Lymphocyte trafficking across high endothelial venules: dogmas and enigmas

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn’s disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer’s disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

LFA-1 in T cell priming, differentiation, and effector functions

The integrin LFA-1 is crucial for T cell entry into mammalian lymph nodes and tissues, and for promoting interactions with antigen-presenting cells (APCs). However, it is increasingly evident that LFA-1 has additional key roles beyond the mere support of adhesion between T cells, the endothelium, and/or APCs. These include roles in homotypic T cell-T cell (T-T) communication, the induction of intracellular complement activity underlying Th1 effector cell polarization, and the support of long-lasting T cell memory. Here, we briefly summarize current knowledge of LFA-1 biology, discuss novel cytoskeletal regulators of LFA-1 functions, and review new aspects of LFA-1 mechanobiology that are relevant to its function in immunological synapses and in specific pathologies arising from LFA-1 dysregulation.

Stepwise transmigration of T- and B cells through a perivascular channel in high endothelial venules

High endothelial venules (HEVs) effectively recruit circulating lymphocytes from the blood to lymph nodes. HEVs have endothelial cells (ECs) and perivascular sheaths consisting of fibroblastic reticular cells (FRCs). Yet, post-luminal lymphocyte migration steps are not well elucidated. Herein, we performed intravital imaging to investigate post-luminal T- and B-cell migration in popliteal lymph node, consisting of trans-EC migration, crawling in the perivascular channel (a narrow space between ECs and FRCs) and trans-FRC migration. The post-luminal migration of T cells occurred in a PNAd-dependent manner. Remarkably, we found hot spots for the trans-EC and trans-FRC migration of T- and B cells. Interestingly, T- and B cells preferentially shared trans-FRC migration hot spots but not trans-EC migration hot spots. Furthermore, the trans-FRC T-cell migration was confined to fewer sites than trans-EC T-cell migration, and trans-FRC migration of T- and B cells preferentially occurred at FRCs covered by CD11c+ dendritic cells in HEVs. These results suggest that HEV ECs and FRCs with perivascular DCs delicately regulate T- and B-cell entry into peripheral lymph nodes.

High endothelial venules (HEVs) in immunity, inflammation and cancer

High endothelial venules (HEVs) are specialized blood vessels mediating lymphocyte trafficking to lymph nodes (LNs) and other secondary lymphoid organs. By supporting high levels of lymphocyte extravasation from the blood, HEVs play an essential role in lymphocyte recirculation and immune surveillance for foreign invaders (bacterial and viral infections) and alterations in the body’s own cells (neoantigens in cancer). The HEV network expands during inflammation in immune-stimulated LNs and is profoundly remodeled in metastatic and tumor-draining LNs. HEV-like blood vessels expressing high levels of the HEV-specific sulfated MECA-79 antigens are induced in non-lymphoid tissues at sites of chronic inflammation in many human inflammatory and allergic diseases, including rheumatoid arthritis, Crohn’s disease, allergic rhinitis and asthma. Such vessels are believed to contribute to the amplification and maintenance of chronic inflammation. MECA-79⁺ tumor-associated HEVs (TA-HEVs) are frequently found in human tumors in CD3⁺ T cell-rich areas or CD20⁺ B-cell rich tertiary lymphoid structures (TLSs). TA-HEVs have been proposed to play important roles in lymphocyte entry into tumors, a process essential for successful antitumor immunity and lymphocyte-mediated cancer immunotherapy with immune checkpoint inhibitors, vaccines or adoptive T cell therapy. In this review, we highlight the phenotype and function of HEVs in homeostatic, inflamed and tumor-draining lymph nodes, and those of HEV-like blood vessels in chronic inflammatory diseases. Furthermore, we discuss the role and regulation of TA-HEVs in human cancer and mouse tumor models.

Suppression of Rheumatoid Arthritis by Enhanced Lymph Node Trafficking of Engineered Interleukin-10 in Murine Models

OBJECTIVE

Rheumatoid arthritis (RA) is a major autoimmune disease that causes synovitis and joint damage. Although clinical trials have been performed using interleukin-10 (IL-10), an antiinflammatory cytokine, as a potential treatment of RA, the therapeutic effects of IL-10 have been limited, potentially due to insufficient residence in lymphoid organs, where antigen recognition primarily occurs. This study was undertaken to engineer an IL-10-serum albumin (SA) fusion protein and evaluate its effects in 2 murine models of RA.

METHODS

SA-fused IL-10 (SA-IL-10) was recombinantly expressed. Mice with collagen antibody-induced arthritis (n = 4-7 per group) or collagen-induced arthritis (n = 9-15 per group) were injected intravenously with wild-type IL-10 or SA-IL-10, and the retention of SA-IL-10 in the lymph nodes (LNs), immune cell composition in the paws, and therapeutic effect of SA-IL-10 on mice with arthritis were assessed.

