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Secondary lymphoid organs are critical for efficient interaction between innate antigen presenting cells and adaptive lymphocytes in order to start adaptive immune responses. The efficiency by which these cellular subsets meet is highly increased by the orchestrating role of stromal cells within the secondary lymphoid organs. These cells provide cytokines, chemokines and cell surface receptors necessary for survival and guided migration. This increases the likelihood that antigen specific adaptive immune responses occur. Already from initial formation of secondary lymphoid organs, the interaction of immune cells with stromal cells is crucial and this interaction continues during immune activation. With the recent discovery of many stromal cell subsets new immune micro-niches with specific functions that are orchestrated by stromal cells will be discovered. Here, we will discuss how the development of lymph nodes as well as their specific niches is guided by the interaction of immune cells and stromal cells.

Most women with epithelial ovarian cancer (EOC) suffer from peritoneal carcinomatosis upon first clinical presentation. Extensive peritoneal carcinomatosis has a poor prognosis and its pathophysiology is not well understood. Although treatment with systemic intravenous chemotherapy is often initially successful, peritoneal recurrences occur regularly. We hypothesized that insufficient or poorly-perfused microvasculature may impair the therapeutic efficacy of systemic intravenous chemotherapy but may also limit expansive and invasive growth characteristic of peritoneal EOC metastases. In 23 patients with advanced EOC or suspicion thereof, we determined the angioarchitecture and perfusion of the microvasculature in peritoneum and in peritoneal metastases using incident dark field (IDF) imaging. Additionally, we performed immunohistochemical analysis and 3-dimensional (3D) whole tumor imaging using light sheet fluorescence microscopy of IDF-imaged tissue sites. In all metastases, microvasculature was present but the angioarchitecture was chaotic and the vessel density and perfusion of vessels was significantly lower than in unaffected peritoneum. Immunohistochemical analysis showed expression of vascular endothelial growth factor and hypoxia inducible factor 1α, and 3D imaging demonstrated vascular continuity between metastases and the vascular network of the peritoneum beneath the elastic lamina of the peritoneum. We conclude that perfusion of the microvasculature within metastases is limited, which may cause hypoxia, affect the behavior of EOC metastases on the peritoneum and limit the response of EOC metastases to systemic treatment. Electronic supplementary material The online version of this article (10.1007/s10585-020-10024-4) contains supplementary material, which is available to authorized users.

Specialized stromal cells occupy and help define B- and T cell domains, which is crucial for proper functioning of our immune system. Signaling through lymphotoxin and TNF-receptors is crucial for development of different stromal subsets which are thought to arise from a common precursor. However, mechanisms that control the selective generation of the different stromal phenotypes are not known.Here we show that in mice, retinoic acid mediated signaling is important for the differentiation of precursors towards the Cxcl13pos follicular dendritic cell (FDC) lineage, while blocking lymphotoxin mediated Ccl19pos fibroblastic reticular cell (FRC) lineage differentiation. Consequently, we see at day of birth Cxcl13posCcl19neg/low and Cxcl13neg/lowCcl19pos cells within neonatal lymph nodes.Furthermore, ablation of retinoic acid receptor signaling in stromal precursors early after birth reduces Cxcl13 expression, while in addition, complete blockade of retinoic acid signaling prevents formation of FDC networks in lymph nodes.

