Lymphotoxin-alpha contributes to lymphangiogenesis

The roles of tertiary lymphoid structures in genitourinary cancers: molecular mechanisms, therapeutic strategies, and clinical applications

The presence of tertiary lymphoid structures (TLSs) associated with distinct treatment efficacy and clinical prognosis has been identified in various cancer types. However, the mechanistic roles and clinical implications of TLSs in genitourinary (GU) cancers remain incompletely explored. Despite their potential role as predictive markers described in numerous studies, it is essential to comprehensively evaluate the characteristics of TLSs, including drivers of formation, structural foundation, cellular compositions, maturation stages, molecular features, and specific functionality to maximize their positive impacts on tumor-specific immunity. The unique contributions of these structures to cancer progression and biology have fueled interest in these structures as mediators of antitumor immunity. Emerging data are trying to explore the effects of therapeutic interventions targeting TLSs. Therefore, a better understanding of the molecular and phenotypic heterogeneity of TLSs may facilitate the development of TLSs-targeting therapeutic strategies to obtain optimal clinical benefits for GU cancers in the setting of immunotherapy. In this review, the authors focus on the phenotypic and functional heterogeneity of TLSs in cancer progression, current therapeutic interventions targeting TLSs and the clinical implications and therapeutic potential of TLSs in GU cancers.

Lymphatic vessels in the age of cancer immunotherapy

Lymphatic transport maintains homeostatic health and is necessary for immune surveillance, and yet lymphatic growth is often associated with solid tumour development and dissemination. Although tumour-associated lymphatic remodelling and growth were initially presumed to simply expand a passive route for regional metastasis, emerging research puts lymphatic vessels and their active transport at the interface of metastasis, tumour-associated inflammation and systemic immune surveillance. Here, we discuss active mechanisms through which lymphatic vessels shape their transport function to influence peripheral tissue immunity and the current understanding of how tumour-associated lymphatic vessels may both augment and disrupt antitumour immune surveillance. We end by looking forward to emerging areas of interest in the field of cancer immunotherapy in which lymphatic vessels and their transport function are likely key players: the formation of tertiary lymphoid structures, immune surveillance in the central nervous system, the microbiome, obesity and ageing. The lessons learnt support a working framework that defines the lymphatic system as a key determinant of both local and systemic inflammatory networks and thereby a crucial player in the response to cancer immunotherapy.

Repositioning the Early Pathology of Type 1 Diabetes to the Extraislet Vasculature

Type 1 diabetes (T1D) is a prototypic T cell-mediated autoimmune disease. Because the islets of Langerhans are insulated from blood vessels by a double basement membrane and lack detectable lymphatic drainage, interactions between endocrine and circulating T cells are not permitted. Thus, we hypothesized that initiation and progression of anti-islet immunity required islet neolymphangiogenesis to allow T cell access to the islet. Combining microscopy and single cell approaches, the timing of this phenomenon in mice was situated between 5 and 8 wk of age when activated anti-insulin CD4 T cells became detectable in peripheral blood while peri-islet pathology developed. This "peri-insulitis," dominated by CD4 T cells, respected the islet basement membrane and was limited on the outside by lymphatic endothelial cells that gave it the attributes of a tertiary lymphoid structure. As in most tissues, lymphangiogenesis seemed to be secondary to local segmental endothelial inflammation at the collecting postcapillary venule. In addition to classic markers of inflammation such as CD29, V-CAM, and NOS, MHC class II molecules were expressed by nonhematopoietic cells in the same location both in mouse and human islets. This CD45- MHC class II+ cell population was capable of spontaneously presenting islet Ags to CD4 T cells. Altogether, these observations favor an alternative model for the initiation of T1D, outside of the islet, in which a vascular-associated cell appears to be an important MHC class II-expressing and -presenting cell.

Lymphatic malformations: mechanistic insights and evolving therapeutic frontiers

The lymphatic vascular system is gaining recognition for its multifaceted role and broad pathological significance. Once perceived as a mere conduit for interstitial fluid and immune cell transport, recent research has unveiled its active involvement in critical physiological processes and common diseases, including inflammation, autoimmune diseases, and atherosclerosis. Consequently, abnormal development or functionality of lymphatic vessels can result in serious health complications. Here, we discuss lymphatic malformations (LMs), which are localized lesions that manifest as fluid-filled cysts or extensive infiltrative lymphatic vessel overgrowth, often associated with debilitating, even life-threatening, consequences. Genetic causes of LMs have been uncovered, and several promising drug-based therapies are currently under investigation and will be discussed.

Epigenetic targets to enhance antitumor immune response through the induction of tertiary lymphoid structures

Tertiary lymphoid structures (TLS) are ectopic lymphoid aggregates found in sites of chronic inflammation such as tumors and autoimmune diseases. The discovery that TLS formation at tumor sites correlated with good patient prognosis has triggered extensive research into various techniques to induce their formation at the tumor microenvironment (TME). One strategy is the exogenous induction of specific cytokines and chemokine expression in murine models. However, applying such systemic chemokine expression can result in significant toxicity and damage to healthy tissues. Also, the TLS formed from exogenous chemokine induction is heterogeneous and different from the ones associated with favorable prognosis. Therefore, there is a need to optimize additional approaches like immune cell engineering with lentiviral transduction to improve the TLS formation in vivo. Similarly, the genetic and epigenetic regulation of the different phases of TLS neogenesis are still unknown. Understanding these molecular regulations could help identify novel targets to induce tissue-specific TLS in the TME. This review offers a unique insight into the molecular checkpoints of the different stages and mechanisms involved in TLS formation. This review also highlights potential epigenetic targets to induce TLS neogenesis. The review further explores epigenetic therapies (epi-therapy) and ongoing clinical trials using epi-therapy in cancers. In addition, it builds upon the current knowledge of tools to generate TLS and TLS phenotyping biomarkers with predictive and prognostic clinical potential.

Evaluation of lymphotoxin-alpha in pterygium and diagnostic value in active and inactive pterygium states

To explore the correlation between tear LT-a, pterygium status, and dry eye indicators. We established a diagnostic model to evaluate active pterygium. A retrospective study was conducted between June 2021 and June 2023 on 172 patients, comprising 108 men and 64 women. The study analyzed LT-a and various ocular parameters in all participants. The data was collected using Excel software and analyzed using SPSS 25.0 statistical software and Medcalc. We made a nomogram diagnostic model to different diagnosed the state of pterygium. This study found that pterygium has progressive eye surface damage during the active state. There was no significant difference in dry eye indicators between the two groups. However, the concentration of LT-a in the active group was significantly lower than that in the inactive group (P < 0.001). We observed that increased pterygium grade corresponded to a worse ocular surface condition. In addition, LT-a was significantly positively correlated with disease duration, but negatively correlated with age, pterygium size, active pterygium state, and LLT value. The optimal intercept value for evaluating active pterygium in Lt-a was ≤ 0.49 dg/ml. We screened three variables for evaluating active pterygium through Single and Multiple regression analysis: LT-a grading, pterygium size, and congestion score. Finally, we made a reliable diagnostic nomogram model. Pterygium development triggers immune inflammation. Our model based on LT-a identifies active pterygium for personalized treatment options and new research directions.

