Lymph Node Fibroblastic Reticular Cells Construct the Stromal Reticulum via Contact with Lymphocytes

The sophisticated microarchitecture of the lymph node, which is largely supported by a reticular network of fibroblastic reticular cells (FRCs) and extracellular matrix, is essential for immune function. How FRCs form the elaborate network and remodel it in response to lymphocyte activation is not understood. In this work, we established ERTR7+gp38+VCAM-1+ FRC lines and examined the production of the ER-TR7 antigen. Multiple chemokines produced by FRCs induced T cell and dendritic cell chemotaxis and adhesion to the FRC surface. FRCs can secrete the ER-TR7 antigen as an extracellular matrix component to make a reticular meshwork in response to contact with lymphocytes. The formation of the meshwork is induced by stimulation with tumor necrosis factor-α or lymphotoxin-α in combination with agonistic antibody to lymphotoxin-β receptor in a nuclear factor-κB (RelA)–dependent manner. These findings suggest that signals from lymphocytes induce FRCs to form the network that supports the movement and interactions of immune effectors within the lymph node

Organizer-Like Reticular Stromal Cell Layer Common to Adult Secondary Lymphoid Organs

Abstract Mesenchymal stromal cells are crucial components of secondary lymphoid organs (SLOs). Organogenesis of SLOs involves specialized stromal cells, designated lymphoid tissue organizer (LTo) in the embryonic anlagen; in the adult, several distinct stromal lineages construct elaborate tissue architecture and regulate lymphocyte compartmentalization. The relationship between the LTo and adult stromal cells, however, remains unclear, as does the precise number of stromal cell types that constitute mature SLOs are unclear. From mouse lymph nodes, we established a VCAM-1+ICAM-1+MAdCAM-1+ reticular cell line that can produce CXCL13 upon LTβR stimulation and support primary B cell adhesion and migration in vitro. A similar stromal population sharing many characteristics with the LTo, designated marginal reticular cells (MRCs), was found in the outer follicular region immediately underneath the subcapsular sinus of lymph nodes. Moreover, MRCs were commonly observed at particular sites in various SLOs even in Rag2−/− mice, but were not found in ectopic lymphoid tissues, suggesting that MRCs are a developmentally determined element. These findings lead to a comprehensive view of the stromal composition and architecture of SLOs

Novel Targeting to XCR1+ Dendritic Cells Using Allogeneic T Cells for Polytopical Antibody Responses in the Lymph Nodes

Vaccination strategy that induce efficient antibody responses polytopically in most lymph nodes (LNs) against infections has not been established yet. Because donor-specific blood transfusion induces anti-donor class I MHC antibody production in splenectomized rats, we examined the mechanism and significance of this response. Among the donor blood components, T cells were the most efficient immunogens, inducing recipient T cell and B cell proliferative responses not only in the spleen, but also in the peripheral and gut LNs. Donor T cells soon migrated to the splenic T cell area and the LNs, with a temporary significant increase in recipient NK cells. XCR1+ resident dendritic cells (DCs), but not XCR1− DCs, selectively phagocytosed donor class I MHC+ fragments after 1 day. After 1.5 days, both DC subsets formed clusters with recipient CD4+ T cells, which proliferated within these clusters. Inhibition of donor T cell migration or depletion of NK cells by pretreatment with pertussis toxin or anti-asialoGM1 antibody, respectively, significantly suppressed DC phagocytosis and subsequent immune responses. Three allogeneic strains with different NK activities had the same response but with different intensity. Donor T cell proliferation was not required, indicating that the graft vs. host reaction is dispensable. Intravenous transfer of antigen-labeled and mitotic inhibitor-treated allogeneic, but not syngeneic, T cells induced a polytopical antibody response to labeled antigens in the LNs of splenectomized rats. These results demonstrate a novel mechanism of alloresponses polytopically in the secondary lymphoid organs (SLOs) induced by allogeneic T cells. Donor T cells behave as self-migratory antigen ferries to be delivered to resident XCR1+ DCs with negligible commitment of migratory DCs. Allogeneic T cells may be clinically applicable as vaccine vectors for polytopical prophylactic antibody production even in asplenic or hyposplenic individuals

