Ontogeny and functional characterization of splenic fibroblastic reticular cells (FRCs) and their mesenchymal precursors during homeostasis, immune-activation and infection

次级淋巴器官（SLO），如脾脏，为免疫反应的发展和控制提供了专门的微环境小生境。被称为成纤维细胞网状细胞（FRC）的特定间充质基质细胞产生不同的区室，其允许例如T细胞与树突细胞的高效相互作用。重要的是，FRC不仅仅是简单的支架构建细胞;这些细胞积极参与诱导和塑造先天性和适应性免疫反应。我们自己的初步数据表明，脾白色髓的结构和功能完全取决于CCL 19阳性FRC在成年期和/或其推定的祖细胞（即间充质淋巴组织组织形成细胞（mLTO））接受的光生素β受体（LTbR）信号。在我们现有的合作活动的延续，我们已经开发出一种新的诱导谱系示踪模型，允许在体内的脾FRC和它们的祖细胞的遗传标记，从而有利于阐明它们的分化途径在整个脾脏发育。此外，该模型系统提供了手段，用于识别和表征的分子机制参与维持脾脏结构和免疫能力在成年生活。因此，结合我们已经建立的细胞类型特异性LTbR功能丧失的实验模型，我们将能够解决LTbR信号传导对成人脾FRC及其推定的胚胎祖细胞的分化和功能的时间要求。最后，使用一个实验模型，促进细胞类型特异性激活LTbR表达在一个及时的控制方式，我们将测试的假设是否FRC限制性LTbR表达在一个特定的时间窗口是足够的适当的白色纸浆的形成和功能在胚胎生命。此外，我们将阐明的要求，及时控制LTbR激活在成年生活中，以保持区室化和功能的脾白色髓。我们提出的目标是基于我们各自的专业知识，并继续我们成功的合作活动。更具体地说，它们被设计用于对脾FRC进行分子表征，并剖析脾FRC与其他脾基质细胞的谱系关系，例如它们在胚胎发育期间从mLTO前体分化。此外，我们将能够识别和功能特性的细胞和分子机制，通过该机制，LTbR表达的FRC参与维持淋巴器官的完整性和免疫能力在成人脾脏，即它们的生态作用，在脾脏微环境中的免疫稳态，激活和感染。

Secondary lymphatic organs (SLOs) such as the spleen provide specialized microenvironmental niches for the development and control of immune responses. Particular mesenchymal stromal cells known as fibroblastic reticular cells (FRCs) generate distinct compartments that permit, for example, highly efficient interaction of T cells with dendritic cells. Importantly, FRCs are more than simple scaffold-building cells; these cells actively participate in inducing and shaping innate and adaptive immune responses. Our own preliminary data demonstrate that the structure and function of the splenic white pulp exclusively depends on lymphotoxin-beta-receptor (LTbR) signaling received by CCL19 positive FRCs during adult life and/or their putative progenitors, i.e. mesenchymal lymphoid tissue organizer cells (mLTOs). In continuation of our existing collaborative activities, we have developed a novel inducible lineage tracing model that permits genetic tagging of splenic FRCs and their progenitors in vivo and will thus facilitate the elucidation of their differentiation pathways throughout spleen development. In addition, this model system provides means for the identification and characterization of molecular mechanisms involved in the maintenance of splenic structure and immune-competence during adult life. Thus, in combination with our already established experimental model of cell type-specific loss of LTbR function, we will be able to resolve the temporal requirement of LTbR signaling for differentiation and function of adult splenic FRCs and their putative progenitors in the embryo. Finally, using an experimental model that facilitates cell type specific re-activation of LTbR expression in a timely controlled manner, we will test the hypothesis whether FRC-restricted LTbR expression within a specific time window is sufficient for proper white pulp formation and function during embryonic life. Furthermore, we will elucidate the requirements for a timely controlled LTbR activation during adult life in order to maintain compartmentalization and function of the splenic white pulp. Our proposed objectives are based on our individual expertise and present the continuation of our successful collaborative activities. More specifically, they are designed to molecularly characterize splenic FRCs and to dissect lineage relationship of splenic FRCs with other splenic stromal cells, e.g. their differentiation from mLTO precursors during embryonic development. Moreover, we will be able to identify and functionally characterize the cellular and molecular mechanisms through which LTbR expressing FRCs are involved in the maintenance of lymphoid organ integrity and immune-competence in the adult spleen, i.e. their ecological role in the splenic micro-environment during immune homeostasis, activation and infection.