Identification and characterisation of tertiary lymphoid organs in human type 1 diabetes

AIMS/HYPOTHESIS

We and others previously reported the presence of tertiary lymphoid organs (TLOs) in the pancreas of NOD mice, where they play a role in the development of type 1 diabetes. Our aims here are to investigate whether TLOs are present in the pancreas of individuals with type 1 diabetes and to characterise their distinctive features, in comparison with TLOs present in NOD mouse pancreases, in order to interpret their functional significance.

METHODS

Using immunofluorescence confocal microscopy, we examined the extracellular matrix (ECM) and cellular constituents of pancreatic TLOs from individuals with ongoing islet autoimmunity in three distinct clinical settings of type 1 diabetes: at risk of diabetes; at/after diagnosis; and in the transplanted pancreas with recurrent diabetes. Comparisons were made with TLOs from 14-week-old NOD mice, which contain islets exhibiting mild to heavy leucocyte infiltration. We determined the frequency of the TLOs in human type 1diabetes with insulitis and investigated the presence of TLOs in relation to age of onset, disease duration and disease severity.

RESULTS

TLOs were identified in preclinical and clinical settings of human type 1 diabetes. The main characteristics of these TLOs, including the cellular and ECM composition of reticular fibres (RFs), the presence of high endothelial venules and immune cell subtypes detected, were similar to those observed for TLOs from NOD mouse pancreases. Among 21 donors with clinical type 1 diabetes who exhibited insulitis, 12 had TLOs and had developed disease at younger age compared with those lacking TLOs. Compartmentalised TLOs with distinct T cell and B cell zones were detected in donors with short disease duration. Overall, TLOs were mainly associated with insulin-containing islets and their frequency decreased with increasing severity of beta cell loss. Parallel studies in NOD mice further revealed some differences in so far as regulatory T cells were essentially absent from human pancreatic TLOs and CCL21 was not associated with RFs.

CONCLUSIONS/INTERPRETATION

We demonstrate a novel feature of pancreas pathology in type 1 diabetes. TLOs represent a potential site of autoreactive effector T cell generation in islet autoimmunity and our data from mouse and human tissues suggest that they disappear once the destructive process has run its course. Thus, TLOs may be important for type 1 diabetes progression.

T cell and reticular network co-dependence in HIV infection

Fibroblastic reticular cells (FRC) are arranged on a network in the T cell zone of lymph nodes, forming a scaffold for T cell migration, and providing survival factors, especially interleukin-7 (IL-7). Conversely, CD4(+) T cells are the major producers of lymphotoxin-β (LT-β), necessary for the construction and maintenance of the FRC network. This interdependence creates the possibility of a vicious cycle, perpetuating loss of both FRC and T cells. Furthermore, evidence that HIV infection is responsible for collagenation of the network suggests that long term loss of network function might be responsible for the attenuated recovery in T cell count seen in HIV patients undergoing antiretroviral therapy (ART). We present computational and mathematical models of this interaction mechanism and subsequent naive CD4(+) T-cell depletion in which (1) collagen deposition impedes access of naive T cells to IL-7 on the FRC and loss of IL-7 production by loss of FRC network itself, leading to the depletion of naive T cells through increased apoptosis; and (2) depletion of naive T cells as the source of LT-β on which the FRC depend for survival leads to loss of the network, thereby amplifying and perpetuating the cycle of depletion of both naive T cells and stromal cells. Our computational model explicitly includes an FRC network and its cytokine exchange with a heterogeneous T-cell population. We also derive lumped models, in terms of partial differential equations and reduced to ordinary differential equations, that provide additional insight into the mechanisms at work. The central conclusions are that (1) damage to the reticular network, caused by HIV infection is a plausible mechanism for attenuated recovery post-ART; (2) within this, the production of T cell survival factors by FRCs may be the key rate-limiting step; and (3) the methods of model reduction and analysis presented are useful for both immunological studies and other contexts in which agent-based models are severely limited by computational cost.

Essential role of TNF-alpha in development of spleen fibroblastic reticular cells

TNF-alpha plays an important role in the development of secondary lymphoid tissues. Earlier studies showed that fibroblastic reticular cells express TNF-alpha receptor, suggesting that TNF-alpha may affect the development of FRCs. To test this, we analyzed the development and function of FRCs in wild-type or TNF-alpha knockout mice. We found that GP38 expression was down-regulated in the spleen of TNF-alpha knockout mice. Chemokines, mainly secreted by GP38(+) FRCs, were also down-regulated. Additionally, we found that absence of TNF-alpha decreased the homing ability to direct T cells to the spleen. However, absence of TNF-alpha did not affect the development of lymph nodes FRCs. These data reveal that TNF-alpha plays an important role in the development of spleen FRCs. Absence of TNF-alpha could cause abnormality of spleen FRCs, thereby weakening the homing ability of T cells to localize to the spleen T cell zone.