RESULTS

SA fusion to IL-10 led to enhanced accumulation in the mouse LNs compared with unmodified IL-10. Intravenous SA-IL-10 treatment restored immune cell composition in the paws to a normal status, elevated the frequency of suppressive alternatively activated macrophages, reduced IL-17A levels in the paw-draining LN, and protected joint morphology. Intravenous SA-IL-10 treatment showed similar efficacy as treatment with an anti-tumor necrosis factor antibody. SA-IL-10 was equally effective when administered intravenously, locally, or subcutaneously, which is a benefit for clinical translation of this molecule.

CONCLUSION

SA fusion to IL-10 is a simple but effective engineering strategy for RA therapy and has potential for clinical translation.

In Sickness and in Health: The Immunological Roles of the Lymphatic System

The lymphatic system plays crucial roles in immunity far beyond those of simply providing conduits for leukocytes and antigens in lymph fluid. Endothelial cells within this vasculature are distinct and highly specialized to perform roles based upon their location. Afferent lymphatic capillaries have unique intercellular junctions for efficient uptake of fluid and macromolecules, while expressing chemotactic and adhesion molecules that permit selective trafficking of specific immune cell subsets. Moreover, in response to events within peripheral tissue such as inflammation or infection, soluble factors from lymphatic endothelial cells exert “remote control” to modulate leukocyte migration across high endothelial venules from the blood to lymph nodes draining the tissue. These immune hubs are highly organized and perfectly arrayed to survey antigens from peripheral tissue while optimizing encounters between antigen-presenting cells and cognate lymphocytes. Furthermore, subsets of lymphatic endothelial cells exhibit differences in gene expression relating to specific functions and locality within the lymph node, facilitating both innate and acquired immune responses through antigen presentation, lymph node remodeling and regulation of leukocyte entry and exit. This review details the immune cell subsets in afferent and efferent lymph, and explores the mechanisms by which endothelial cells of the lymphatic system regulate such trafficking, for immune surveillance and tolerance during steady-state conditions, and in response to infection, acute and chronic inflammation, and subsequent resolution.

The Role of CD4+ Resident Memory T Cells in Local Immunity in the Mucosal Tissue - Protection Versus Pathology

Memory T cells are crucial for both local and systemic protection against pathogens over a long period of time. Three major subsets of memory T cells; effector memory T (T_EM) cells, central memory T (T_CM) cells, and tissue-resident memory T (T_RM) cells have been identified. The most recently identified subset, T_RM cells, is characterized by the expression of the C-type lectin CD69 and/or the integrin CD103. T_RM cells persist locally at sites of mucosal tissue, such as the lung, where they provide frontline defense against various pathogens. Importantly, however, T_RM cells are also involved in shaping the pathology of inflammatory diseases. A number of pioneering studies revealed important roles of CD8⁺ T_RM cells, particularly those in the local control of viral infection. However, the protective function and pathogenic role of CD4⁺ T_RM cells that reside within the mucosal tissue remain largely unknown. In this review, we discuss the ambivalent feature of CD4⁺ T_RM cells in the protective and pathological immune responses. We also review the transcriptional and epigenetic characteristics of CD4⁺ T_RM cells in the lung that have been elucidated by recent technical approaches. A better understanding of the function of CD4⁺ T_RM cells is crucial for the development of both effective vaccination against pathogens and new therapeutic strategies for intractable inflammatory diseases, such as inflammatory bowel diseases and chronic allergic diseases.

Temperature Plays an Essential Regulatory Role in the Tumor Immune Microenvironment

In recent years, emerging immunotherapy has been included in various malignant tumor treatment standards. Temperature has been considered to affect different pathophysiological reactions such as inflammation and cancer for a long time. However, in tumor immunology research, temperature is still rarely considered a significant variable. In this review, we discuss the effects of room temperature, body temperature, and the local tumor temperature on the tumor immune microenvironment from multiple levels and perspectives, and we discuss changes in the body's local and whole-body temperature under tumor conditions. We analyze the current use of ablation treatment-the reason for the opposite immune effect. We should pay more attention to the therapeutic potential of temperature and create a better antitumor microenvironment that can be combined with immunotherapy.

Progression of Metastasis through Lymphatic System

Lymph nodes are the most common sites of metastasis in cancer patients. Nodal disease status provides great prognostic power, but how lymph node metastases should be treated is under debate. Thus, it is important to understand the mechanisms by which lymph node metastases progress and how they can be targeted to provide therapeutic benefits. In this review, we focus on delineating the process of cancer cell migration to and through lymphatic vessels, survival in draining lymph nodes and further spread to other distant organs. In addition, emerging molecular targets and potential strategies to inhibit lymph node metastasis are discussed.

