Examining Immune Circuits Responsible for Anamnestic RBC Alloimmunization

总结：既往同种免疫接种使患者处于既往同种抗体形成的风险中， 同种异体抗原再暴露，可导致RBC清除加速，并导致潜在致命的延迟 溶血性输血反应（DHTR）。无法预防DHTR很大程度上源于缺乏一个基本的 了解关于关键免疫途径，管理记忆红细胞同种抗体反应， 驾驶DHTR。我们的长期目标是确定并瞄准调控发展的关键途径， 记忆性同种抗体的形成。我们的中心假设是记忆性红细胞同种抗体的形成 通过不同的toll样受体（TLR）、桥接通道树突细胞（DC）和滤泡（FO）B细胞发生。 依赖途径，从根本上不同于主要的红细胞同种异体免疫。我们的假设是 基于我们的发现，与需要边缘区（MZ）B细胞的初始RBC同种异体免疫不同， MZ B细胞不是记忆性同种抗体形成所必需的，但却是早期引发事件所必需的， 发生在最初的RBC同种异体抗原暴露后。除了MZ B细胞要求的差异外， 同种抗体的形成是CD4 T细胞非依赖性的（TI），在RBC再灌注后观察到同种抗体水平增加， 暴露完全是CD4 T细胞依赖性的（TD）。此外，虽然T滤泡辅助细胞（TFH）和滤泡 (FO)初始同种抗体形成不需要B细胞，初始RBC输注确实增加TFH和FO B细胞数量。回输还增加33D1+ DC活化和趋化因子受体表达。这些 结果表明，最初的红细胞输注通过产生不同的同种异体抗原特异性TFH来启动受体， FO B细胞群在RBC同种异体抗原再暴露后可被33 D1 + DC激活 不依赖于MZ B细胞。此外，虽然I型干扰素（IFNab）是一级同种抗体所必需的， 虽然TLR信号传导对于最初的同种抗体形成是必需的，但对于记忆性抗体形成是必需的。 同种抗体形成。考虑到MZ B细胞直接激活CD4 T细胞并将抗原运输至T细胞的能力， B细胞滤泡，我们的数据表明，初始启动事件需要MZ B细胞介导的CD 4 T细胞和FO B细胞 通过IFNab依赖的过程发展。然而，随着记忆性同种抗体的形成， 通过MZ B细胞非依赖性途径，DC还可以将抗原运输至B细胞并直接激活CD4 T细胞、DC可能通过TLR依赖性途径协调记忆性同种抗体形成。测试 在这个假设中，我们将追求以下具体目标：具体目标1：定义MZ B细胞的作用， IFN α B在CD4 T细胞和FO B细胞的发育中为随后的回忆所需 同种抗体反应具体目标2：明确TLR和DC在肿瘤发生发展中的作用。 RBC同种异体抗原再暴露后的记忆性同种异体抗体应答。成功完成这些 aims将定义调节记忆性同种抗体应答的关键因素，并在此过程中提供重要的 框架，以防止同种异体免疫，导致DHTR。

Summary: Prior alloimmunization places patients at risk for anamnestic alloantibody formation following alloantigen re-exposure that can result in accelerated RBC clearance and lead to a potentially fatal delayed hemolytic transfusion reaction (DHTR). The inability to prevent DHTRs largely stems from a fundamental lack of understanding regarding key immune pathways that govern anamnestic RBC alloantibody responses capable of driving DHTRs. Our long-term goal is to identify and then target critical pathways that regulate the development of anamnestic alloantibody formation. Our central hypothesis is that anamnestic RBC alloantibody formation occurs through a distinct toll-like receptor (TLR), bridging channel dendritic cell (DC) and follicular (FO) B cell- dependent pathway that fundamentally differs from primary RBC alloimmunization. Our hypothesis is formulated on the basis of our discovery that unlike initial RBC alloimmunization, which requires marginal zone (MZ) B cells, MZ B cells are not required for anamnestic alloantibody formation, but are required for early priming events that occur following initial RBC alloantigen exposure. In addition to differences in MZ B cell requirements, while initial alloantibody formation is CD4 T cell independent (TI), increased alloantibody levels observed following RBC re- exposure is entirely CD4 T cell dependent (TD). Furthermore, while T follicular helper cell (TFH) and follicular (FO) B cells are not required for initial alloantibody formation, initial RBC transfusion does increase TFH and FO B cell numbers. Re-transfusion also increases 33D1+ DC activation and chemokine receptor expression. These results suggest that initial RBC transfusion primes recipients by generating distinct alloantigen-specific TFH and FO B cell populations that can, in turn, be activated by 33D1+ DCs following RBC alloantigen re-exposure independent of MZ B cells. In addition, while type I interferons (IFNab) are required for primary alloantibody formation, TLR signaling is dispensable for initial alloantibody development, yet is required for anamnestic alloantibody formation. Given the ability of MZ B cells to directly activate CD4 T cells and traffic antigen to the B cell follicle, our data suggest that initial priming events require MZ B cell-mediated CD4 T cell and FO B cell development through an IFNab-dependent process. However, as anamnestic alloantibody formation occurs through a MZ B cell-independent pathway and DCs can also traffic antigen to B cells and directly activate CD4 T cells, DCs likely orchestrate anamnestic alloantibody formation through a TLR-dependent pathway. To test this hypothesis, we will pursue the following specific aims: Specific Aim 1: Define the role of MZ B cells and IFNab in the development of CD4 T cells and FO B cells required for a subsequent anamnestic alloantibody response. Specific Aim 2: Define the role of TLRs and DCs in the development of an anamnestic alloantibody response following RBC alloantigen re-exposure. Successful completion of these aims will define key factors that regulate anamnestic alloantibody responses and in so doing provide an important framework to prevent alloimmunization that leads to DHTRs.