Fibroblastic reticular cells provide a supportive niche for lymph node-resident macrophages

The lymph node (LN) is home to resident macrophage populations that are essential for immune function and homeostasis, but key factors controlling this niche are undefined. Here, we show that fibroblastic reticular cells (FRCs) are an essential component of the LN macrophage niche. Genetic ablation of FRCs caused rapid loss of macrophages and monocytes from LNs across two in vivo models. Macrophages co-localized with FRCs in human LNs, and murine single-cell RNA-sequencing revealed that FRC subsets broadly expressed master macrophage regulator CSF1. Functional assays containing purified FRCs and monocytes showed that CSF1R signaling was sufficient to support macrophage development. These effects were conserved between mouse and human systems. These data indicate an important role for FRCs in maintaining the LN parenchymal macrophage niche.

Microenvironment Matters: Unique Conditions Within Gut-Draining Lymph Nodes Favor Efficient De Novo Induction of Regulatory T Cells

The gastrointestinal tract constitutes the largest surface of the body and thus has developed multitude mechanisms to either prevent pathogen entry or to efficiently eliminate invading pathogens. At the same time, the gastrointestinal system has to avoid unwanted immune responses against self and harmless nonself antigens, such as nutrients and commensal microbiota. Therefore, it is somewhat not unexpected that the gastrointestinal mucosa serves as the largest repository of immune cells throughout the body, harboring both potent pro- as well as anti-inflammatory properties. One additional key element of this regulatory machinery is created by trillions of symbiotic commensal bacteria in the gut. The microbiota not only simply contribute to the breakdown of nutrients, but are essential in limiting the expansion of pathogens, directing the development of the intestinal immune system, and establishing mucosal tolerance by fostering the induction of regulatory T cells (Tregs). In this review, we will discuss our current understanding about the microenvironmental factors fostering the de novo generation of Tregs within the gastrointestinal immune system, focusing on unique properties of antigen-presenting cells, tolerogenic cytokines, commensal-derived metabolites and the contribution of lymph node stromal cells.

Graph Theory-Based Analysis of the Lymph Node Fibroblastic Reticular Cell Network

Secondary lymphoid organs have developed segregated niches that are able to initiate and maintain effective immune responses. Such global organization requires tight control of diverse cellular components, specifically those that regulate lymphocyte trafficking. Fibroblastic reticular cells (FRCs) form a densely interconnected network in lymph nodes and provide key factors necessary for T cell migration and retention, and foster subsequent interactions between T cells and dendritic cells. Development of integrative systems biology approaches has made it possible to elucidate this multilevel complexity of the immune system. Here, we present a graph theory-based analysis of the FRC network in murine lymph nodes, where generation of the network topology is performed using high-resolution confocal microscopy and 3D reconstruction. This approach facilitates the analysis of physical cell-to-cell connectivity, and estimation of topological robustness and global behavior of the network when it is subjected to perturbation in silico.

3D analysis of morphological alterations of the fibroblastic reticular cells in reactive and neoplastic human lymph nodes

Histopathological methods based on 2 μm thin sections are routinely used in pathological anatomical diagnosis. Many medical disciplines already rely on a 3D representation, regarding visualization and imaging techniques. Pathology in particular uses different tissue visualizations to make the final diagnosis. Thereby, a standard 2D histological section only represents a flat snapshot of a three-dimensional complex cell system. Despite that, 3D cell analysis is not yet standardly used in clinical routine. This work used 3D analysis systems to investigate the morphological alterations of the fibroblastic reticular cell network inside human lymph nodes during neoplastic transformation and evaluates the added value of 3D visualizations in tissue interpretation. We investigated the surface and volume quotient, cell cross-linking and percentage cell volume of the fibroblastic reticular cell (FRC) network inside Lymphadenopathy (follicular hyperplasia) (LAD), Follicular Lymphoma Grade 1 (FL1), Nodular Sclerosis classical Hodgkin Lymphoma (NScHL) and Angioimmunoblastic T-Cell Lymphoma (AITL). We found that the average quotient of LAD and FL1 differed from those of NScHL and AITL, indicating that the surface and volume quotient changes in the course of neoplastic transformation. This is probably due to an increased network convolution, while the total cell volume remains the same at about 2%. In conclusion, this paper describes the tumor-related morphological changes of the FRC network, which would have been difficult to achieve without the use of 3D analysis systems.