Tailoring biomaterials for monitoring and evoking tertiary lymphoid structures

Despite the remarkable clinical success of immune checkpoint blockade (ICB) in the treatment of cancer, the response rate to ICB therapy remains suboptimal. Recent studies have strongly demonstrated that intratumoral tertiary lymphoid structures (TLSs) are associated with a good prognosis and a successful clinical response to immunotherapy. However, there is still a shortage of efficient and wieldy approaches to image and induce intratumoral TLSs in vivo. Biomaterials have made great strides in overcoming the deficiencies of conventional diagnosis and therapies for cancer, and antitumor therapy has also benefited from biomaterial-based drug delivery models. In this review, we summarize the reported methods for TLS imaging and induction based on biomaterials and provide potential strategies that can further enhance the effectiveness of imaging and stimulating intratumoral TLSs to predict and promote the response rates of ICB therapies for patients. STATEMENT OF SIGNIFICANCE: In this review, we focused on the promising of biomaterials for imaging and induction of TLSs. We reviewed the applications of biomaterials in molecular imaging and immunotherapy, identified the biomaterials that may be suitable for TLS imaging and induction, and provided outlooks for further research. Accurate imaging and effective induction of TLSs are of great significance for understanding the mechanism and clinical application. We highlighted the need for multidisciplinary coordination and cooperation in this field, and proposed the possible future direction of noninvasive imaging and artificial induction of TLSs based on biomaterials. We believe that it can facilitate collaboration and galvanize a broader effort.

Tenascin-C in Tissue Repair after Myocardial Infarction in Humans

Adverse ventricular remodeling after myocardial infarction (MI) is progressive ventricular dilatation associated with heart failure for weeks or months and is currently regarded as the most critical sequela of MI. It is explained by inadequate tissue repair due to dysregulated inflammation during the acute stage; however, its pathophysiology remains unclear. Tenascin-C (TNC), an original member of the matricellular protein family, is highly up-regulated in the acute stage after MI, and a high peak in its serum level predicts an increased risk of adverse ventricular remodeling in the chronic stage. Experimental TNC-deficient or -overexpressing mouse models have suggested the diverse functions of TNC, particularly its pro-inflammatory effects on macrophages. The present study investigated the roles of TNC during human myocardial repair. We initially categorized the healing process into four phases: inflammatory, granulation, fibrogenic, and scar phases. We then immunohistochemically examined human autopsy samples at the different stages after MI and performed detailed mapping of TNC in human myocardial repair with a focus on lymphangiogenesis, the role of which has recently been attracting increasing attention as a mechanism to resolve inflammation. The direct effects of TNC on human lymphatic endothelial cells were also assessed by RNA sequencing. The results obtained support the potential roles of TNC in the regulation of macrophages, sprouting angiogenesis, the recruitment of myofibroblasts, and the early formation of collagen fibrils during the inflammatory phase to the early granulation phase of human MI. Lymphangiogenesis was observed after the expression of TNC was down-regulated. In vitro results revealed that TNC modestly down-regulated genes related to nuclear division, cell division, and cell migration in lymphatic endothelial cells, suggesting its inhibitory effects on lymphatic endothelial cells. The present results indicate that TNC induces prolonged over-inflammation by suppressing lymphangiogenesis, which may be one of the mechanisms underlying adverse post-infarct remodeling.

Tertiary lymphoid structures are critical for cancer prognosis and therapeutic response

Tertiary lymphoid structures (TLSs) are ectopic lymphocyte aggregates that form at sites of chronic inflammation, including cancers, in non-lymphoid tissues. Although the formation of TLSs is similar to that of secondary lymphoid organs, the pathogenic factors leading to TLS formation in cancerous tissues and the mechanisms underlying the role of these structures in the intra-tumoral adaptive antitumor immune response are not fully understood. The presence of TLSs may impact patient prognosis and treatment outcomes. This review examines the current understanding of TLSs in cancers, including their composition and formation as well as their potential to predict prognosis and therapeutic efficacy. We also summarize strategies to induce TLS formation for cancer treatment.

Programmed death ligand 1 intracellular interactions with STAT3 and focal adhesion protein Paxillin facilitate lymphatic endothelial cell remodeling

Lymphatic endothelial cells (LECs) comprise lymphatic capillaries and vessels that guide immune cells to lymph nodes (LNs) and form the subcapsular sinus and cortical and medullary lymphatic structures of the LN. During an active immune response, the lymphatics remodel to accommodate the influx of immune cells from the tissue, but factors involved in remodeling are unclear. Here, we determined that a TSS motif within the cytoplasmic domain of programmed death ligand 1 (PD-L1), expressed by LECs in the LN, participates in lymphatic remodeling. Mutation of the TSS motif to AAA does not affect surface expression of PD-L1, but instead causes defects in LN cortical and medullary lymphatic organization following immunostimulant, Poly I:C, administration in vivo. Supporting this observation, in vitro treatment of the LEC cell line, SVEC4-10, with cytokines TNFα and IFNα significantly impeded SVEC4-10 movement in the presence of the TSS-AAA cytoplasmic mutation. The cellular movement defects coincided with reduced F-actin polymerization, consistent with differences previously found in dendritic cells. Here, in addition to loss of actin polymerization, we define STAT3 and Paxillin as important PD-L1 binding partners. STAT3 and Paxillin were previously demonstrated to be important at focal adhesions for cellular motility. We further demonstrate the PD-L1 TSS-AAA motif mutation reduced the amount of pSTAT3 and Paxillin bound to PD-L1 both before and after exposure to TNFα and IFNα. Together, these findings highlight PD-L1 as an important component of a membrane complex that is involved in cellular motility, which leads to defects in lymphatic organization.

Tertiary lymphoid structures as unique constructions associated with the organization, education, and function of tumor-infiltrating immunocytes

Tertiary lymphoid structures (TLSs) are formations at sites with persistent inflammatory stimulation, including tumors. These ectopic lymphoid organs mainly consist of chemo-attracting B cells, T cells, and supporting dendritic cells (DCs). Mature TLSs exhibit functional organization for the optimal development and collaboration of adaptive immune response, delivering an augmented effect on the tumor microenvironment (TME). The description of the positive correlation between TLSs and tumor prognosis is reliable only under a certain condition involving the localization and maturation of TLSs. Emerging evidence suggests that underlying mechanisms of the anti-tumor effect of TLSs pave the way for novel immunotherapies. Several approaches have been developed to take advantage of intratumoral TLSs, either by combining it with therapeutic agents or by inducing the neogenesis of TLSs.