The Dual Role of High Endothelial Venules in Cancer Progression versus Immunity

Secondary lymphoid organs (SLOs) are important initiators and regulators of immunity. To carry out this function, the blood vasculature must deliver oxygen and nutrients and recruit circulating lymphocytes into the SLO parenchyma, where they encounter cognate antigen. High endothelial venules (HEVs) are specialised postcapillary venules that specifically serve this function and are found in all SLOs except spleen. It is becoming clear that alterations to HEV network density and/or morphology can result in immune activation or, as recently implicated, in providing an exit route for tumour cell dissemination and metastases. In this review, the structural plasticity of HEVs, the regulatory pathways underpinning this plasticity, and the relevance of these pathways to cancer progression will be discussed.

Dysregulation of Leukocyte Trafficking in Type 2 Diabetes: Mechanisms and Potential Therapeutic Avenues

Type 2 Diabetes Mellitus (T2DM) is a chronic inflammatory disorder that is characterized by chronic hyperglycemia and impaired insulin signaling which in addition to be caused by common metabolic dysregulations, have also been associated to changes in various immune cell number, function and activation phenotype. Obesity plays a central role in the development of T2DM. The inflammation originating from obese adipose tissue develops systemically and contributes to insulin resistance, beta cell dysfunction and hyperglycemia. Hyperglycemia can also contribute to chronic, low-grade inflammation resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under inflammatory condition is dysregulated in T2DM. We particularly highlight the obesity-related accumulation of leukocytes in the adipose tissue leading to insulin resistance and beta-cell dysfunction and resulting in hyperglycemia and consequent changes of adhesion and migratory behavior of leukocytes in different vascular beds. Thus, here we discuss how potential therapeutic targeting of leukocyte trafficking could be an efficient way to control inflammation as well as diabetes and its vascular complications.

The Role of the IL-33/ST2 Immune Pathway in Autoimmunity: New Insights and Perspectives

Interleukin (IL)-33, a member of IL-1 cytokine family, is produced by various immune cells and acts as an alarm to alert the immune system after epithelial or endothelial cell damage during cell necrosis, infection, stress, and trauma. The biological functions of IL-33 largely depend on its ligation to the corresponding receptor, suppression of tumorigenicity 2 (ST2). The pathogenic roles of this cytokine have been implicated in several disorders, including allergic disease, cardiovascular disease, autoimmune disease, infectious disease, and cancers. However, alerted levels of IL-33 may result in either disease amelioration or progression. Genetic variations of IL33 gene may confer protective or susceptibility risk in the onset of autoimmune diseases. The purpose of this review is to discuss the involvement of IL-33 and ST2 in the pathogenesis of a variety of autoimmune disorders, such as autoimmune rheumatic, neurodegenerative, and endocrine diseases.

Gut-resident CX3CR1hi macrophages induce tertiary lymphoid structures and IgA response in situ

Intestinal mononuclear phagocytes (MPs) are composed of heterogeneous dendritic cell (DC) and macrophage subsets necessary for the initiation of immune response and control of inflammation. Although MPs in the normal intestine have been extensively studied, the heterogeneity and function of inflammatory MPs remain poorly defined. We performed phenotypical, transcriptional, and functional analyses of inflammatory MPs in infectious Salmonella colitis and identified CX3CR1⁺ MPs as the most prevalent inflammatory cell type. CX3CR1⁺ MPs were further divided into three distinct populations, namely, Nos2 ⁺CX3CR1^lo, Ccr7 ⁺CX3CR1^int (lymph migratory), and Cxcl13 ⁺CX3CR1^hi (mucosa resident), all of which were transcriptionally aligned with macrophages and derived from monocytes. In follow-up experiments in vivo, intestinal CX3CR1⁺ macrophages were superior to conventional DC1 (cDC1) and cDC2 in inducing Salmonella-specific mucosal IgA. We next examined spatial organization of the immune response induced by CX3CR1⁺ macrophage subsets and identified mucosa-resident Cxcl13 ⁺CX3CR1^hi macrophages as the antigen-presenting cells responsible for recruitment and activation of CD4⁺ T and B cells to the sites of Salmonella invasion, followed by tertiary lymphoid structure formation and the local pathogen-specific IgA response. Using mice we developed with a floxed Ccr7 allele, we showed that this local IgA response developed independently of migration of the Ccr7 ⁺CX3CR1^int population to the mesenteric lymph nodes and contributed to the total mucosal IgA response to infection. The differential activity of intestinal macrophage subsets in promoting mucosal IgA responses should be considered in the development of vaccines to prevent Salmonella infection and in the design of anti-inflammatory therapies aimed at modulating macrophage function in inflammatory bowel disease.