Cytokeratin-positive interstitial reticulum cell (CIRC) tumor in the lymph node: a case report of the transformation from the epithelioid cell type to the spindle cell type

Background

Cytokeratin-positive interstitial reticulum cells (CIRCs), which are a subgroup of fibroblastic reticular cells (FRCs), are known to be present in the lymph nodes. There have been only a few cases of tumors derived from CIRCs.

Case presentation

We have reported a new case involving a CIRC tumor in a 75-year-old man and reviewed the literature. The resected mediastinal lymph nodes showed epithelial-like proliferation of large atypical round and polygonal epithelioid cells. The tumor cells expressed CK8, CK18, CAM5.2, AE1/AE3, epithelial membrane antigen, vimentin, fascin, and some FRC markers, which is consistent with the diagnosis of a CIRC tumor. Following chemotherapy, the CIRC tumor was observed to have responded very well and became difficult to confirm on imaging, but a small cell lung carcinoma developed 12 months later. Chemoradiotherapy was performed, but the patient passed away 29 months after the initial diagnosis. The autopsy revealed the recurrence of the CIRC tumor, residual small cell lung carcinoma, and a very small latent carcinoma of the prostate. The relapsed CIRC tumor cells had a spindle shape; they were highly pleomorphic and had invaded the superior vena cava.

Conclusion

We first reported autopsy findings of CIRC tumors and demonstrated the transformation of the tumor from the epithelioid cell type to the spindle cell type.

Immune function and dysfunction are determined by lymphoid tissue efficacy

Lymphoid tissue returns to a steady state once each immune response is resolved, and although this occurs multiple times throughout life, its structural integrity and functionality remain unaffected. Stromal cells orchestrate cellular interactions within lymphoid tissue, and any changes to the microenvironment can have detrimental outcomes and drive disease. A breakdown in lymphoid tissue homeostasis can lead to a loss of tissue structure and function that can cause aberrant immune responses. This Review highlights recent advances in our understanding of lymphoid tissue function and remodelling in adaptive immunity and in disease states. We discuss the functional role of lymphoid tissue in disease progression and explore the changes to lymphoid tissue structure and function driven by infection, chronic inflammatory conditions and cancer. Understanding the role of lymphoid tissues in immune responses to a wide range of pathologies allows us to take a fuller systemic view of disease progression.

COX-2 expression in stromal fibroblasts self-limits their numbers in lymph node inflammatory responses

We previously reported the expression of cyclooxygenase (COX)-2 in draining lymph nodes during carrageenin-induced pleurisy of rats. Here, we analyzed histological and immunohistochemical characteristics of COX-2-expressing cells. After carrageenin administration into the pleural cavity of rats, parathymic lymph nodes were enlarged beginning at 8h and peaking from 24 to 48h. Lymphatic follicles disappeared 16h after injection, and numerous macrophages and fibroblasts were observed in the cortical region. COX-2-expressing cells in the cortical region showed characteristic dendritic processes from 16 to 48h and primarily co-localized with stromal fibroblastic reticular cell markers, α-smooth muscle actin (α-SMA), and desmin. Expression of α-SMA increased following COX-2 expression. Nimesulide, a COX-2 inhibitor, increased the dendritic processes of COX-2-expressing cells as well as expression of both COX-2 and α-SMA. These results suggest that COX-2-expressing cells may be stromal fibroblastic cells, which negatively self-regulate their proliferation and modulate tissue remodeling of draining lymph nodes at inflammatory sites.

TNS4 promotes lymph node metastasis of gastric cancer by interacting with integrin Β1 and inducing the activation of fibroblastic reticular cell

Lymph node (LN) metastasis of gastric cancer (GC) is one of the important pathways of GC metastasis, indicating the clinical staging and prognosis of patients. To investigate the underlying mechanism during the process of GC-induced LN metastasis, 7 pairs of GC tissues, paracancerous (PC) tissues, GC-positive LN (LN.P) and GC-negative LN (LN.N) tissues from GC patients with homogeneity were selected for RNA sequencing (RNA-seq) analysis. Tensin 4 (TNS4) was screened out and found to be significantly upregulated in LN.P tissues and closely related with the characteristics of GC. In vitro and in vivo experiments demonstrated that knockdown of TNS4 could significantly inhibit LN metastasis of GC cells and activation of fibroblastic reticular cells (FRCs) in LNs, thus inhibiting LN expansion induced by tumor cell invasion. Moreover, TNS4 was found to be interacted with integrin beta 1 (ITGB1) on FRCs, thereby affecting the binding of transforming growth factor β1 (TGF-β1) to ITGB1 and subsequently regulating downstream signaling molecules, and supporting the GC cell-induced LN metastasis.