Tertiary lymphoid structures in cancer

Ectopic lymphoid aggregates, termed tertiary lymphoid structures (TLSs), are formed in numerous cancer types, and, with few exceptions, their presence is associated with superior prognosis and response to immunotherapy. In spite of their presumed importance, the triggers that lead to TLS formation in cancer tissue and the contribution of these structures to intratumoral immune responses remain incompletely understood. Here, we discuss the present knowledge on TLSs in cancer, focusing on (i) the drivers of TLS formation, (ii) the function and contribution of TLSs to the antitumor immune response, and (iii) the potential of TLSs as therapeutic targets in human cancers.

Interplay of immune and kidney resident cells in the formation of tertiary lymphoid structures in lupus nephritis

Kidney involvement confers significant morbidity and mortality in patients with systemic lupus erythematosus (SLE). The pathogenesis of lupus nephritis (LN) involves diverse mechanisms instigated by elements of the autoimmune response which alter the biology of kidney resident cells. Processes in the glomeruli and in the interstitium may proceed independently albeit crosstalk between the two is inevitable. Podocytes, mesangial cells, tubular epithelial cells, kidney resident macrophages and stromal cells with input from cytokines and autoantibodies present in the circulation alter the expression of enzymes, produce cytokines and chemokines which lead to their injury and damage of the kidney. Several of these molecules can be targeted independently to prevent and reverse kidney failure. Tertiary lymphoid structures with true germinal centers are present in the kidneys of patients with lupus nephritis and have been increasingly recognized to associate with poorer renal outcomes. Stromal cells, tubular epithelial cells, high endothelial vessel and lymphatic venule cells produce chemokines which enable the formation of structures composed of a T-cell-rich zone with mature dendritic cells next to a B-cell follicle with the characteristics of a germinal center surrounded by plasma cells. Following an overview on the interaction of the immune cells with kidney resident cells, we discuss the cellular and molecular events which lead to the formation of tertiary lymphoid structures in the interstitium of the kidneys of mice and patients with lupus nephritis. In parallel, molecules and processes that can be targeted therapeutically are presented.

Staphylococcus aureus-Specific Tissue-Resident Memory CD4+ T Cells Are Abundant in Healthy Human Skin

The skin is an immunocompetent tissue that harbors several kinds of immune cells and a plethora of commensal microbes constituting the skin microbiome. Staphylococcus aureus is a prominent skin pathogen that colonizes a large proportion of the human population. We currently have an incomplete understanding of the correlates of protection against S. aureus infection, however genetic and experimental evidence has shown that CD4⁺ T cells play a key role in orchestrating a protective anti-S. aureus immune response. A high S. aureus-specific memory CD4⁺ T cell response has been reported in the blood of healthy subjects. Since T cells are more abundant in the skin than in blood, we hypothesized that S. aureus-specific CD4⁺ T cells could be present in the skin of healthy individuals. Indeed, we observed proliferation of tissue-resident memory CD4⁺ T cells and production of IL-17A, IL-22, IFN-γ and TNF-β by cells isolated from abdominal skin explants in response to heat-killed S. aureus. Remarkably, these cytokines were produced also during an ex vivo epicutaneous S. aureus infection of human skin explants. These findings highlight the importance of tissue-resident memory CD4⁺ T cells present at barrier sites such as the skin, a primary entry site for S. aureus. Further phenotypical and functional characterization of these cells will ultimately aid in the development of novel vaccine strategies against this elusive pathogen.

Traditional Chinese Medicine Regulating Lymphangiogenesis: A Literature Review

Lymphatic vessels, as an important part of the lymphatic system, form a fine vascular system in humans and play an important role in regulating fluid homeostasis, assisting immune surveillance and transporting dietary lipids. Dysfunction of lymphatic vessels can cause many diseases, including cancer, cardiovascular diseases, lymphedema, inflammation, rheumatoid arthritis. Research on lymphangiogenesis has become increasingly important over the last few decades. Nevertheless, the explicit role of regulating lymphangiogenesis in preventing and treating diseases remains unclear owing to the lack of a deeper understanding of the cellular and molecular pathways of the specific and tissue-specific changes in lymphangiopathy. TCM, consisting of compound extracted from TCM, Injections of single TCM and formula, is an important complementary strategy for treating disease in China. Lots of valuable traditional Chinese medicines are used as substitutes or supplements in western countries. As one of the main natural resources, these TCM are widely used in new drug research and development in Asia. Moreover, as a historical and cultural heritage, TCM has been widely applied to clinical research on lymphangiogenesis leveraging new technologies recently. Available studies show that TCM has an explicit effect on the regulation of lymphatic regeneration. This review aims to clarify the function and mechanisms, especially the inhibitory effect of TCM in facilitating and inhibiting lymphatic regeneration.

Molecular Drivers of Lymphocyte Organization in Vertebrate Mucosal Surfaces: Revisiting the TNF Superfamily Hypothesis

The adaptive immune system of all jawed vertebrates relies on the presence of B and T cell lymphocytes that aggregate in specific body sites to form primary and secondary lymphoid structures. Secondary lymphoid organs include organized MALT (O-MALT) such as the tonsils and Peyer patches. O-MALT became progressively organized during vertebrate evolution, and the TNF superfamily of genes has been identified as essential for the formation and maintenance of O-MALT and other secondary and tertiary lymphoid structures in mammals. Yet, the molecular drivers of O-MALT structures found in ectotherms and birds remain essentially unknown. In this study, we provide evidence that TNFSFs, such as lymphotoxins, are likely not a universal mechanism to maintain O-MALT structures in adulthood of teleost fish, sarcopterygian fish, or birds. Although a role for TNFSF2 (TNF-α) cannot be ruled out, transcriptomics suggest that maintenance of O-MALT in nonmammalian vertebrates relies on expression of diverse genes with shared biological functions in neuronal signaling. Importantly, we identify that expression of many genes with olfactory function is a unique feature of mammalian Peyer patches but not the O-MALT of birds or ectotherms. These results provide a new view of O-MALT evolution in vertebrates and indicate that different genes with shared biological functions may have driven the formation of these lymphoid structures by a process of convergent evolution.