The Immune Phenotype of Isolated Lymphoid Structures in Non-Tumorous Colon Mucosa Encrypts the Information on Pathobiology of Metastatic Colorectal Cancer

Simple Summary

Today, the presence of well-organized functional structures of immune cells at tumor sites, known as ectopic lymphoid structures, and their strong association with patient survival have been reported in more than ten different cancer types. We aimed to investigate whether there is a link between the patient-specific characteristics of pre-formed isolated lymphoid structures in non-tumorous colon tissue and the disease pathobiology for patients with metastatic colorectal cancer. The study employed a powerful approach of quantitative tissue image cytometry to compare lymphoid structures of different anatomical locations within the same patients. We showed that the properties of isolated lymphoid structures in non-tumorous colon tissue predefine the immune phenotype of ectopic lymphoid structures at primary and metastatic sites. We discovered that B-cell-enriched and highly proliferative lymphoid structures are prognostic towards an improved clinical outcome. The knowledge gained from this study expands our understanding of tumor-immune interactions and draws particular attention to the anti-tumor immune response guided by isolated lymphoid structures outside of tumor tissue.

Abstract

The gut-associated lymphoid tissue represents an integral part of the immune system. Among the powerful players of the mucosa-associated lymphoid tissue are isolated lymphoid structures (ILSs), which as information centers, drive the local (and systemic) adaptive immune responses. Germinal center reactions, taking place within ILSs, involve the coordinated action of various immune cell types with a central role given to B cells. In the current study, we aimed at dissecting the impact of ILSs within non-tumorous colon tissue (NT) on the pathobiology of colorectal cancer (CRC) with metastasis in the liver (CRCLM). In particular, we focused on the immune phenotypes of ILSs and ectopic lymphoid structures (ELSs), built up at matching primary and metastatic tumor sites. We implemented an integrative analysis strategy on the basis of tissue image cytometry and clonality assessment to explore the immune phenotype of ILS/ELS at three tissue entities: NT, CRC, and CRCLM (69 specimens in total). Applying a panel of lineage markers used for immunostaining, we characterized and compared the anatomical features, the cellular composition, the activation, and proliferation status of ILSs and ELSs, and assessed the clinical relevance of staining-derived data sets. Our major discovery was that ILS characteristics at the NT site predefine the immune phenotype of ELSs at CRC and CRCLM. Thereby, B-cell-enriched (CD20) and highly proliferative (Ki67) ILSs and ELSs were found to be associated with improved clinical outcome in terms of survival and enabled patient stratification into risk groups. Moreover, the data revealed a linkage between B-cell clonality at the NT site and the metastatic characteristics of the tumor in the distant liver tissue. Consolidation of immunostaining-based findings with the results of compendium-wide transcriptomic analysis furthermore proposed CD27 as a novel marker of T follicular helper cells within lymphoid structures. Overall, the study nominates the ILS immune phenotype as a novel prognostic marker for patients with metastatic CRC.

Prolonged residence of an albumin-IL-4 fusion protein in secondary lymphoid organs ameliorates experimental autoimmune encephalomyelitis

Interleukin-4 (IL-4) suppresses the development of multiple sclerosis in a murine model of experimental autoimmune encephalomyelitis (EAE). Here, we show that, in mice with EAE, the accumulation and persistence in the lymph nodes and spleen of a systemically administered serum albumin (SA)-IL-4 fusion protein leads to higher efficacy in preventing disease development than the administration of wild-type IL-4 or of the clinically approved drug fingolimod. We also show that the SA-IL-4 fusion protein prevents immune-cell infiltration in the spinal cord, decreases integrin expression in antigen-specific CD4⁺ T cells, increases the number of granulocyte-like myeloid-derived suppressor cells (and their expression of programmed-death-ligand-1) in spinal cord-draining lymph nodes and decreases the number of T helper 17 cells, a pathogenic cell population in EAE. In mice with chronic EAE, SA-IL-4 inhibits immune-cell infiltration into the spinal cord and completely abrogates immune responses to myelin antigen in the spleen. The SA-IL-4 fusion protein may be prophylactically and therapeutically advantageous in the treatment of multiple sclerosis.

Temporal analysis of the bovine lymph node transcriptome during cattle tick (Rhipicephalus microplus) infestation

