Examining Immune Circuits Responsible for Anamnestic RBC Alloimmunization

摘要：之前的同种异体免疫会使患者面临以下情况下形成记忆同种抗体的风险 同种异体抗原再次暴露可导致红细胞加速清除并导致潜在的致命延迟 溶血性输血反应(DHTR)。无法预防DHTR在很大程度上源于根本上的缺乏 对支配记忆性RBC同种异体抗体应答的关键免疫途径的理解 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 记忆同种异体抗体的形成。我们的中心假设是记忆性红细胞同种异体抗体的形成 通过不同的Toll样受体(TLR)，桥接通道树突状细胞(DC)和滤泡(FO)B细胞- 依赖途径，从根本上不同于主要的红细胞同种异体免疫。我们的假设是公式化的 根据我们的发现，与需要边缘带(MZ)B细胞的初始红细胞同种异体免疫不同， MZ B细胞不是形成记忆同种异体抗体所必需的，但对于以下早期启动事件是必需的 发生在最初的红细胞同种异体抗原暴露之后。除了MZ B细胞要求的差异外，虽然最初 同种异体抗体的形成不依赖于CD4T细胞(TI)，在RBC再感染后观察到同种异体抗体水平的升高 暴露完全依赖于CD4T细胞(TD)。此外，虽然T滤泡辅助细胞(TFH)和卵泡 (FO)B细胞不是初始同种抗体形成所必需的，初始RBC输注确实会增加TFH和FO B细胞编号。重新输血还可增加33D1+DC的激活和趋化因子受体的表达。这些 结果表明，初始RBC输注通过产生不同的同种异体抗原特异性TFH和 在RBC同种异体抗原再次暴露后，可被33D1+DC激活的Fo B细胞群 不依赖于MZ B细胞。此外，虽然I型干扰素(IFNab)是主要同种异体抗体所必需的 形成，TLR信号对于最初的同种异体抗体的形成是不必要的，但对于记忆性是必需的 同种异体抗体的形成。鉴于MZ B细胞能够直接激活CD4T细胞并将抗原输送到 B细胞滤泡，我们的数据表明，最初的启动事件需要MZ B细胞介导的CD4T细胞和FO B细胞 通过依赖IFNab的进程进行开发。然而，随着记忆同种异体抗体的形成 通过MZ B细胞非依赖的途径，DC也可以将抗原运输到B细胞并直接激活CD4 T细胞，DC可能通过TLR依赖的途径协调记忆同种异体抗体的形成。为了测试 在这一假说中，我们将追求以下具体目标：具体目标1：确定MZ B细胞和 IFNab在CD4T细胞和FO B细胞发育中所需的后续记忆 同种异体抗体反应。具体目标2：确定TLRs和发展中国家在制定可持续发展战略方面的作用 RBC同种异体抗原再暴露后的记忆同种抗体反应。成功完成这些任务 AIMS将定义调节记忆同种异体抗体反应的关键因素，并在这样做的过程中提供重要的 防止导致DHTRs的同种免疫的框架。

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.