Beyond a Passive Conduit: Implications of Lymphatic Biology for Kidney Diseases

The kidney contains a network of lymphatic vessels that clear fluid, small molecules, and cells from the renal interstitium. Through modulating immune responses and via crosstalk with surrounding renal cells, lymphatic vessels have been implicated in the progression and maintenance of kidney disease. In this Review, we provide an overview of the development, structure, and function of lymphatic vessels in the healthy adult kidney. We then highlight the contributions of lymphatic vessels to multiple forms of renal pathology, emphasizing CKD, transplant rejection, and polycystic kidney disease and discuss strategies to target renal lymphatics using genetic and pharmacologic approaches. Overall, we argue the case for lymphatics playing a fundamental role in renal physiology and pathology and treatments modulating these vessels having therapeutic potential across the spectrum of kidney disease.

Chronic Inflammation: A Common Promoter in Tertiary Lymphoid Organ Neogenesis

Tertiary lymphoid organs (TLOs) frequently develop locally in adults in response to non-resolving inflammation. Chronic inflammation leads to the differentiation of stromal fibroblast cells toward lymphoid tissue organizer-like cells, which interact with lymphotoxin α1β2+ immune cells. The interaction initiates lymphoid neogenesis by recruiting immune cells to the site of inflammation and ultimately leads to the formation of TLOs. Mature TLOs harbor a segregated T-cell zone, B-cell follicles with an activated germinal center, follicular dendritic cells, and high endothelial venules, which architecturally resemble those in secondary lymphoid organs. Since CXCL13 and LTα₁β₂ play key roles in TLO neogenesis, they might constitute potential biomarkers of TLO activity. The well-developed TLOs actively regulate local immune responses and influence disease progression, and they are thereby regarded as the powerhouses of local immunity. In this review, we recapitulated the determinants for TLOs development, with great emphasis on the fundamental role of chronic inflammation and tissue-resident stromal cells for TLO neogenesis, hence offering guidance for therapeutic interventions in TLO-associated diseases.

The Role of Endothelial Cells and TNF-Receptor Superfamily Members in Lymphoid Organogenesis and Function During Health and Inflammation

Lymph nodes (LNs) are crucial for the orchestration of immune responses. LN reactions depend on interactions between incoming and local immune cells, and stromal cells. To mediate these cellular interactions an organized vascular network within the LN exists. In general, the LN vasculature can be divided into two components: blood vessels, which include the specialized high endothelial venules that recruit lymphocytes from the bloodstream, and lymphatic vessels. Signaling via TNF receptor (R) superfamily (SF) members has been implicated as crucial for the development and function of LNs and the LN vasculature. In recent years the role of cell-specific signaling of TNFRSF members in different endothelial cell (EC) subsets and their roles in development and maintenance of lymphoid organs has been elucidated. Here, we discuss recent insights into EC-specific TNFRSF member signaling and highlight its importance in different EC subsets in LN organogenesis and function during health, and in lymphocyte activation and tertiary lymphoid structure formation during inflammation.

Current understanding of lymphatic vessels in the central nervous system

Lymphangiogenesis is associated with some pathological conditions such as inflammation, tissue repair, and tumor growth. Recently, a paradigm shift occurred following the discovery of meningeal lymphatic structures in the human central nervous system (CNS); these structures may be a key drainage route for cerebrospinal fluid (CSF) into the peripheral blood and may also contribute to inflammatory reaction and immune surveillance of the CNS. Lymphatic vessels located along the dural sinuses absorb CSF from the adjacent subarachnoid space and brain interstitial fluid via the glymphatic system, which is composed of aquaporin-4 water channels expressed on perivascular astrocytic end-feet membranes. Magnetic resonance imaging (MRI) clearly visualized these lymphatic vessels in the human dura mater. The conception of some neurological disorders, such as multiple sclerosis and Alzheimer's disease, has been changed by this paradigm shift. Meningeal lymphatic vessels could be a promising therapeutic target for the prevention of neurological disorders. However, the involvement of meningeal lymphatic vessels in the pathophysiology has not been fully elucidated and is the subject of future investigations. In this article, to understand the involvement of meningeal lymphatic vessels in neurological disorders, we review the differences between lymphangiogenesis in the CNS and in other tissues during both developmental and adulthood stages, and pathological conditions that may be associated with meningeal lymphatic vessels in the CNS.

Lymphotoxin-α promotes tumor angiogenesis in HNSCC by modulating glycolysis in a PFKFB3-dependent manner

Tumor angiogenesis is critical for tumor progression as the new blood vessels supply nutrients and facilitate metastasis. Previous studies indicate tumor associated lymphocytes, including B cells and T cells, contribute to tumor angiogenesis and tumor progression. The present study aims to identify the function of Lymphotoxin-α (LT-α), which is secreted by the activated lymphocytes, in the tumor angiogenesis of head and neck squamous cell carcinoma (HNSCC). The coculture system between HNSCC cell line Cal27 and primary lymphocytes revealed that tumor cells promoted the LT-α secretion in the cocultured lymphocytes. In vitro data further demonstrated that LT-α promoted the proliferation, migration and tube formation of human umbilical vein endothelial cells (HUVECs) by enhancing the PFKFB3-mediated glycolytic flux. Genetic and pharmacological inhibition of PFKFB3 suppressed the enhanced proliferation and migration of HUVECs. We further identified that LT-α induced PFKFB3 expression was dependent on the TNFR/NF-κB signaling pathway. In addition, we proved that PFKFB3 blockade decreased the density of CD31 positive blood vessels in HNSCC xenografts. Finally, the results from the human HNSCC tissue array revealed that the expression of LT-α in HNSCC samples positively correlated with microvessel density, lymphocytes infiltration and endothelial PFKFB3 expression. In conclusion, infiltrated lymphocyte secreted LT-α enhances the glycolysis of ECs in a PFKFB3-dependent manner through the classical NF-κB pathway and promotes the proliferation and migration of ECs, which may contribute to the aberrant angiogenesis in HNSCCs. Our study suggests that PFKFB3 blockade is a promising therapeutic approach for HNSCCs by targeting tumor angiogenesis.

Role of iBALT in Respiratory Immunity

Pulmonary respiration inevitably exposes the mucosal surface of the lung to potentially noxious stimuli, including pathogens, allergens, and particulates, each of which can trigger pulmonary damage and inflammation. As inflammation resolves, B and T lymphocytes often aggregate around large bronchi to form inducible Bronchus-Associated Lymphoid Tissue (iBALT). iBALT formation can be initiated by a diverse array of molecular pathways that converge on the activation and differentiation of chemokine-expressing stromal cells that serve as the scaffolding for iBALT and facilitate the recruitment, retention, and organization of leukocytes. Like conventional lymphoid organs, iBALT recruits naïve lymphocytes from the blood, exposes them to local antigens, in this case from the airways, and supports their activation and differentiation into effector cells. The activity of iBALT is demonstrably beneficial for the clearance of respiratory pathogens; however, it is less clear whether it dampens or exacerbates inflammatory responses to non-infectious agents. Here, we review the evidence regarding the role of iBALT in pulmonary immunity and propose that the final outcome depends on the context of the disease.