Insulin-mediated microvascular recruitment (IMVR) regulates delivery of insulin and glucose to insulin-sensitive tissues. We have previously proposed that perivascular adipose tissue (PVAT) controls vascular function through outside-to-inside communication and through vessel-to-vessel, or "vasocrine" signaling. However, direct experimental evidence supporting a role of local PVAT in regulating IMVR and insulin sensitivity in vivo is lacking. Here, we studied muscles with and without PVAT in mice using combined contrast-enhanced ultrasonography and intravital microscopy to measure IMVR and gracilis artery (GA) diameter at baseline and during the hyperinsulinemic-euglycemic clamp. We show, using microsurgical removal of PVAT from the muscle microcirculation, that local PVAT depots regulate insulin-stimulated muscle perfusion and glucose uptake in vivo We discovered direct microvascular connections between PVAT and the distal muscle microcirculation, or adipomuscular arterioles, removal of which abolished IMVR. Local removal of intramuscular PVAT altered protein clusters in the connected muscle, including upregulation of a cluster featuring heat shock proteins 90ab1 and 70 and downregulation of a cluster of mitochondrial protein components of complexes III, IV and V. These data highlight the importance of PVAT in vascular and metabolic physiology, and are likely relevant for obesity and diabetes.

Innate lymphoid cells (ILCs) guard epithelial tissue integrity during homeostasis, but can be potent immune effector cells during inflammation. Precursors to all ILC subsets (ILC precursors [ILCP]) have been identified in human peripheral blood (PB). We found that during homeostasis, ILCP in PB of mouse and human expressed homing receptors for secondary lymphoid organs, mainly CD62L. These ILCP entered mouse lymph nodes in a CD62L-dependent way and relied on S1P receptors for their exit. Importantly, CD62L expression was absent on human ILCs expressing NKp44 in tonsils and PB of Crohn disease patients, and relatively fewer CD62L+ ILCP were present in PB of Crohn disease patients. These data are in agreement with selective expression of CD62L on nonactivated ILCP. As such, we conclude that CD62L not only serves as a functional marker of ILCP, but has potential to be used in the clinic as a diagnostic marker in inflammatory disorders.

Blood vascular endothelial cells (BECs) control the immune response by regulating immune cell recruitment, metabolite exchange and blood flow in lymphoid tissues. However, the diversity of BEC and their origins during immune angiogenesis remain poorly understood. Here we profile transcriptomes of BEC from mouse peripheral lymph nodes and map key phenotypes to the vasculature. Our analysis identifies multiple novel subsets including a venous population whose gene signature predicts an unexpectedly selective role in myeloid cell (vs lymphocyte) recruitment to the medulla, confirmed by 2 photon videomicroscopy. We define five phenotypes of capillary lining BEC including a capillary resident regenerative population (CRP) that displays stem cell and migratory gene signatures and contributes to homeostatic BEC turnover and to vascular neogenesis after immunization. Trajectory analyses reveal retention of developmental programs along a progression of cellular phenotypes from CRP to mature venous and arterial BEC subsets. Overall, our single cell atlas provides a molecular blueprint of the lymph node blood vasculature and defines subset specialization for immune cell recruitment and vascular homeostasis.

Summary The tissue dynamics that govern maintenance and regeneration of the pancreas remain largely unknown. In particular, the presence and nature of a cellular hierarchy remains a topic of debate. Previous lineage tracing strategies in the pancreas relied on specific marker genes for clonal labeling, which left other populations untested and failed to account for potential widespread phenotypical plasticity. Here we employed a tracing system that depends on replication-induced clonal marks. We found that, in homeostasis, steady acinar replacement events characterize tissue dynamics, to which all acinar cells have an equal ability to contribute. Similarly, regeneration following pancreatitis was best characterized by an acinar self-replication model because no evidence of a cellular hierarchy was detected. In particular, rapid regeneration in the pancreas was found to be driven by an accelerated rate of acinar fission-like events. These results provide a comprehensive and quantitative model of cell dynamics in the exocrine pancreas., Graphical abstract, Highlights • All acinar cells have an equal probability to contribute to tissue renewal • All acinar cells function as bona fide progenitor cells during homeostasis • Acinar fission-like events underlie pancreas regeneration, The dynamics of tissue maintenance in the adult exocrine pancreas are largely unknown. In this study, Lodestijn et al. use a combination of experimental and computational methods to reveal that there is no hierarchy in the adult exocrine pancreas and that all cells can act as bona fide progenitors.