Lymph Node Stromal Cell Subsets

The spatiotemporal regulation of immune responses in the lymph node (LN) depends on its sophisticated tissue architecture, consisting of several subcompartments supported by distinct fibroblastic stromal cells (FSCs). However, the intricate details of stromal structures and associated FSC subsets are not fully understood. Using several gene reporter mice, we sought to discover unrecognized stromal structures and FSCs in the LN. The four previously identified FSC subsets in the cortex are clearly distinguished by the expression pattern of reporters including PDGFRb, CCL21-ser, and CXCL12. Herein, we identified a unique FSC subset expressing both CCL21-ser and CXCL12 in the deep cortex periphery (DCP) that is characterized by preferential B cell localization. This subset was clearly different fromCXCL12highLepRhigh FSCs in themedullary cord, which harbors plasma cells. B cell localization in the DCP was controlled chiefly by CCL21-ser and, to a lesser extent, CXCL12. Moreover, the optimal development of the DCP as well as medulla requires B cells. Together, our findings suggest the presence of a unique microenvironment in the cortex-medulla boundary and offer an advanced view of the multi-layered stromal framework constructed by distinct FSC subsets in the LN

Essential role of CCL21 in establishment of central self-tolerance in T cells

The chemokine receptor CCR7 directs T cell relocation into and within lymphoid organs, including the migration of developing thymocytes into the thymic medulla. However, how three functional CCR7 ligands in mouse, CCL19, CCL21Ser, and CCL21Leu, divide their roles in immune organs is unclear. By producing mice specifically deficient in CCL21Ser, we show that CCL21Ser is essential for the accumulation of positively selected thymocytes in the thymic medulla. CCL21Ser-deficient mice were impaired in the medullary deletion of self-reactive thymocytes and developed autoimmune dacryoadenitis. T cell accumulation in the lymph nodes was also defective. These results indicate a nonredundant role of CCL21Ser in the establishment of selftolerance in T cells in the thymic medulla, and reveal a functional inequality among CCR7 ligands in vivo

Essential role of CCL21 in establishment of central self-tolerance in T cells.

The chemokine receptor CCR7 directs T cell relocation into and within lymphoid organs, including the migration of developing thymocytes into the thymic medulla. However, how three functional CCR7 ligands in mouse, CCL19, CCL21Ser, and CCL21Leu, divide their roles in immune organs is unclear. By producing mice specifically deficient in CCL21Ser, we show that CCL21Ser is essential for the accumulation of positively selected thymocytes in the thymic medulla. CCL21Ser-deficient mice were impaired in the medullary deletion of self-reactive thymocytes and developed autoimmune dacryoadenitis. T cell accumulation in the lymph nodes was also defective. These results indicate a nonredundant role of CCL21Ser in the establishment of self-tolerance in T cells in the thymic medulla, and reveal a functional inequality among CCR7 ligands in vivo

A Distinct Subset of Fibroblastic Stromal Cells Constitutes the Cortex-Medulla Boundary Subcompartment of the Lymph Node

The spatiotemporal regulation of immune responses in the lymph node (LN) depends on its sophisticated tissue architecture, consisting of several subcompartments supported by distinct fibroblastic stromal cells (FSCs). However, the intricate details of stromal structures and associated FSC subsets are not fully understood. Using several gene reporter mice, we sought to discover unrecognized stromal structures and FSCs in the LN. The four previously identified FSC subsets in the cortex are clearly distinguished by the expression pattern of reporters including PDGFRβ, CCL21-ser, and CXCL12. Herein, we identified a unique FSC subset expressing both CCL21-ser and CXCL12 in the deep cortex periphery (DCP) that is characterized by preferential B cell localization. This subset was clearly different from CXCL12highLepRhigh FSCs in the medullary cord, which harbors plasma cells. B cell localization in the DCP was controlled chiefly by CCL21-ser and, to a lesser extent, CXCL12. Moreover, the optimal development of the DCP as well as medulla requires B cells. Together, our findings suggest the presence of a unique microenvironment in the cortex-medulla boundary and offer an advanced view of the multi-layered stromal framework constructed by distinct FSC subsets in the LN