Tertiary Lymphoid Structures: Autoimmunity Goes Local

Tertiary lymphoid structures (TLS) are frequently observed in target organs of autoimmune diseases. TLS present features of secondary lymphoid organs such as segregated T and B cell zones, presence of follicular dendritic cell networks, high endothelial venules and specialized lymphoid fibroblasts and display the mechanisms to support local adaptive immune responses toward locally displayed antigens. TLS detection in the tissue is often associated with poor prognosis of disease, auto-antibody production and malignancy development. This review focuses on the contribution of TLS toward the persistence of the inflammatory drive, the survival of autoreactive lymphocyte clones and post-translational modifications, responsible for the pathogenicity of locally formed autoantibodies, during autoimmune disease development.

Tertiary Lymphoid Structures Among the World of Noncanonical Ectopic Lymphoid Organizations

Tertiary lymphoid structures (TLOs), also known as ectopic lymphoid structures, are associated with chronic infections and inflammatory diseases. Despite their association with pathology, these structures are actually a normal, albeit transient, component of the immune system and facilitate local immune responses that are meant to mitigate inflammation and resolve infection. Many of the mechanisms controlling the formation and function of tertiary lymphoid structures have been identified, in part by experimentally triggering their formation using defined stimuli under controlled conditions. Here, we introduce the experimental and pathological conditions in which tertiary lymphoid tissues are formed, describe the mechanisms linked to their formation, and discuss their functions in the context of both infection and inflammation.

Cellular and Vascular Components of Tertiary Lymphoid Structures

Inflammatory immune cells recruited at the site of chronic inflammation form structures that resemble secondary lymphoid organs (SLO). These are characterized by segregated areas of prevalent T- or B-cell aggregation, differentiation of high endothelial venules, and local activation of resident stromal cells, including lymphatic endothelial cells. B-cell proliferation and affinity maturation toward locally displayed autoantigens have been demonstrated at these sites, known as tertiary lymphoid structures (TLS). TLS formation during chronic inflammation has been associated with local disease persistence and progression, as well as increased systemic manifestations. While bearing a similar histological structure to SLO, the signals that regulate TLS and SLO formation can diverge and a series of pro-inflammatory cytokines have been ascribed as responsible for TLS formation at different anatomical sites. Moreover, for a long time the structural compartment that regulates TLS homeostasis, including survival and recirculation of leucocytes has been neglected. In this chapter, we summarize the novel data available on TLS formation, structural organization, and the functional and anatomical links connecting TLS and SLOs.

High Endothelial Venules and Lymphatic Vessels in Tertiary Lymphoid Organs: Characteristics, Functions, and Regulation

High endothelial venules (HEVs) and lymphatic vessels (LVs) are essential for the function of the immune system, by providing communication between the body and lymph nodes (LNs), specialized sites of antigen presentation and recognition. HEVs bring in naïve and central memory cells and LVs transport antigen, antigen-presenting cells, and lymphocytes in and out of LNs. Tertiary lymphoid organs (TLOs) are accumulations of lymphoid and stromal cells that arise and organize at ectopic sites in response to chronic inflammation in autoimmunity, microbial infection, graft rejection, and cancer. TLOs are distinguished from primary lymphoid organs – the thymus and bone marrow, and secondary lymphoid organs (SLOs) – the LNs, spleen, and Peyer’s patches, in that they arise in response to inflammatory signals, rather than in ontogeny. TLOs usually do not have a capsule but are rather contained within the confines of another organ. Their structure, cellular composition, chemokine expression, and vascular and stromal support resemble SLOs and are the defining aspects of TLOs. T and B cells, antigen-presenting cells, fibroblast reticular cells, and other stromal cells and vascular elements including HEVs and LVs are all typical components of TLOs. A key question is whether the HEVs and LVs play comparable roles and are regulated similarly to those in LNs. Data are presented that support this concept, especially with regard to TLO HEVs. Emerging data suggest that the functions and regulation of TLO LVs are also similar to those in LNs. These observations support the concept that TLOs are not merely cellular accumulations but are functional entities that provide sites to generate effector cells, and that their HEVs and LVs are crucial elements in those activities.

Coordinated lymphangiogenesis is critical in lymph node development and maturation

BACKGROUND

Lymph node (LN) formation requires multiple but coordinated signaling from intrinsic and extrinsic cellular components during embryogenesis. However, the contribution and role of lymphatic vessels (LVs) in LN formation and maturation are poorly defined. Here, using lymphatic-specific reporters, Prox1-GFP mice and Vegfc^+/LacZ mice, we analyzed migration, assembly, and ingrowth of lymphatic endothelial cells (LECs) in LNs during pre- and postnatal development.

RESULTS

Prox1⁺ LECs form string-like connections rather than lymph sac-like structures until E14.5, but the LEC coverage around LN anlagen completes before birth. Compared to wild-type littermates, Vegfc^+/LacZ mice had markedly smaller LNs in neonates and adults, presumably due to the decrease in LTi cell clusters and migrating Prox1⁺ LECs during embryogenesis. In addition, Vegfc-haploinsufficiency or inhibition of VEGFR3 signaling led to an impairment of LN LV ingrowth, resulting in a significant decrease in LN volume. These data indicate that VEGF-C/VEGFR3 signaling plays a substantial role in normal LN formation through proper migration and organization of LECs.

CONCLUSIONS

Taken together, our results provide compelling evidence that the contribution of LVs through VEGF-C/VEGFR3 signaling is critical in LN development and maturation. Developmental Dynamics 245:1189-1197, 2016. © 2016 Wiley Periodicals, Inc.

The Hepatic Lymphatic Vascular System: Structure, Function, Markers, and Lymphangiogenesis

The lymphatic vascular system has been minimally explored in the liver despite its essential functions including maintenance of tissue fluid homeostasis. The discovery of specific markers for lymphatic endothelial cells has advanced the study of lymphatics by methods including imaging, cell isolation, and transgenic animal models and has resulted in rapid progress in lymphatic vascular research during the last decade. These studies have yielded concrete evidence that lymphatic vessel dysfunction plays an important role in the pathogenesis of many diseases. This article reviews the current knowledge of the structure, function, and markers of the hepatic lymphatic vascular system as well as factors associated with hepatic lymphangiogenesis and compares liver lymphatics with those in other tissues.