The tissue dynamics that govern maintenance and regeneration of the pancreas remain largely unknown. In particular, the presence and nature of a cellular hierarchy remains a topic of debate. Previous lineage tracing strategies in the pancreas relied on specific marker genes for clonal labeling, which leaves other populations untested and fails to account for potential widespread phenotypical plasticity. Here we employed a tracing system that depends on replication-induced clonal marks. We found that in homeostasis, steady acinar replacement events characterize tissue dynamics, to which all acinar cells have an equal ability to contribute. Similarly, regeneration following pancreatitis was best characterized by an acinar self-replication model, as no evidence for a cellular hierarchy was detected. In particular, rapid regeneration in the pancreas was found to be driven by an accelerated rate of acinar fission events. Together these results provide a comprehensive and quantitative model of cell dynamics in the exocrine pancreas.

Factors regulating leukocyte migration to neonatal lymph nodes are not sufficiently identified. In this issue of Immunity, Zhang et al. (2016) reveal that fungi drive emigration of gut DCs to lymph nodes, where these DCs instruct endothelial cell receptivity to leukocytes.

During embryogenesis, lymph nodes form through intimate interaction between lymphoid tissue inducer and lymphoid tissue organizer (LTo) cells. Shortly after birth in mice, specialized stromal cell subsets arise that organize microenvironments within the lymph nodes; however, their direct precursors have not yet been identified. In the bone marrow, mesenchymal stem cells are labeled with GFP in nestin-GFP mice, and we show that during all stages of development, nestin+ cells are present within lymph nodes of these mice. At day of birth, both mesenchymal CD31− and endothelial CD31+ LTo cells were GFP+, and only the population of CD31− LTo cells contained mesenchymal precursors. These CD31−nestin+ cells are found in the T and B cell zones or in close association with high endothelial venules in adult lymph nodes. Fate mapping of nestin+ cells unambiguously revealed the contribution of nestin+ precursor cells to the mesenchymal as well as the endothelial stromal populations within lymph nodes. However, postnatal tamoxifen induced targeting of nestin+ cells in nes-creER mice showed that most endothelial cells and only a minority of the nonendothelial cells were labeled. Overall our data show that nestin+ cells contribute to all subsets of the complex stromal populations that can be found in lymph nodes.

Changes in diet and microbiota have determining effects on the function of the mucosal immune system. For example, the active metabolite of vitamin A, retinoic acid (RA), has been described to maintain homeostasis in the intestine by its influence on both lymphocytes and myeloid cells. Additionally, innate lymphoid cells (ILCs), important producers of cytokines necessary for intestinal homeostasis, are also influenced by vitamin A in the small intestines. In this study, we show a reduction of both NCR− and NCR+ ILC3 subsets in the small intestine of mice raised on a vitamin A–deficient diet. Additionally, the percentages of IL-22–producing ILCs were reduced in the absence of dietary vitamin A. Conversely, mice receiving additional RA had a specific increase in the NCR− ILC3 subset, which contains the lymphoid tissue inducer cells. The dependence of lymphoid tissue inducer cells on vitamin A was furthermore illustrated by impaired development of enteric lymphoid tissues in vitamin A–deficient mice. These effects were a direct consequence of ILC-intrinsic RA signaling, because retinoic acid–related orphan receptor γt–Cre × RARα-DN mice had reduced numbers of NCR− and NCR+ ILC3 subsets within the small intestine. However, lymphoid tissue inducer cells were not affected in these mice nor was the formation of enteric lymphoid tissue, demonstrating that the onset of RA signaling might take place before retinoic acid–related orphan receptor γt is expressed on lymphoid tissue inducer cells. Taken together, our data show an important role for vitamin A in controlling innate lymphoid cells and, consequently, postnatal formed lymphoid tissues within the small intestines.

