Regulation of germinal center B cell fate choice by Hedgehog signaling

项目摘要 有效的体液免疫关键取决于生成高水平免疫应答的生发中心（GC）的形成。 亲和力、长寿记忆和浆细胞。在成熟的GC中，组织学上明显的深色（DZ）和浅色 可以观察到一个区域（LZ），后者由基质细胞类型、滤泡树突细胞的存在来定义 （FDCs）。FDC表达高水平的补体和保留免疫复合抗原的Fc受体。在 除了抗原库，LZ还含有大多数T滤泡辅助细胞（Tfh）。GC B细胞 在选择性克隆的周期中经历多轮细胞分裂和基因表达的深刻变化。 扩张.选择具有较高亲和力的B细胞受体（BCR）的LZ GC B细胞涉及抗原 获得、BCR信号传导和Tfh细胞接触的竞争。经过Tfh小组的参与和指导， LZ B细胞经历转录重连，推动它们向DZ移动，在DZ中它们完成一个或多个细胞周期。 更多的细胞分裂通过一个知之甚少的过程，DZ B细胞最终失去了它们的倾向， 然后作为中心细胞迁移回着陆区这种迭代循环过程最终导致 选择性扩增更高亲和力的BCR变体。GC B细胞除了克隆性自我更新外， 上升为长期记忆B细胞和浆细胞谱系，在成熟期间退出GC。的因素 调节再活化的GC B细胞的细胞命运选择还不完全清楚。最近的研究 这与LZ内较强的BCR信号传导促进浆细胞谱系而LZ内较强的BCR信号传导促进浆细胞谱系的想法一致。 在BCR对抗原亲和力较低的GC B细胞中，记忆B细胞的形成占主导地位，推测 是由于不良的抗原获得和呈递导致Tfh细胞参与不足的结果。 然而，FDC衍生因子在GC B细胞命运选择中可能发挥的作用尚未得到研究。 调节再活化的LZ B细胞的细胞命运选择的因素知之甚少。我们审问 影响这些小生境中细胞行为的基质细胞衍生因子是否也在GC中发挥作用。我们 假设Hedgehog信号传导在GC B细胞再活化过程中关键转变中起作用， 影响细胞命运。我们建议定义Hedgehog相关事件和独立事件及其对 GC B细胞谱系分化。这些问题将通过抑制或消除 Hedgehog信号传导和对GC B细胞自我更新或分化起始的影响的检查 到GC中的替代细胞谱系。评估Hedgehog分子影响的拟议实验 信号传导包括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.