Malignant T cells express lymphotoxin α and drive endothelial activation in cutaneous T cell lymphoma

Lymphotoxin α (LTα) plays a key role in the formation of lymphatic vasculature and secondary lymphoid structures. Cutaneous T cell lymphoma (CTCL) is the most common primary lymphoma of the skin and in advanced stages, malignant T cells spreads through the lymphatic to regional lymph nodes to internal organs and blood. Yet, little is known about the mechanism of the CTCL dissemination. Here, we show that CTCL cells express LTα in situ and that LTα expression is driven by aberrantly activated JAK3/STAT5 pathway. Importantly, via TNF receptor 2, LTα functions as an autocrine factor by stimulating expression of IL-6 in the malignant cells. LTα and IL-6, together with VEGF promote angiogenesis by inducing endothelial cell sprouting and tube formation. Thus, we propose that LTα plays a role in malignant angiogenesis and disease progression in CTCL and may serve as a therapeutic target in this disease.

Pro-lymphangiogenic properties of IFN-γ-activated human dendritic cells

Dendritic cells (DCs) play a crucial role in the initiation of adaptive immune responses. In addition, through the release of pro- and anti-angiogenic mediators, DCs are key regulators of blood vessel remodeling, a process that characterizes inflammation. Less information is available on the role of DCs in lymphangiogenesis. This study reports that human DCs produce VEGF-C, a cytokine with potent pro-lymphangiogenic activity when stimulated with IFN-γ. DC-derived VEGF-C was biologically active, being able to promote tube-like structure formation in cultures of human lymphatic endothelial cells (LECs). DCs co-cultured with IL-15-activated NK cells produced high levels of VEGF-C, suggesting a role for NK-DC cross-talk in peripheral lymphoid and non-lymphoid tissues in inflammation-associated lymphangiogenesis. Induction of VEGF-C by IFN-γ was detected also in other myeloid cells, such as blood-purified CD1c(+) DCs, CD14(+) monocytes and in monocyte-derived macrophages. In all these cell types, VEGF-C was found associated with the cell membrane by low affinity, heparan sulphate-mediated, interactions. Therefore, human DCs should be considered as new players in inflammation-associated lymphangiogenesis.

Infiltration of M2-polarized macrophages in infected lymphatic malformations: possible role in disease progression

BACKGROUND

Lymphatic malformations (LMs), slow-flow vascular anomalies resulting from abnormal development of lymphatic channels, often progress rapidly after trauma or infection.

OBJECTIVES

To explore the possible mechanism by which local infection promotes the progression of LMs.

METHODS

Immunohistochemistry in serial sections and immunofluorescence were performed to label polarized macrophages. Tertiary lymphoid organs (TLOs) in LMs were identified using antibodies against CD3 (a T-cell marker), CD20 (a B-cell marker) and PNAd (a high endothelial venule marker). Pearson's correlation and cluster analysis were carried out to delineate the relationship between macrophage infiltration and TLO formation. Rat models of LM were established to examine the role of lipopolysaccharide in LM development.

RESULTS

Compared with normal skin tissues, both M1- and M2-polarized macrophages were prevalent in LMs. Moreover, M2-polarized macrophages were significantly increased in infected LMs with an elevated density of TLOs. M2-polarized macrophages were observed in the centre of TLOs accompanied by intensive staining of macrophage colony-stimulating factor, a strong chemotactic factor for monocytes/macrophages, suggesting that macrophages might be recruited through TLOs. Cluster analysis and Pearson's correlation suggested a close relationship between macrophage infiltration and TLO formation. Furthermore, the expression of CD68 was also correlated with that of vascular endothelial growth factor (VEGF)-C and Ki67. Importantly, in an established LM rat model, lipopolysaccharide promoted the progression of the malformations with increased macrophage infiltration and TLO formation.

CONCLUSIONS

M2-polarized macrophages that may be recruited through TLOs in infected LMs may contribute to the progression of the disease by secreting VEGF-C, and therefore accelerating the proliferation of lymphatic endothelial cells.

Lymphangiogenesis and Inflammation-Looking for the "Missing Pieces" of the Puzzle

Several papers about lymphangiogenesis and inflammation focused on the detailed and complicated descriptions of the molecular pathways accompanying both non-tumor and tumor inflammatory-induced lymphatic vessel development. Many authors are tempted to present inflammatory-induced lymphangiogenesis in pathologic conditions neglecting the role of inflammatory cells during embryonic lymphatic vessel development. Some of the inflammatory cells are largely characterized in inflammatory-induced lymphangiogenesis, while others as mast cells, eosinophils, or plasma cells are less studied. No phenotypic characterization of inflammation-activated lymphatic endothelial cell is available in this moment. Another paradox is related to the existence of few papers regarding lymphangiogenesis inside lymphoid organs and for their related pathology. There are still several "missing pieces of such a big puzzle" of lymphangiogenesis and inflammation, with a direct impact on the ineffectiveness of the anti-inflammatory therapy as lymphangiogenesis inhibitors. The present paper will focus on the controversial issues of lymphangiogenesis and inflammation.

Intermittent administration of parathyroid hormone ameliorates periapical lesions in mice

INTRODUCTION

Intermittent administration of parathyroid hormone (PTH) promotes oral osseous wound healing and protects against ligature-induced alveolar bone loss. However, its therapeutic value on periapical periodontitis is unknown. The goal of this study was to determine the effect of intermittent PTH administration on the progression of periapical periodontitis.

METHODS

Seven lymphotoxin alpha-deficient mice received pulp exposures of mandibular first and second molars. Exposed pulp in the right mandible was covered with plaque-contaminated fibrin, whereas exposed pulp in the left mandible was left open. After 4 weeks, the periapical tissues were examined to determine the effect of plaque-contaminated fibrin to induce periapical lesions. Fourteen mice received pulp exposure covered with plaque-contaminated fibrin. PTH (40 μg/kg/d) was administered intermittently to half of the mice for 3 weeks beginning 1 week after pulp exposure. The remaining half received saline injections as the vehicle control. At sacrifice, mandibles and tibiae were harvested and processed for histologic examination. Evaluation of neutrophils and blood vessels was performed after staining with immunofluorescence, and periradicular bone was histomorphometrically analyzed.

RESULTS

The exposed pulp covered with plaque-contaminated fibrin resulted in significantly larger periapical lesions compared with the control. Intermittent PTH administration reduced the size of periapical lesions significantly. Significantly less neutrophil infiltration around the root apex was found in PTH-treated animals compared with the control.

CONCLUSIONS

PTH treatment suppressed periapical inflammation by reducing neutrophil infiltration and protected against tissue destruction by periapical periodontitis.