Introduction The inverse correlation between prevalence of auto-immune disorders like the chronic neuro-inflammatory disease multiple sclerosis (MS) and the occurrence of helminth (worm) infections, suggests that the helminth-trained immune system is protective against auto-immunity. As monocytes are regarded as crucial players in the pathogenesis of auto-immune diseases, we explored the hypothesis that these innate effector cells are prime targets for helminths to exert their immunomodulatory effects. Results Here we show that soluble products of the porcine nematode Trichuris suis (TsSP) are potent in changing the phenotype and function of human monocytes by skewing classical monocytes into anti-inflammatory patrolling cells, which exhibit reduced trans-endothelial migration capacity in an in vitro model of the blood–brain barrier. Mechanistically, we identified the mannose receptor as the TsSP-interacting monocyte receptor and we revealed that specific downstream signalling occurs via protein kinase C (PKC), and in particular PKCδ. Conclusion This study provides comprehensive mechanistic insight into helminth-induced immunomodulation, which can be therapeutically exploited to combat various auto-immune disorders. Electronic supplementary material The online version of this article (doi:10.1186/s40478-015-0223-1) contains supplementary material, which is available to authorized users.

Immunological memory provides long-term protection against reinfection or reactivation of pathogens. Murine memory T cell populations may be compressed following infections with new pathogens. Humans have to retain memory T cells directed against a variety of microbes for many decades. Under these circumstances, the effect of pathogens that mount robust T cell reactivity on the pre-existing memory directed against unrelated microbes is unknown. In this study, we studied peripheral blood memory CD8+ T cells directed against different viruses following primary CMV infection in renal transplant recipients. The entrance of CMV-specific CD8+ T cells expanded the Ag-primed CD8+ T cell compartment rather than competing for space with pre-existing memory T cells specific for persistent or cleared viruses. Neither numbers nor phenotype of EBV- or influenza-specific CD8+ T cells was altered by primary CMV infection. CMV-specific CD8+ T cells accumulated over time, resulting in increased total CD8+ T cell numbers. Additionally, they acquired a highly differentiated cytolytic phenotype that was clearly distinct from EBV- or influenza-reactive T cells. Thus, the human immune system appears to be flexible and is able to expand when encountering CMV. In view of the phenotypic differences between virus-specific T cells, this expansion may take place in cellular niches different from those occupied by EBV- or influenza-specific T cells, thereby preserving immunity to these pathogens.

Non-hematopoietic lymph node stromal cells shape immunity by inducing MHC-I-dependent deletion of self-reactive CD8+ T cells and MHC-II-dependent anergy of CD4+ T cells. In this study, we show that MHC-II expression on lymph node stromal cells is additionally required for homeostatic maintenance of regulatory T cells (Tregs) and maintenance of immune quiescence. In the absence of MHC-II expression in lymph node transplants, i.e. on lymph node stromal cells, CD4+ as well as CD8+ T cells became activated, ultimately resulting in transplant rejection. MHC-II self-antigen presentation by lymph node stromal cells allowed the non-proliferative maintenance of antigen-specific Tregs and constrained antigen-specific immunity. Altogether, our results reveal a novel mechanism by which lymph node stromal cells regulate peripheral immunity. DOI: http://dx.doi.org/10.7554/eLife.04433.001, eLife digest In vertebrates, the immune response that protects against infection and disease is made up of two systems. The body's first line of defense is the innate immune system that attacks invaders rapidly but indiscriminately. If this fails to stop disease progression, the adaptive immune system is activated. Although the adaptive immune response is relatively slow compared with the innate immune response, it is more deliberate and produces cells that specifically target and destroy the pathogen or diseased cells present. The adaptive immune system also produces cells that ‘remember’ the pathogen so that it can be destroyed more quickly if it invades again. A special type of white blood cell, called a T cell, is key to the adaptive immune response. To activate T cells, fragments of molecules that provoke an immune response—called antigens—must be bound to a ‘major histocompatibility complex’ (MHC) and presented to these cells. This process often occurs in lymph nodes, organs that filter the fluid moving from the body's tissues back into the blood. Particular cells in the lymph node, called lymph node stromal cells, are essential for the organ's structure; recently, these cells have also been found to play roles in regulating the immune response. For example, lymph node stromal cells can help to destroy self-reactive T cells that attack the host's normal, healthy cells. In addition, some types of lymph node stromal cells produce major histocompatibility complexes, although exactly what these complexes do on these cells was unknown. Baptista, Roozendaal et al. investigated the role of the major histocompatibility complexes expressed by lymph node stromal cells by transplanting mutant cells that could not produce these complexes into otherwise normal mice. In these mice, T cells became more activated than normal and the transplant was rejected after several weeks. On further investigation, Baptista, Roozendaal et al. discovered that the major histocompatibility complexes produced by the lymph node stromal cells help to maintain an active population of regulatory T cells. These cells are responsible for shutting down the immune response. This work therefore improves our understanding of how the immune response is regulated and could help to develop new strategies for preventing donor organs being rejected after transplantation. DOI: http://dx.doi.org/10.7554/eLife.04433.002

