Aldh1a2+ fibroblastic reticular cells regulate lymphocyte recruitment in omental milky spots (stromal fraction of wild-type)
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ABSTRACT: Milky spots, lymphoid clusters present in visceral adipose tissue omentum, play central roles in the regulation of abdominal immunity. Milky spots exhibit hybrid nature between secondary lymph organs and ectopic lymphoid tissues, yet the mechanism of their development and maturation is poorly understood. Here, we identified a subset of fibroblastic reticular cells (FRCs) that are uniquely present in omental milky spots. These FRCs were characterized by the expression of retinoic acid converting enzyme, Aldh1a2, and endothelial cell marker, Tie2, in addition to canonical FRC-associated genes. Diphtheria toxin-mediated ablation of Aldh1a2+ FRCs resulted in the alteration in milky spot structure with a significant reduction in size and cellularity. Mechanistically, Aldh1a2+ FRCs regulated the display of chemokine CXCL12 on high endothelial venules (HEVs), which recruit blood-borne lymphocytes from circulation. We further found that Aldh1a2+ FRCs are required for the maintenance of peritoneal lymphocyte composition. These results illustrate the homeostatic roles of FRCs in the formation of non-classical lymphoid tissues.
Project description:Milky spots, lymphoid clusters present in visceral adipose tissue omentum, play central roles in the regulation of abdominal immunity. Milky spots exhibit hybrid nature between secondary lymph organs and ectopic lymphoid tissues, yet the mechanism of their development and maturation is poorly understood. Here, we identified a subset of fibroblastic reticular cells (FRCs) that are uniquely present in omental milky spots. These FRCs were characterized by the expression of retinoic acid converting enzyme, Aldh1a2, and endothelial cell marker, Tie2, in addition to canonical FRC-associated genes. Diphtheria toxin-mediated ablation of Aldh1a2+ FRCs resulted in the alteration in milky spot structure with a significant reduction in size and cellularity. Mechanistically, Aldh1a2+ FRCs regulated the display of chemokine CXCL12 on high endothelial venules (HEVs), which recruit blood-borne lymphocytes from circulation. We further found that Aldh1a2+ FRCs are required for the maintenance of peritoneal lymphocyte composition. These results illustrate the homeostatic roles of FRCs in the formation of non-classical lymphoid tissues.
Project description:Milky spots, lymphoid clusters present in visceral adipose tissue omentum, play central roles in the regulation of abdominal immunity. Milky spots exhibit hybrid nature between secondary lymph organs and ectopic lymphoid tissues, yet the mechanism of their development and maturation is poorly understood. Here, we identified a subset of fibroblastic reticular cells (FRCs) that are uniquely present in omental milky spots. These FRCs were characterized by the expression of retinoic acid converting enzyme, Aldh1a2, and endothelial cell marker, Tie2, in addition to canonical FRC-associated genes. Diphtheria toxin-mediated ablation of Aldh1a2+ FRCs resulted in the alteration in milky spot structure with a significant reduction in size and cellularity. Mechanistically, Aldh1a2+ FRCs regulated the display of chemokine CXCL12 on high endothelial venules (HEVs), which recruit blood-borne lymphocytes from circulation. We further found that Aldh1a2+ FRCs are required for the maintenance of peritoneal lymphocyte composition. These results illustrate the homeostatic roles of FRCs in the formation of non-classical lymphoid tissues.
Project description:Peyer`s patches (PP) are underpinned by a dense network of FRCs. To elaborate the subset composition and topological organization of PP FRCs, we employed well-characterized Ccl19-Cre and Col6a1-Cre mouse models that permit FRC targeting in secondary lymphoid organs. To define PP FRC subsets and their relation to the observed FRC lineages, we isolated fibroblasts from Col6a1Eyfp and Ccl19Eyfp PPs and performed droplet-based single cell transcriptomics analysis. Taken together, the molecular definition of the PP FRC landscape reveals two FRC lineages furnishing distinct microenvironmental niches.