Livestock production is a fundamental source of revenue and nutrition, wherein cattle-farming constitutes one of the major agricultural industries. Vectors and vector-borne diseases constitute one of the major factors that decrease the livelihood of all farming communities, more so in resource-poor communities and developing countries. Understanding the immunological responses during tick infestation in cattle is instrumental in the development of novel and improved tick control strategies, such as vaccines. In this study, gene expression patterns were compared within the lymph nodes of three cattle breeds at different life stages of the cattle tick, Rhipicephalus microplus. For Bonsmara (5/8Bos taurus indicus × 3/8B. t. taurus) cattle specifically, some 183 genes were found to be differentially expressed within the lymph nodes during larval and adult tick feeding, relative to uninfested cattle. Overall, the data provides evidence for a transcriptional regulatory network that is activated during immature tick infestation, but is down-regulated towards basal transcriptional levels when adult ticks are feeding. Specific processes in the lymph nodes of Bonsmara cattle were found to be differentially regulated on a transcriptional level. These include: (1) Leukocyte recruitment to the lymph node via chemokines and chemotaxis, (2) Trans-endothelial and intranodal movement on the reticular network, (3) Active regulation of cellular transcription and translation in the lymph node (including leukocyte associated cellular regulatory networks) and (4) Chemokine receptors regulating the movement of cells out of the lymph node. This work provides a first transcriptome analysis of bovine lymph node responses in tick-infested cattle. Findings show a dynamic immune response to tick infestation for the Bonsmara cattle breed, and that suppression of the maturation of the cattle hosts' immunity is especially evident during the larval feeding stages.

Formin-like 1 mediates effector T cell trafficking to inflammatory sites to enable T cell-mediated autoimmunity

Lymphocyte migration is essential for the function of the adaptive immune system, and regulation of T cell entry into tissues is an effective therapy in autoimmune diseases. Little is known about the specific role of cytoskeletal effectors that mediate mechanical forces and morphological changes essential for migration in complex environments. We developed a new Formin-like-1 (FMNL1) knock-out mouse model and determined that the cytoskeletal effector FMNL1 is selectively required for effector T cell trafficking to inflamed tissues, without affecting naïve T cell entry into secondary lymphoid organs. Here, we identify a FMNL1-dependent mechanism of actin polymerization at the back of the cell that enables migration of the rigid lymphocyte nucleus through restrictive barriers. Furthermore, FMNL1-deficiency impairs the ability of self-reactive effector T cells to induce autoimmune disease. Overall, our data suggest that FMNL1 may be a potential therapeutic target to specifically modulate T cell trafficking to inflammatory sites.

In situ thermal ablation augments antitumor efficacy of adoptive T cell therapy

Purpose: The aim of this study is to investigate whether radiofrequency ablation (RFA) improves the efficacy of adoptive T cell immunotherapy in preclinical mouse cancer models.Method: Mice implanted subcutaneously (sc) with syngeneic colon adenocarcinoma or melanoma were treated with sub-curative in situ RFA (90 °C, 1 min). Trafficking of T cells to lymph nodes (LN) or tumors was quantified by homing assays and intravital microscopy (IVM) after sham procedure or RFA. Expression of trafficking molecules (CCL21 and intercellular adhesion molecule-1 [ICAM-1]) on high endothelial venules (HEV) in LN and tumor vessels was evaluated by immunofluorescence microscopy. Tumor-bearing mice were pretreated with RFA to investigate the therapeutic benefit when combined with adoptive transfer of in vitro-activated tumor-specific CD8⁺ T cells.Results: RFA increased trafficking of naïve CD8⁺ T cells to tumor-draining LN (TdLN). A corresponding increase in expression of ICAM-1 and CCL21 was detected on HEV in TdLN but not in contralateral (c)LN. IVM revealed that RFA substantially enhanced secondary firm arrest of lymphocytes selectively in HEV in TdLN. Furthermore, strong induction of ICAM-1 in tumor vessels was associated with significantly augmented trafficking of adoptively transferred in vitro-activated CD8⁺ T cells to tumors after RFA. Finally, preconditioning tumors with RFA augmented CD8⁺ T cell-mediated apoptosis of tumor targets and delayed growth of established tumors when combined with adoptive T cell transfer immunotherapy.Conclusions: These studies suggest that in addition to its role as a palliative therapeutic modality, RFA may have clinical potential as an immune-adjuvant therapy by augmenting the efficacy of adoptive T cell therapy.

Stromal cell control of conventional and ectopic germinal centre reactions

The germinal centre (GC) is a specialized cellular structure that forms in response to antigenic stimulation. It generates long-term humoral immunity through the production of memory B cells and long-lived antibody-secreting plasma cells. Conventional GCs form within secondary lymphoid organs, where networks of specialised stromal cells that form during embryogenesis act as the stage upon which the various GC immune cell players are brought together, nurtured and co-ordinated to generate a productive response. In non-lymphoid organs, ectopic GCs can form in response to persistent antigenic and inflammatory stimuli. Unlike secondary lymphoid tissues, non-lymphoid organs do not have a developmentally programmed stromal cell network capable of supporting the germinal centre reaction; therefore, the local tissue stroma must be remodelled by inflammatory stimuli in order to host a GC reaction. These ectopic GCs produce memory B cells and plasma cells that form a critical component of the humoral immune response.