An Organotypic Human Lymph Node Model Reveals the Importance of Fibroblastic Reticular Cells for Dendritic Cell Function

BACKGROUND

Human lymph node (HuLN) models have emerged with invaluable potential for immunological research and therapeutic application given their fundamental role in human health and disease. While fibroblastic reticular cells (FRCs) are instrumental to HuLN functioning, their inclusion and recognition of importance for organotypic in vitro lymphoid models remain limited.

METHODS

Here, we established an in vitro three-dimensional (3D) model in a collagen-fibrin hydrogel with primary FRCs and a dendritic cell (DC) cell line (MUTZ-3 DC). To study and characterise the cellular interactions seen in this 3D FRC-DC organotypic model compared to the native HuLN; flow cytometry, immunohistochemistry, immunofluorescence and cytokine/chemokine analysis were performed.

RESULTS

FRCs were pivotal for survival, proliferation and localisation of MUTZ-3 DCs. Additionally, we found that CD1a expression was absent on MUTZ-3 DCs that developed in the presence of FRCs during cytokine-induced MUTZ-3 DC differentiation, which was also seen with primary monocyte-derived DCs (moDCs). This phenotype resembled HuLN-resident DCs, which we detected in primary HuLNs, and these CD1a- MUTZ-3 DCs induced T cell proliferation within a mixed leukocyte reaction (MLR), indicating a functional DC status. FRCs expressed podoplanin (PDPN), CD90 (Thy-1), CD146 (MCAM) and Gremlin-1, thereby resembling the DC supporting stromal cell subset identified in HuLNs.

CONCLUSION

This 3D FRC-DC organotypic model highlights the influence and importance of FRCs for DC functioning in a more realistic HuLN microenvironment. As such, this work provides a starting point for the development of an in vitro HuLN.

Role of SIRPα in Homeostatic Regulation of T Cells and Fibroblastic Reticular Cells in the Spleen

Signal regulatory protein α (SIRPα), is an immunoglobulin superfamily protein that is predominantly expressed in macrophages and dendritic cells (DCs), especially CD4+ conventional DCs (cDCs). In this study, we demonstrated that, in addition to the reduced number of CD4+ cDCs, the number of T cells was significantly decreased in the spleen of Sirpa-/- mice, in which full-length of SIRPα protein was systemically ablated. The size of the T cell zone was markedly reduced in the spleen of Sirpa-/- mice. In addition, Sirpa-/- mice revealed a marked reduction of CCL19, CCL21, and IL-7 expression, which are thought to be important for homeostasis of T cells in the spleen. Consistently, the abundance of fibroblastic reticular cells (FRCs), a subset of stromal cells in the T cell zone, was markedly reduced in the spleen of Sirpa-/- mice compared with Sirpaf/f mice. Moreover, we demonstrated that the mRNA expression of Lymphotoxin (LT) α, LTβ, and LIGHT was significantly reduced in the spleen of Sirpa-/- mice. These data thus suggest that SIRPα is essential for steady-state homeostasis of T cells and FRCs in the spleen.

Isolation and Analysis of Stromal Cell Populations from Mouse Lymph Nodes

Our protocol describes a simple procedure for isolating stromal cells from lymph nodes (LN). LN are disrupted then enzymatically digested with collagenase and dispase to produce a single cell suspension that can be stained with fluorescently labelled antibodies and analysed by flow cytometry. This protocol will enable identification of fibroblastic reticular cells (FRC), lymphatic endothelial cells (LEC), blood endothelial cells (BEC) as PNAd⁺ BEC that form LN high endothelial venules (HEV). This method can be applied to examine LN stromal cell responses during inflammatory events induced by infections or immunologic adjuvants and to subset most leukocytes found in LN.

Unravelling the contribution of lymph node fibroblasts to vaccine responses

Vaccination is one of the most effective medical interventions, saving millions of lives and reducing the morbidity of infections across the lifespan, from infancy to older age. The generation of plasma cells and memory B cells that produce high affinity class switched antibodies is central to this protection, and these cells are the ultimate output of the germinal centre response. Optimal germinal centre responses require different immune cells to interact with one another in the right place and at the right time and this delicate cellular ballet is coordinated by a network of interconnected stromal cells. In this review we will discuss the various types of lymphoid stromal cells and how they coordinate immune cell homeostasis, the induction and maintenance of the germinal centre response, and how this is disorganised in older bodies.