Mesenchymal stem cells (MSCs) show great therapeutic potential for the treatment of various immune mediated diseases, including Multiple Sclerosis (MS). Systemic administration of MSCs during experimental allergic encephalomyelitis (EAE), an animal model for MS, was shown to reduce the infiltration of T cells, B cells, and macrophages into the CNS. Whether endogenous MSCs are mobilized and potentially modulate the severity of disease is not known. Here we show that during the acute phase of EAE, MSCs numbers in the bone marrow were severely reduced, which restored to control levels during the progressive phase of the disease. The number of bone marrow MSCs inversely correlated with the number of both CD4 and CD8 T cells present in the bone marrow indicating a link between activated T cells and MSC mobilization. Analysis of CD70-transgenic mice, which have a constitutively activated immune system and elevated number of activated T cells in the bone marrow, showed severely reduced number of bone marrow MSCs. Transfer of T cells that were activated through their CD27 receptor reduced the number of bone marrow MSCs dependent on IFN-y. These data provide a mechanism by which MSCs can be mobilized from the bone marrow in order to contribute to tissue repair at a distant location.

Aims In patients with obstructive coronary artery disease (CAD), the growth of collateral arteries, i.e. arteriogenesis, can preserve myocardial tissue perfusion and function. Monocytes modulate this process, supplying locally the necessary growth factors and degrading enzymes. Knowledge on factors involved in human arteriogenesis is scarce. Thus, the aim of the present study is to identify targets in monocytes that are critical for arteriogenesis in patients with CAD. Methods and results A total of 50 patients with a chronic total coronary occlusion were dichotomized according to their collateral flow index. From each patient, RNA was isolated from unstimulated peripheral blood monocytes, monocytes stimulated by lipopolysaccharide (LPS) or interleukin (IL)-4, and from macrophages. Increased mRNA expression of galectin-2 was found in three out of four monocytic cell types of patients with a low capacity of the collateral circulation ( P = 0.03 for unstimulated monocytes; P = 0.02 for LPS-stimulated monocytes; P = 0.20 for IL-4-stimulated monocytes; P = 0.02 for macrophages). Additionally, galectin-2 mRNA expression was significantly associated with the rs7291467 polymorphism in LGALS2 encoding galectin-2 in all four monocytic cell types. Patient with the rs7291467 CC genotype displayed highest galectin-2 expression, and also tended to have a lower arteriogenic response. To evaluate the effect of galectin-2 on arteriogenesis in vivo , we used a murine hindlimb model. Treatment with galectin-2 markedly impaired the perfusion restoration at Day 7. Conclusion Collectively, these results identify galectin-2 as a novel inhibitor of arteriogenesis. Modulation of galectin-2 may constitute a new therapeutic strategy for the stimulation of arteriogenesis in patients with CAD.