Robo4 contributes to the turnover of Peyer's patch B cells

All leukocytes can get entrance into the draining lymph nodes via the afferent lymphatics but only lymphoid cells can leave the nodes. The molecular mechanisms behind this phenomenon have remained unknown. We employed genome wide microarray analyses of the subcapsular sinus and lymphatic sinus (LS) endothelial cells and found Robo4 to be selectively expressed on LS lymphatics. Further analyses showed high Robo4 expression in lymphatic vessels of Peyer's patches, which only have efferent lymphatic vessels. In functional assays, Robo4-deficient animals showed accumulation of naïve  B cells (CD19⁺/CD62L^hi/CD44^lo) in Peyer's patches, whereas no difference was seen within other lymphocyte subtypes. Short-term lymphocyte homing via high endothelial venules to peripheral and mesenteric lymph nodes and Peyer's patches was also slightly impaired in Robo4 knockout animals. These results show for the first time, selective expression of Robo4 in the efferent arm of the lymphatics and its role in controlling the turnover of a subset of B lymphocytes from Peyer's patches.

Regulation of global CD8+ T-cell positioning by the actomyosin cytoskeleton

CD8⁺ T cells have evolved as one of the most motile mammalian cell types, designed to continuously scan peptide-major histocompatibility complexes class I on the surfaces of other cells. Chemoattractants and adhesion molecules direct CD8⁺ T-cell homing to and migration within secondary lymphoid organs, where these cells colocalize with antigen-presenting dendritic cells in confined tissue volumes. CD8⁺ T-cell activation induces a switch to infiltration of non-lymphoid tissue (NLT), which differ in their topology and biophysical properties from lymphoid tissue. Here, we provide a short overview on regulation of organism-wide trafficking patterns during naive T-cell recirculation and their switch to non-lymphoid tissue homing during activation. The migratory lifestyle of CD8⁺ T cells is regulated by their actomyosin cytoskeleton, which translates chemical signals from surface receptors into mechanical work. We explore how properties of the actomyosin cytoskeleton and its regulators affect CD8⁺ T cell function in lymphoid and non-lymphoid tissue, combining recent findings in the field of cell migration and actin network regulation with tissue anatomy. Finally, we hypothesize that under certain conditions, intrinsic regulation of actomyosin dynamics may render NLT CD8⁺ T-cell populations less dependent on input from extrinsic signals during tissue scanning.

Characterization of the Dynamic Behavior of Neutrophils Following Influenza Vaccination

Neutrophils are amongst the first cells to respond to inflammation and infection. Although they play a key role in limiting the dissemination of pathogens, the study of their dynamic behavior in immune organs remains elusive. In this work, we characterized in vivo the dynamic behavior of neutrophils in the mouse popliteal lymph node (PLN) after influenza vaccination with UV-inactivated virus. To achieve this, we used an image-based systems biology approach to detect the motility patterns of neutrophils and to associate them to distinct actions. We described a prominent and rapid recruitment of neutrophils to the PLN following vaccination, which was dependent on the secretion of the chemokine CXCL1 and the alarmin molecule IL-1α. In addition, we observed that the initial recruitment occurred mainly via high endothelial venules located in the paracortical and interfollicular regions of the PLN. The analysis of the spatial-temporal patterns of neutrophil migration demonstrated that, in the initial stage, the majority of neutrophils displayed a patrolling behavior, followed by the formation of swarms in the subcapsular sinus of the PLN, which were associated with macrophages in this compartment. Finally, we observed using multiple imaging techniques, that neutrophils phagocytize and transport influenza virus particles. These processes might have important implications in the capacity of these cells to present viral antigens.

High-endothelial cell-derived S1P regulates dendritic cell localization and vascular integrity in the lymph node

While the sphingosine-1-phosphate (S1P)/sphingosine-1-phosphate receptor-1 (S1PR1) axis is critically important for lymphocyte egress from lymphoid organs, S1PR1-activation also occurs in vascular endothelial cells (ECs), including those of the high-endothelial venules (HEVs) that mediate lymphocyte immigration into lymph nodes (LNs). To understand the functional significance of the S1P/S1PR1-G_i axis in HEVs, we generated Lyve1;Spns2^Δ/Δ conditional knockout mice for the S1P-transporter Spinster-homologue-2 (SPNS2), as HEVs express LYVE1 during development. In these mice HEVs appeared apoptotic and were severely impaired in function, morphology and size; leading to markedly hypotrophic peripheral LNs. Dendritic cells (DCs) were unable to interact with HEVs, which was also observed in Cdh5^CRE-ERT2;S1pr1^Δ/Δ mice and wildtype mice treated with S1PR1-antagonists. Wildtype HEVs treated with S1PR1-antagonists in vitro and Lyve1-deficient HEVs show severely reduced release of the DC-chemoattractant CCL21 in vivo. Together, our results reveal that EC-derived S1P warrants HEV-integrity through autocrine control of S1PR1-G_i signaling, and facilitates concomitant HEV-DC interactions.

