磷酸盐（IP 3）。DAG导致涉及蛋白激酶C（PKC）的信号通路的激活， B细胞淋巴瘤10（BcllO）-含有复合物，和蛋白激酶TAK 1。我们之前的目标是 基因破坏研究表明，PLC γ 2/Bcl 10/TAK 1通路对于BCR介导的细胞凋亡至关重要。 抗体生产。此外，用于产生抗小鼠PF 4/肝素HIT抗体的小鼠模型具有 以及可以重现HIT的hFc γ Rlla转基因小鼠。这些模型使它 可以表征对PF 4/肝素复合物的免疫应答的分子方面， 对人类HIT发展至关重要。我们建议使用这些小鼠模型，结合几个 其他基因修饰的小鼠品系，以阐明B细胞如何产生PF 4/肝素特异性抗体 并确定是否操纵PLC γ 2/Bcl 10/TAK 1通路以控制B细胞 抗体的产生可以防止HIT。具体来说，我们将确定1）边缘区的贡献，B1 和记忆B细胞对HIT抗体产生的影响，2）B细胞无反应性的破坏是否有助于 PF 4/肝素特异性B细胞的活化，以及3）PLC γ 2/Bcl 10/TAK 1通路的抑制是否可以 防止HIT。鉴定负责HIT抗体产生的B细胞亚群，确定PF 4 /肝素特异性B细胞被激活，并确定BCR信号通路在HIT抗体中的作用 其生产将为HIT的发病机制提供新的线索，并有助于开发新的预防方法。 相关性（参见说明）： 本研究旨在了解肝素诱导的血小板减少症的原因， 药物引起的危及生命的血液疾病，并预计将确定特定的目标，开发新的 以及控制和预防该病的有效途径。

Heparin-induced thrombocytopenia (HIT) may be the most common drug-induced immune disease, and can result in devastating or fatal arterial/venous thrombosis and thromboembolism. Patient IgG antibodies that bind to platelet factor 4 (PF4) in a complex with heparin to form lgG/PF4/heparin immune complexes are central to the pathogenesis of HIT. These immune complexes, in turn, bind FcyRlla on the platelet surface and induce platelet activation, leading to thrombocytopenia and contributing to thrombosis. HIT exhibits both features of a T ceW-independent immune response, characterized by the rapid onset and decline of antibodies and no immunological memory, as well as aspects of a secondary T ceW-dependent immune response, characterized by the prevalence of the IgG class of anti-PF4/heparin antibodies and a requirement for T cells. These atypical immunological characteristics of HIT have confounded our understanding ofthe mechanism by which B cells contribute to the immune pathogenesis of the disease. It is known that signals from the B cell receptor (BCR) are required for B cell function. A critical event in BCR signaling is activation of phospholipase Cy2 (PLCy2), which hydrolyzes membrane lipids to generate diacylglycerol (DAG) and inositol 1,4,5- trisphosphate (IP3). DAG leads to activation of a signaling pathway that involves protein kinase C (PKC), a B-cell lymphoma 10 (BcllO)-containing complex, and the protein kinase TAK1. Our previous targeted gene-disruption studies have shown that the PLCy2/Bcl10/TAK1 pathway is essential for BCR-mediated antibody production. Moreover, a mouse model for production of anti-mouse PF4/heparin HIT antibodies has been established, as well as hFcyRlla transgenic mice that can recapitulate HIT. These models make it possible to characterize molecular aspects of the immune response to PF4/heparin complexes that are essential to human HIT development. We propose to use these mouse models, in combination with several other genetically-modified mouse strains, to elucidate how B cells produce the PF4/heparin-specific antibodies that cause HIT, and determine whether manipulation of the PLCy2/Bcl10/TAK1 pathway to control B cell antibody production can prevent HIT. Specifically, we will determine 1) the contribution of marginal zone, B1 and memory B cells to HIT antibody production, 2) whether breakdown of B cell anergy contributes to activation of PF4/heparin-specific B cells, and 3) whether inhibition of the PLCy2/Bcl10/TAK1 pathway can prevent HIT. Identifying the B cell subsets responsible for HIT antibody production, determining how PF4 /heparin-specific B cells are activated, and defining the role of the BCR signaling pathway in HIT antibody production will provide new clues to the pathogenesis of HIT and help to develop novel prevention methods. RELEVANCE (See instructions): This study aims to understand the cause of heparin-induced thrombocytopenia, one of the most common drug-induced life-threatening blood diseases, and is expected to identify specific targets for developing novel and effective ways for the control and prevention of this disease.