Project description:Immune protection of the body cavities depends on the swift activation of innate and adaptive immune responses in non-classical secondary lymphoid organs known as fat-associated lymphoid clusters (FALCs). While it is well-established that fibroblastic reticular cells (FRCs) are an integral component of the immune-stimulating infrastructure of lymph nodes and other classical secondary lymphoid organs, it has remained elusive whether and how FRCs in FALCs contribute to peritoneal immunity. Using FRC-specific gene targeting, we found that FALCs are underpinned by an elaborated FRC network and that initiation of peritoneal immunity was governed through FRC activation via MyD88-dependent innate immunological sensing. FRC-specific ablation of Myd88 expression blocked recruitment of inflammatory monocytes into FALCs and subsequent CD4+ T cell-dependent B-cell activation. Moreover, containment of Salmonella infection was compromised in conditionally Myd88-deficient mice indicating that FRCs in FALCs function as initial checkpoint in the orchestration of protective immune responses in the peritoneal cavity.
Project description:Fibroblastic reticular cells (FRCs) actively support secondary lymphoid organ (SLO) architecture. They regulate innate and adaptive immunity by compartmentalizing immune cells in specialized niches, and tightly interacting with them. The phenotypic and functional diversity of FRCs in human SLOs remains largely uncharacterized. We performed a comprehensive profiling of FRCs by single-cell RNA sequencing on human tonsils and lymph nodes. We provide the first complete description of the tonsillar CD45-negative compartment. We identified and validated in tonsil, a population of follicular dendritic cells restricted to the mantle zone and discovered two CCL21-negative FRC subsets intermingling with T-cell zone reticular cells in the extrafollicular space. We also identified podoplanin-positive epithelial cells as a potential plasma cell (PC) niche. We found two levels of FRC-associated diversity: i) tissue-specific subsets; ii) shared subsets with tissue-specific gene signatures. These findings shed new light on the role of FRCs in supporting SLO-specific immune responses.
Project description:T lymphocytes can efficiently counteract the growth of tumors within the tumor microenvironment. Specialized immune-interacting fibroblasts, termed fibroblastic reticular cells (FRC) are responsible for the formation of specialized niches promoting immune cell activation in secondary lymphoid organs and originate from embryonic progenitors. FRCs have also been identified in tertiary lymphoid structures (TLS) in tumor tissues. However, the identity and differentiation of TLS-associated FRC subsets that promote intra-tumoral T cell activity have remained unexplored. Here, we employed single cell RNA-sequencing of fibroblasts and immune cells, sampled from subpleural margin, central margin and unaffected lung tissue in non small cell lung cancer (NSCLC), demonstrating the formation of specific tumor T cell environments (TTEs) underpinned by CCL19-expressing FRCs. We detected tumor-specific FRC subsets namely CCL19-expressing TRCs and perivascular reticular cells (PRCs) interacting with intratumoral T cells, and thus regulating FRC differentiation and T cell activation. Our results highlight a remarkable functionality of FRCs to efficiently determine protective antitumoral T cell responses in NSCLC.
Project description:Lymphoid clusters in visceral adipose tissue omentum, known as milky spots, play a central role in the immunological defense in the abdomen. Milky spots exhibit hybrid nature between secondary lymph organs and ectopic lymphoid tissues, yet their development and maturation mechanisms are poorly understood. Here, we identified a subset of fibroblastic reticular cells (FRCs) that are uniquely present in omental milky spots. These FRCs were characterized by the expression of retinoic acid-converting enzyme, Aldh1a2, and endothelial cell marker, Tie2, in addition to canonical FRC-associated genes. Diphtheria toxin-mediated ablation of Aldh1a2+ FRCs resulted in the alteration in milky spot structure with a significant reduction in size and cellularity. Mechanistically, Aldh1a2+ FRCs regulated the display of chemokine CXCL12 on high endothelial venules (HEVs), which recruit blood-borne lymphocytes from circulation. We further found that Aldh1a2+ FRCs are required for the maintenance of peritoneal lymphocyte composition. These results illustrate the homeostatic roles of FRCs in the formation of non-classical lymphoid tissues.