Lymph nodes are strategically located throughout the body to allow lymphocytes to efficiently encounter their cognate antigen and become activated. The structure of the lymph nodes is such that B and T lymphocytes each have their own microdomain. This structure is provided by lymph node stromal cells, which also provide the lymphocytes with a scaffold upon which to migrate. Here, we discuss how stromal cells differentiate from mesenchymal precursor cells in response to the interaction with lymphocytes, while these stromal cells in turn provide necessary survival factors for the lymphocytes. We propose that during immune reactions, the interactions of stromal and immune cells are similarly important for controlling the expanding lymphocyte pool.

BACKGROUND: Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system in which autoreactive myelin-specific T cells cause extensive tissue damage, resulting in neurological deficits. In the disease process, T cells are primed in the periphery by antigen presenting dendritic cells (DCs). DCs are considered to be crucial regulators of specific immune responses and molecules or proteins that regulate DC function are therefore under extensive investigation. We here investigated the potential immunomodulatory capacity of the ATP binding cassette transporter P-glycoprotein (P-gp). P-gp generally drives cellular efflux of a variety of compounds and is thought to be involved in excretion of inflammatory agents from immune cells, like DCs. So far, the immunomodulatory role of these ABC transporters is unknown. METHODS AND FINDINGS: Here we demonstrate that P-gp acts as a key modulator of adaptive immunity during an in vivo model for neuroinflammation. The function of the DC is severely impaired in P-gp knockout mice (Mdr1a/1b-/-), since both DC maturation and T cell stimulatory capacity is significantly decreased. Consequently, Mdr1a/1b -/- mice develop decreased clinical signs of experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. Reduced clinical signs coincided with impaired T cell responses and T cell-specific brain inflammation. We here describe the underlying molecular mechanism and demonstrate that P-gp is crucial for the secretion of pro-inflammatory cytokines such as TNF-alpha and IFN-gamma. Importantly, the defect in DC function can be restored by exogenous addition of these cytokines. CONCLUSIONS: Our data demonstrate that P-gp downmodulates DC function through the regulation of pro-inflammatory cytokine secretion, resulting in an impaired immune response. Taken together, our work highlights a new physiological role for P-gp as an immunomodulatory molecule and reveals a possible new target for immunotherapy

Biobreeding (BB) rats model type 1 autoimmune diabetes (T1D). BB diabetes-prone (BBDP) rats develop T1D spontaneously. BB diabetes-resistant (BBDR) rats develop T1D after immunological perturbations that include regulatory T cell (Treg) depletion plus administration of low doses of a TLR ligand, polyinosinic-polycytidylic acid. Using both models, we analyzed CD4+CD25+ and CD4+CD45RC− candidate rat Treg populations. In BBDR and control Wistar Furth rats, CD25+ T cells comprised 5–8% of CD4+ T cells. In vitro, rat CD4+CD25+ T cells were hyporesponsive and suppressed T cell proliferation in the absence of TGF-β and IL-10, suggesting that they are natural Tregs. In contrast, CD4+CD45RC− T cells proliferated in vitro in response to mitogen and were not suppressive. Adoptive transfer of purified CD4+CD25+ BBDR T cells to prediabetic BBDP rats prevented diabetes in 80% of recipients. Surprisingly, CD4+CD45RC−CD25− T cells were equally protective. Quantitative studies in an adoptive cotransfer model confirmed the protective capability of both cell populations, but the latter was less potent on a per cell basis. The disease-suppressing CD4+CD45RC−CD25− population expressed PD-1 but not Foxp3, which was confined to CD4+CD25+ cells. We conclude that CD4+CD25+ cells in the BBDR rat act in vitro and in vivo as natural Tregs. In addition, another population that is CD4+CD45RC−CD25− also participates in the regulation of autoimmune diabetes.