Lymphotoxin-α keeps the gate open for T-cell infiltration in cHL

In this issue of Blood, Fhu et al report that Reed-Sternberg cell-derived lymphotoxin-α activates endothelial cells to enhance T-cell recruitment in classical Hodgkin lymphoma (cHL), a process that is regulated by cyclooxygenase/nuclear factor-κB/activator protein 1 signaling pathways.

Interplay between Inflammatory Responses and Lymphatic Vessels

Lymphatic vessels are routes for leukocyte migration and fluid drainage. In addition to their passive roles in migration of leukocytes, increasing evidence indicates their active roles in immune regulation. Tissue inflammation rapidly induces lymphatic endothelial cell proliferation and chemokine production, thereby resulting in lymphangiogenesis. Furthermore, lymphatic endothelial cells induce T cell tolerance through various mechanisms. In this review, we focus on the current knowledge on how inflammatory cytokines affect lymphangiogenesis and the roles of lymphatic vessels in modulating immune responses.

Identification of novel genes associated with renal tertiary lymphoid organ formation in aging mice

A hallmark of aging-related organ deterioration is a dysregulated immune response characterized by pathologic leukocyte infiltration of affected tissues. Mechanisms and genes involved are as yet unknown. To identify genes associated with aging-related renal infiltration, we analyzed kidneys from aged mice (≥20 strains) for infiltrating leukocytes followed by Haplotype Association Mapping (HAM) analysis. Immunohistochemistry revealed CD45⁺ cell clusters (predominantly T and B cells) in perivascular areas coinciding with PNAd⁺ high endothelial venules and podoplanin⁺ lymph vessels indicative of tertiary lymphoid organs. Cumulative cluster size increased with age (analyzed at 6, 12 and 20 months). Based on the presence or absence of clusters in male and female mice at 20 months, HAM analysis revealed significant associations with loci on Chr1, Chr2, Chr8 and Chr14 in male mice, and with loci on Chr4, Chr7, Chr13 and Chr14 in female mice. Wisp2 (Chr2) showed the strongest association (P = 5.00×10⁻¹³⁷) in male mice; Ctnnbip1 (P = 6.42×10⁻²⁶⁷) and Tnfrsf8 (P = 5.42×10⁻²⁴⁵) (both on Chr4) showed the strongest association in female mice. Both Wisp2 and Ctnnbip1 are part of the Wnt-signaling pathway and the encoded proteins were expressed within the tertiary lymphoid organs. In conclusion, this study revealed differential lymphocytic infiltration and tertiary lymphoid organ formation in aged mouse kidneys across different inbred mouse strains. HAM analysis identified candidate genes involved in the Wnt-signaling pathway that may be causally linked to tertiary lymphoid organ formation.

Lymphatic vessels and tertiary lymphoid organs

Tertiary lymphoid organs (TLOs) are accumulations of lymphoid cells in chronic inflammation that resemble LNs in their cellular content and organization, high endothelial venules, and lymphatic vessels (LVs). Although acute inflammation can result in defective LVs, TLO LVs appear to function normally in that they drain fluid and transport cells that respond to chemokines and sphingosine-1-phosphate (S1P) gradients. Molecular regulation of TLO LVs differs from lymphangiogenesis in ontogeny with a dependence on cytokines and hematopoietic cells. Ongoing work to elucidate the function and molecular regulation of LVs in TLOs is providing insight into therapies for conditions as diverse as lymphedema, autoimmunity, and cancer.

Inflammation-associated lymphangiogenesis: a double-edged sword?

Lymphangiogenesis and lymphatic vessel remodeling are complex biological processes frequently observed during inflammation. Accumulating evidence indicates that inflammation-associated lymphangiogenesis (IAL) is not merely an endpoint event, but actually a phenomenon actively involved in the pathophysiology of various inflammatory disorders. The VEGF-C/VEGFR-3 and VEGF-A/VEGF-R2 signaling pathways are two of the best-studied pathways in IAL. Methods targeting these molecules, such as prolymphangiogenic or antilymphatic treatments, were found to be beneficial in various preclinical and/or clinical studies. This Review focuses on the most recent achievements in the fields of lymphatic biology relevant to inflammatory conditions. Additionally, preclinical and clinical therapies that modulate IAL are summarized.

Role of the Lymphotoxin/LIGHT System in the Development and Maintenance of Reticular Networks and Vasculature in Lymphoid Tissues

Lymphoid organs are meeting zones where lymphocytes come together and encounter antigens present in the blood and lymph or as delivered by cells migrating from the draining tissue bed. The exquisite efficiency of this process relies heavily on highly specialized anatomy to direct and position the various players. Gated entry and exit control access to these theaters and reticular networks and associated chemokines guide cells into the proper sections. Lymphoid tissues are remarkably plastic, being able to expand dramatically and then involute upon resolution of the danger. All of the reticular scaffolds and vascular and lymphatic components adapt accordingly. As such, the lymph node (LN) is a wonderful example of a physiologic remodeling process and is potentially a guide to study such elements in pathological settings such as fibrosis, chronic infection, and tumor metastasis. The lymphotoxin/LIGHT axis delivers critical differentiation signals that direct and hone differentiation of both reticular networks and the vasculature. Considerable progress has been made recently in understanding the mesenchymal differentiation pathways leading to these specialized networks and in the remodeling that occurs in reactive LNs. In this article, we will review some new advances in the area in terms of developmental, differentiation, and maintenance events mediated by this axis.

Inflammation-induced lymphangiogenesis and lymphatic dysfunction

The lymphatic system is intimately linked to tissue fluid homeostasis and immune cell trafficking. These functions are paramount in the establishment and development of an inflammatory response. In the past decade, an increasing number of reports has revealed that marked changes, such as lymphangiogenesis and lymphatic contractile dysfunction occur in both vascular and nodal parts of the lymphatic system during inflammation, as well as other disease processes. This review provides a critical update on the role of the lymphatic system in disease process such as chronic inflammation and cancer and examines the changes in lymphatic functions the diseases cause and the influence these changes have on the progression of the diseases.

Development of secondary lymphoid organs in relation to lymphatic vasculature

Although the initial event in lymphatic endothelial specification occurs slightly before the initiation of lymph node formation in mice, the development of lymphatic vessels and lymph nodes occurs within the same embryonic time frame. Specification of lymphatic endothelial cells starts around embryonic day 10 (E10), followed by endothelial cell budding and formation of the first lymphatic structures. Through lymphatic endothelial cell sprouting these lymph sacs give rise to the lymphatic vasculature which is complete by E15.5 in mice. It is within this time frame that lymph node formation is initiated and the first structure is secured in place. As lymphatic vessels are crucially involved in the functionality of the lymph nodes, the recent insight that both structures depend on common developmental signals for their initiation provides a molecular mechanism for their coordinated formation. Here, we will describe the common developmental signals needed to properly start the formation of lymphatic vessels and lymph nodes and their interdependence in adult life.