Engineering Cell Membrane-Based Nanotherapeutics to Target Inflammation

Inflammation is ubiquitous in the body, triggering desirable immune response to defend against dangerous signals or instigating undesirable damage to cells and tissues to cause disease. Nanomedicine holds exciting potential in modulating inflammation. In particular, cell membranes derived from cells involved in the inflammatory process may be used to coat nanotherapeutics for effective targeted delivery to inflammatory tissues. Herein, the recent progress of rationally engineering cell membrane-based nanotherapeutics for inflammation therapy is highlighted, and the challenges and opportunities presented in realizing the full potential of cell-membrane coating in targeting and manipulating the inflammatory microenvironment are discussed.

Soluble CLEC-2 is generated independently of ADAM10 and is increased in plasma in acute coronary syndrome: comparison with soluble GPVI

Soluble forms of platelet membrane proteins are released upon platelet activation. We previously reported that soluble C-type lectin-like receptor 2 (sCLEC-2) is released as a shed fragment (Shed CLEC-2) or as a whole molecule associated with platelet microparticles (MP-CLEC-2). In contrast, soluble glycoprotein VI (sGPVI) is released as a shed fragment (Shed GPVI), but not as a microparticle-associated form (MP-GPVI). However, mechanism of sCLEC-2 generation or plasma sCLEC-2 has not been fully elucidated. Experiments using metalloproteinase inhibitors/stimulators revealed that ADAM10/17 induce GPVI shedding, but not CLEC-2 shedding, and that shed CLEC-2 was partially generated by MMP-2. Although MP-GPVI was not generated, it was generated in the presence of the ADAM10 inhibitor. Moreover, antibodies against the cytoplasmic or extracellular domain of GPVI revealed the presence of the GPVI cytoplasmic domain, but not the extracellular domain, in the microparticles. These findings suggest that most of the GPVI on microparticles are induced to shed by ADAM10; MP-GPVI is thus undetected. Plasma sCLEC-2 level was 1/32 of plasma sGPVI level in normal subjects, but both soluble proteins significantly increased in plasma of patients with acute coronary syndrome. Thus, sCLEC-2 and sGPVI are released by different mechanisms and released in vivo upon platelet activation.

Material design for lymph node drug delivery

A significant fraction of the total immune cells in the body are located in several hundred lymph nodes, in which lymphocyte accumulation, activation and proliferation are organized. Therefore, targeting lymph nodes provides the possibility to directly deliver drugs to lymphocytes and lymph node-resident cells and thus to modify the adaptive immune response. However, owing to the structure and anatomy of lymph nodes, as well as the distinct localization and migration of the different cell types within the lymph node, it is difficult to access specific cell populations by delivering free drugs. Materials can be used as instructive delivery vehicles to achieve accumulation of drugs in the lymph nodes and to target specific lymph node-resident cell subtypes. In this Review, we describe the compartmental architecture of lymph nodes and the cell and fluid transport mechanisms to and from lymph nodes. We discuss the different entry routes into lymph nodes and how they can be explored for drug delivery, including the lymphatics, blood capillaries, high endothelial venules, cell-mediated pathways, homing of circulating lymphocytes and direct lymph node injection. We examine different nanoscale and microscale materials for the targeting of specific immune cells and highlight their potential for the treatment of immune dysfunction and for cancer immunotherapy. Finally, we give an outlook to the field, exploring how lymph node targeting can be improved by the use of materials.

Lymphatic Migration of Immune Cells

Lymphatic vessels collect interstitial fluid that has extravasated from blood vessels and return it to the circulatory system. Another important function of the lymphatic network is to facilitate immune cell migration and antigen transport from the periphery to draining lymph nodes. This migration plays a crucial role in immune surveillance, initiation of immune responses and tolerance. Here we discuss the significance and mechanisms of lymphatic migration of innate and adaptive immune cells in homeostasis, inflammation and cancer.

Clever-1 contributes to lymphocyte entry into the spleen via the red pulp

Lymphocytes recirculate continuously between the blood and lymphoid organs, a process that is of fundamental importance for proper functioning of the immune system. The molecular mechanisms underlying lymphocyte trafficking to the spleen remain an enigma. Here, we show that lymphocytes enter the spleen preferentially from vessels in the red pulp rather than the marginal sinus or the vasculature in the white pulp. Ex vivo adhesion assays in mice and humans, together with genetic ablation of Clever-1 in mice, indicate that CD8+T cell and B220+B cell homing to the spleen via the red pulp is Clever-1 dependent. Moreover, absence of Clever-1 leads to down-regulation of the B cell attractant chemokine, CXCL13, on spleen endothelium. CXCL13 is known to guide B cell trafficking to lymphoid organs, and its lack may contribute to the observed decrease in B cell trafficking into the spleen as well. In summary, this study identifies Clever-1 as an important molecule controlling lymphocyte entry into the spleen, along with a critical role for the splenic red pulp in this regulated trafficking. Furthermore, the results demonstrate that location-specific homing-associated molecules guide lymphocyte entry into the spleen.

