Marginal Zone B Cell Regulation of Red Blood Cell Alloimmunization

项目摘要 红细胞输注可诱导同种抗体，使将来难以找到相容的血液 输血，增加不相容输血反应的可能性，并直接增加发病率， 镰状细胞病（SCD）患者的死亡率。经验数据表明，尽管抗原匹配 方案减少RBC同种免疫，目前没有可用的策略完全防止RBC诱导的免疫。 治疗性输血后同种抗体形成。这在一定程度上反映了对以下问题缺乏了解： 负责启动RBC同种异体免疫的关键因素。我们的中心假设是，边缘区（MZ） B细胞代表对RBC同种异体抗原的免疫应答的起始和协调的中心节点， 因此可能是一个可行的免疫学靶点，用于开发新的策略， 也防止RBC同种抗体的产生。我们的假设是根据我们最近的发现提出的 MZ B细胞是临床前模型中RBC同种抗体形成所必需的。作为MZ B细胞可以运输抗原到B细胞滤泡，红细胞同种免疫对MZ B细胞的需求可能反映了 捕获同种异体RBC并随后将其递送至B细胞滤泡，然后抗原底物 由CD4 T滤泡辅助细胞（TFH）用于驱动有效的生发中心反应， 显著同种抗体形成。由于抗原捕获需要B细胞受体结合和MZ B细胞 在任何给定的个体中具有有限的和不同的抗体特异性库，这些数据也 提示红细胞同种异体抗原特异性MZ B细胞前体频率的差异可预测 RBC同种异体抗原暴露后个体产生同种异体抗体的可能性。此外如 Toll样受体（TLR）激动剂可以直接增加MZ B细胞活性，直接参与TLR的条件， 如SCD患者急性胸部综合征（ACS）期间释放的过量氯化血红素，可能会增加 红细胞同种异体免疫的可能性，通过积极影响MZ B细胞功能，因此可以部分解释 SCD患者产生RBC同种抗体的倾向增加。这些初步数据表明， MZ B细胞作为调节RBC同种抗体形成的关键参与者，并在这样做时提供了独特的 有机会确定MZ B细胞在预测和预防RBC同种异体免疫中的作用。完成 为此，项目2将采用临床和临床前研究的互补方法来焊接观察数据 机制研究，以确定MZ B细胞在红细胞同种免疫调节中的作用， 测试以下具体目的：目的1：确定MZ B细胞在RBC同种异体免疫中的作用。目标二： 确定ACS对MZ B细胞和TFH活化的影响。我们认为，成功完成这些 目标不仅能够为RBC的关键方面提供新的机制见解， 同种免疫，但也可能建立一个重要的框架，以制定合理的方法， 预测并最终预防长期输血个体的RBC同种抗体形成。

Project Summary RBC transfusion can induce alloantibodies that can make it difficult to find compatible blood for future transfusions, increase the likelihood of incompatible transfusion reactions, and directly increase morbidity and mortality in patients with sickle cell disease (SCD). Empirical data have shown that although antigen-matching protocols reduce RBC alloimmunization, no currently available strategies completely prevent RBC-induced alloantibody formation following therapeutic transfusion. This in part reflects a lack of understanding regarding key factors responsible for initiating RBC alloimmunization. Our central hypothesis is that marginal zone (MZ) B cells represent a central node in the initiation and orchestration of immune responses to RBC alloantigens, and thus may be a viable immunological target for the development of novel strategies to not only predict, but also prevent RBC alloantibody production. Our hypothesis is formulated on the basis of our recent discovery that MZ B cells are required for the development of RBC alloantibody formation in a pre-clinical model. As MZ B cells can traffic antigen to B cell follicles, the requirement of MZ B cells in RBC alloimmunization may reflect the trapping and subsequent delivery of allogeneic RBCs to B cell follicles, where antigenic substrate is then used by CD4 T follicular helper cells (TFH) to drive effective germinal center reactions responsible for significant alloantibody formation. As antigen trapping requires B cell receptor engagement and MZ B cells possess a restricted and distinct repertoire of antibody specificities in any given individual, these data also suggest that differences in the precursor frequency of RBC alloantigen specific MZ B cells may predict the likelihood that an individual will develop alloantibodies following RBC alloantigen exposure. Furthermore, as toll-like receptor (TLR) agonists can directly increase MZ B cell activity, conditions that directly engage TLRs, such as excess hemin released during acute chest syndrome (ACS) in patients with SCD, may increase the likelihood of RBC alloimmunization by positively impacting MZ B cell function, and therefore may explain in part the increased propensity of patients with SCD to develop RBC alloantibodies. These preliminary data identify MZ B cells as key players in regulating RBC alloantibody formation, and in so doing provide a unique opportunity to define the role of MZ B cells in predicting and preventing RBC alloimmunization. To accomplish this, Project 2 will use a complementary approach of clinical and pre-clinical studies to weld observational data with mechanistic studies in order to define the role of MZ B cells in the regulation of RBC alloimmunization by testing the following specific aims: Aim 1: Define the role of MZ B cells in RBC alloimmunization. Aim 2: Define the impact of ACS on MZ B cell and TFH activation. We believe that successful completion of these aims not only possess the capacity to provide new mechanistic insight into key aspects of RBC alloimmunization, but may also establish an important framework to develop rational approaches designed to prophylactically predict and ultimately prevent RBC alloantibody formation in chronically transfused individuals.