Regulation of germinal center B cell fate choice by Hedgehog signaling

项目摘要 有效的体液免疫关键依赖于生发中心(GC)的形成，这些生发中心产生高水平的 亲和力、长寿记忆和浆细胞。在成熟的GC中，组织学上明显的暗(DZ)和亮 可观察到带(LZ)，后者由一种基质细胞类型滤泡树突状细胞的存在所定义 (FDDC)。FDC表达高水平的补体和Fc受体，保留免疫复合抗原。在……里面 除抗原库外，LZ还藏有大多数T滤泡辅助细胞(TFH)。GC B细胞 在选择性克隆周期中经历多轮细胞分裂和基因表达的深刻变化 扩张。具有高亲和力B细胞受体(BCR)的LZ GC B细胞的筛选涉及抗原 获取、BCR信号和TFH细胞接触的竞争。在TFH细胞接合和指示之后， LZ B细胞经历转录重新连接，推动它们移动到DZ，在那里它们完成一个或 更多的细胞分裂。通过一个知之甚少的过程，DZ B细胞最终失去了保留的倾向 在该区域内，并作为中心细胞迁移回LZ。这种迭代的循环过程最终导致 选择性扩增亲和力更高的bcr变异体。除了克隆自我更新外，GC B细胞还提供 上升到长期记忆的B细胞和浆细胞谱系，在成熟过程中退出GC。这些因素是 重新激活的GC-B细胞对细胞命运的调控选择还不完全清楚。最近的研究是 与LZ内较强的BCR信号促进浆细胞谱系的想法一致，而LZ内较强的BCR信号促进浆细胞谱系 BCR与抗原亲和力较低的GC B细胞中，记忆B细胞的形成占主导地位，推测 这是由于抗原获取和提呈不佳导致TFH细胞结合不足的结果。 然而，FDC衍生因子在GC B细胞命运选择中可能发挥的作用还没有被研究过。 调节重新激活的LZ B细胞命运选择的因素还知之甚少。我们询问了 基质细胞衍生的因素是否在这些小生境中影响细胞行为也可以在GCs中发挥作用。我们 假设Hedgehog信号在GC B细胞重新激活过程中的关键转变中发挥作用 影响细胞的命运。我们建议定义Hedgehog依赖和独立事件及其对 GC B细胞谱系分化。这些问题将通过抑制或消融 Hedgehog信号及其对GC-B细胞自我更新或分化启动的影响 在GC内有不同的细胞谱系。评估刺猬分子影响的拟议实验 信号转导包括GC B细胞的scRNAseq。

Project Summary Effective humoral immunity critically depends on the formation of germinal centers (GC) that generate high- affinity, long-lived memory and plasma cells. Within mature GCs, histologically distinct dark (DZ) and light zones (LZ) can be observed, the latter defined by the presence of a stromal cell type, follicular dendritic cells (FDCs). FDCs express high levels of complement and Fc receptors that retain immune complexed antigen. In addition to a depot of antigen, the LZ also harbors the majority of T follicular helper cells (Tfh). GC B cells undergo many rounds of cell division and profound shifts in gene expression during cycles of selective clonal expansion. The selection of LZ GC B cells with B cell receptors (BCR) of higher affinity involves antigen acquisition, BCR signaling and competition for Tfh cell contacts. After engagement and instruction by Tfh cells, LZ B cells undergo transcriptional rewiring that propels their movement to the DZ where they complete one or more cell divisions. Through a poorly understood process, DZ B cells eventually lose their propensity to remain within that zone and migrate back to the LZ as centrocytes. This iterative cyclic process ultimately results in the selective expansion of higher affinity BCR variants. In addition to their clonal self-renewal, GC B cells also give rise to long-term memory B cell and plasma cell lineages that exit the GC during maturation. The factors that regulate the cell fate choice of reactivated GC B cells are incompletely understood. Recent studies are consistent with the idea that stronger BCR signaling within the LZ promotes the plasma cell lineage while the formation of memory B cells predominates among GC B cells with BCRs of lower affinity for antigen, presumed to be the result of insufficient engagement of Tfh cells due to poor antigen acquisition and presentation. However, the role that FDC-derived factors might play in GC B cell fate choices have not been examined. The factors that regulate the cell fate choice of reactivated LZ B cells is poorly understood. We questioned whether stromal cell-derived factors influencing cell behavior in those niches could also play a role in GCs. We hypothesize that Hedgehog signaling plays a role in critical transitions during GC B cell re-activation that influence cell fate. We propose to define the Hedgehog dependent and independent events and their impact on GC B cell lineage divergence. These questions will be addressed through the inhibition or ablation of Hedgehog signaling and an examination of the effect on GC B cell self-renewal or the initiation of differentiation to alternative cell lineages within the GCs. Proposed experiments to assess the molecular impact of Hedgehog signaling include scRNAseq of GC B cells.