Functional characterization of CXCL13-producing stromal cells in secondary lymphoid organs
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Date
2017Type
- Doctoral Thesis
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Abstract
Secondary lymphoid organs (SLOs) are central hubs for the interaction of lymphocytes and their efficient activation. The structure and function of SLOs is determined by fibroblastic reticular cells (FRCs), which attract, maintain and activate lymphocytes in SLOs. Three major FRC-subsets can be found in SLOs: T cell-zone FRCs (TRCs) form a dense network in paracortical T cell zones, follicular dendritic cells (FDCs) are located in germinal centers of follicular B cell zones and marginal reticular cells (MRCs) form a cell layer at the margin of follicular and perifollicular areas in lymph nodes (LNs) and the splenic white pulp. FRCs descend from a common precursor that requires lymphotoxin beta receptor (LTbR)-signaling for its differentiation into the respective subsets. Additionally, it has been hypothesized that LTbR-expressing mesenchymal lymphoid tissue organizer (LTo) cells initiate the formation of SLOs after interaction with hematopoietic lymphoid tissue inducer (LTi) cells. Such LTo cells secrete chemokine C-X-C motif ligand 13 (CXCL13) to attract LTi cells and other lymphocytes into the growing primordium. However, the precise identity of CXCL13+ LTo cells and their direct progeny remained elusive. Therefore, the first aim of this work was to generate a novel transgenic mouse model, which targets CXCL13-producing cells and their progeny. We describe the successful generation of the novel transgenic Cxcl13-Cre/tdTomato mouse model, which targets bona fide FRCs in SLOs. Lineage tracing experiments revealed that Cxcl13-Cre/tdTomato-targeted FRCs descent from CXCL13-producing precursor cells and are highly abundant in SLOs. As expected, current CXCL13-production reported by tdTomato expression was restricted to the follicular and perifollicular areas of SLOs and included FDCs and MRCs. To investigate whether presumptive mesenchymal LTo cells are the true LTbR-sensitive LTo cells required for organ formation, we specifically ablated LTbR on CXCL13-producing cells. Surprisingly, the conditional deletion of LTbR did not impact on the development of lymph nodes. In contrast, the formation of the splenic white pulp and Peyerˈs patches was severely impaired.
Besides of a dense network of intestinal fibroblasts in the lamina propria, also solitary intestinal lymphoid tissues (SILT) were targeted in Cxcl13-EYFP mice. The conditional ablation of Ltbr did not impair the development of cryptopatches, but arrested the maturation of SILT structures. Since the Cxcl13-Cre/tdTomato transgene did not allow the specific manipulation of SILT FRC-like cells, we resorted to the previously generated Ccl19-EYFP mouse model to investigate the contribution of FRC-like cells to SILT maturation. Using this model, we demonstrated that CCL19-expressing FRC-like cells are exclusively present in SILT of the lamina propria. Furthermore, we found that FRC-like cells targeted by the Ccl19-Cre transgene are required for the transition of cryptopatches into mature isolated lymphoid follicles (ILFs) and that the ablation of LTbR in these cells abrogated ILF maturation. This was associated with a significant reduction in innate lymphoid cell (ILC) numbers in the intestinal lamina propria and an increased susceptibility to infection with Citrobacter rodentium. Hence, this work describes a novel subset of FRC-like cells in SILT structures, which form a LTbR-dependent niche for ILC homeostasis and contribute to intestinal immunocompetence.
Taken together, this project enabled the generation of a novel transgenic mouse model, which is well-suited to study CXCL13-producing stromal cells in SLOs. Our data demonstrate that CXCL13-expressing cells require LTbR-signaling to initiate organogenesis of the splenic white pulp and Peyerˈs patches, while the development of lymph nodes and cryptopatches is independent of LTbR-signaling on these cells. Even though FRC-like cells in SILT structures are not required for the initial formation of cryptopatches, the maturation of SILT structures and their function is governed by LTbR+ FRC-like cells, highlighting their important role in intestinal immunity. Collectively, our data indicate that distinct LTo populations drive the development of conventional as well as non-conventional SLOs. Show more
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Contributors
Examiner: Kopf, Manfred
Examiner: Ludewig, Burkhard
Examiner: Halin, Cornelia
Examiner: Münz, Christian
Publisher
ETH ZurichSubject
Immunology; Fibroblastic reticular cells; Secondary lymphoid organs; CXCL13; Lymphotoxin beta receptorOrganisational unit
03596 - Kopf, Manfred / Kopf, Manfred
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