Therapeutic use of dendritic cells to promote the extranodal priming of anti-tumor immunity

Ectopic lymphoid tissue, also known as tertiary lymphoid organs (TLO) develop adaptively within sites of chronic tissue inflammation, thereby allowing the host to efficiently crossprime specific immune effector cells within sites of disease. Recent evidence suggests that the presence of TLO in the tumor microenvironment (TME) predicts better overall survival. We will discuss the relevance of extranodal T cell priming within the TME as a means to effectively promote anti-tumor immunity and the strategic use of dendritic cell (DC)-based therapies to reinforce this clinically preferred process in the cancer-bearing host.

The inflammatory response of lymphatic endothelium

Lymphatic vessels have traditionally been regarded as a rather inert drainage system, which just passively transports fluids, leukocytes and antigen. However, it is becoming increasingly clear that the lymphatic vasculature is highly dynamic and plays a much more active role in inflammatory and immune processes. Tissue inflammation induces a rapid, stimulus-specific upregulation of chemokines and adhesion molecules in lymphatic endothelial cells and a proliferative expansion of the lymphatic network in the inflamed tissue and in draining lymph nodes. Moreover, increasing evidence suggests that inflammation-induced changes in the lymphatic vasculature have a profound impact on the course of inflammatory and immune responses, by modulating fluid drainage, leukocyte migration or the removal of inflammatory mediators from tissues. In this review we will summarize and discuss current knowledge of the inflammatory response of lymphatic endothelium and of inflammation-induced lymphangiogenesis and the current perspective on the overall functional significance of these processes.

Lymphatic vessel function in head and neck inflammation

BACKGROUND

Serious infections of the head and neck cause lymphedema that can lead to airway compromise and oropharyngeal obstruction. Lymphangiogenesis occurs in the head and neck during infection and after immunization. The goal of this project was to develop tools to image lymphatic vessels in living animals and to be able to isolate individual lymphatic endothelial cells in order to quantify changes in single cells caused by inflammation.

METHODS

The ProxTom transgenic red-fluorescent reporter mouse was developed specifically for the purpose of imaging lymphatic vessels in vivo. Prox1 is a transcription factor that is necessary for lymphangiogenesis in development and for the maintenance of lymphatics in adulthood. Mice were immunized and their lymphatic vessels in lymph nodes were imaged in vivo. Individual lymphatic endothelial cells were isolated by means of their fluorescence.

RESULTS

The ProxTom transgene has the red-fluorescent reporter td-Tomato under the control of Prox1 regulatory elements. tdTomato was faithfully expressed in lymphatic vessels coincident with endogenous Prox1 expression. We show lymphangiogenesis in vivo after immunization and demonstrate a method for the isolation of lymphatic endothelial cells by their tdTomato red-fluorescence.

CONCLUSIONS

The faithful expression of the red-fluorescent reporter in the lymphatic vessels of ProxTom means that these mice have proven utility for in vivo study of lymphatic vessels in the immune response. ProxTom has been made available for distribution from the Jackson Laboratory: http://jaxmice.jax.org/strain/018128.html .

PI3K p110δ is expressed by gp38(-)CD31(+) and gp38(+)CD31(+) spleen stromal cells and regulates their CCL19, CCL21, and LTβR mRNA levels

The role of p110δ PI3K in lymphoid cells has been studied extensively, showing its importance in immune cell differentiation, activation and development. Altered T cell localization in p110δ-deficient mouse spleen suggested a role for p110δ in non-hematopoietic stromal cells, which maintain hematopoietic cell segregation. We tested this hypothesis using p110δ^WT/WT mouse bone marrow to reconstitute lethally irradiated p110δ^WT/WT or p110δ^D910A/D910A (which express catalytically inactive p110δ) recipients, and studied localization, number and percentage of hematopoietic cell subsets in spleen and lymph nodes, in homeostatic conditions and after antigen stimulation. These analyses showed diffuse T cell areas in p110δ^D910A/D910A and in reconstituted p110δ^D910A/D910A mice in homeostatic conditions. In these mice, spleen CD4⁺ and CD8⁺ T cell numbers did not increase in response to antigen, suggesting that a p110δ^D910A/D910A stroma defect impedes correct T cell response. FACS analysis of spleen stromal cell populations showed a decrease in the percentage of gp38⁻CD31⁺ cells in p110δ^D910A/D910A mice. qRT-PCR studies detected p110δ mRNA expression in p110δ^WT/WT spleen gp38⁻CD31⁺ and gp38⁺CD31⁺ subsets, which was reduced in p110δ^D910A/D910A spleen. Lack of p110δ activity in these cell populations correlated with lower LTβR, CCL19 and CCL21 mRNA levels; these molecules participate in T cell localization to specific spleen areas. Our results could explain the lower T cell numbers and more diffuse T cell areas found in p110δ^D910A/D910A mouse spleen, as well as the lower T cell expansion after antigen stimulation in p110δ^D910A/D910A compared with p110δ^WT/WT mice.

Interleukin-7 is produced by afferent lymphatic vessels and supports lymphatic drainage

The cytokine interleukin (IL)-7 exerts essential roles in lymph node (LN) organogenesis and lymphocyte development and homeostasis. Recent studies have identified lymphatic endothelial cells (LECs) as a major source of IL-7 in LNs. Here, we report that LECs not only produce IL-7, but also express the IL-7 receptor chains IL-7Rα and CD132. Stimulation with recombinant IL-7 enhanced LEC in vitro activity and induced lymphangiogenesis in the cornea of wild-type (WT) mice. Whereas in IL-7Rα(-/-) mice, dermal lymphatic vessels (LVs) were abnormally organized and lymphatic drainage was compromised, transgenic overexpression of IL-7 in mice resulted in an expanded dermal LV network with increased drainage function. Moreover, systemic treatment with recombinant IL-7 enhanced lymphatic drainage in the skin of WT mice and of mice devoid of lymphocytes. Experiments in IL-7Rα(-/-) bone marrow chimeras demonstrated that the drainage-enhancing activity of IL-7 was exclusively dependent on IL-7Rα expression in stromal but not in hematopoietic cells. Finally, near-infrared in vivo imaging performed in IL-7Rα(-/-) mice revealed that the pumping activity of collecting vessels was normal but fluid uptake into lymphatic capillaries was defective. Overall, our data point toward an unexpected new role for IL-7 as a potential autocrine mediator of lymphatic drainage.