Lymphatic endothelial cells regulate B-cell homing to lymph nodes via a NIK-dependent mechanism

B cells home to the lymph nodes (LNs) via high endothelial venules (HEVs) under the guidance of chemokines, particularly CXCL13. However, as CXCL13 is not directly made in HEVs, the molecular mechanism mediating B-cell homing to LNs has remained unclear. We show here that nuclear factor (NF)-κB-inducing kinase (NIK), a kinase mediating activation of the noncanonical NF-κB pathway, functions in lymphatic endothelial cells (LECs) to regulate B-cell homing to LNs. LEC-conditional deletion of NIK in mice did not affect the integrity or global function of lymphatic vessels but caused a severe reduction in the frequency of B cells in LNs. The LEC-specific NIK deficiency did not affect the survival of B cells or the frequency of B cells in the spleen. B-cell adoptive transfer studies revealed that the LEC-specific NIK deletion impairs the ability of LNs to recruit B cells. We further show that NIK mediates expression of the chemokines CXCL13 and CCL19 in LECs. Although CCL19 is also expressed in blood endothelial cells (BECs), CXCL13 is not produced in BECs. These results suggest that NIK regulates naive B-cell homing to LNs via mediating production of the B-cell homing chemokine CXCL13 in LECs.

Comparative Transcriptomic Analysis Identifies a Range of Immunologically Related Functional Elaborations of Lymph Node Associated Lymphatic and Blood Endothelial Cells

Lymphatic and blood vessels are formed by specialized lymphatic endothelial cells (LEC) and blood endothelial cells (BEC), respectively. These endothelial populations not only form peripheral tissue vessels, but also critical supporting structures in secondary lymphoid organs, particularly the lymph node (LN). Lymph node LEC (LN-LEC) also have been shown to have important immunological functions that are not observed in LEC from tissue lymphatics. LN-LEC can maintain peripheral tolerance through direct presentation of self-antigen via MHC-I, leading to CD8 T cell deletion; and through transfer of self-antigen to dendritic cells for presentation via MHC-II, resulting in CD4 T cell anergy. LN-LEC also can capture and archive foreign antigens, transferring them to dendritic cells for maintenance of memory CD8 T cells. The molecular basis for these functional elaborations in LN-LEC remain largely unexplored, and it is also unclear whether blood endothelial cells in LN (LN-BEC) might express similar enhanced immunologic functionality. Here, we used RNA-Seq to compare the transcriptomic profiles of freshly isolated murine LEC and BEC from LN with one another and with freshly isolated LEC from the periphery (diaphragm). We show that LN-LEC, LN-BEC, and diaphragm LEC (D-LEC) are transcriptionally distinct from one another, demonstrating both lineage and tissue-specific functional specializations. Surprisingly, tissue microenvironment differences in gene expression profiles were more numerous than those determined by endothelial cell lineage specification. In this regard, both LN-localized endothelial cell populations show a variety of functional elaborations that suggest how they may function as antigen presenting cells, and also point to as yet unexplored roles in both positive and negative regulation of innate and adaptive immune responses. The present work has defined in depth gene expression differences that point to functional specializations of endothelial cell populations in different anatomical locations, but especially the LN. Beyond the analyses provided here, these data are a resource for future work to uncover mechanisms of endothelial cell functionality.

Regulation of the Germinal Center Response

The germinal center (GC) is a specialized microstructure that forms in secondary lymphoid tissues, producing long-lived antibody secreting plasma cells and memory B cells, which can provide protection against reinfection. Within the GC, B cells undergo somatic mutation of the genes encoding their B cell receptors which, following successful selection, can lead to the emergence of B cell clones that bind antigen with high affinity. However, this mutation process can also be dangerous, as it can create autoreactive clones that can cause autoimmunity. Because of this, regulation of GC reactions is critical to ensure high affinity antibody production and to enforce self-tolerance by avoiding emergence of autoreactive B cell clones. A productive GC response requires the collaboration of multiple cell types. The stromal cell network orchestrates GC cell dynamics by controlling antigen delivery and cell trafficking. T follicular helper (Tfh) cells provide specialized help to GC B cells through cognate T-B cell interactions while Foxp3⁺ T follicular regulatory (Tfr) cells are key mediators of GC regulation. However, regulation of GC responses is not a simple outcome of Tfh/Tfr balance, but also involves the contribution of other cell types to modulate the GC microenvironment and to avoid autoimmunity. Thus, the regulation of the GC is complex, and occurs at multiple levels. In this review we outline recent developments in the biology of cell subsets involved in the regulation of GC reactions, in both secondary lymphoid tissues, and Peyer's patches (PPs). We discuss the mechanisms which enable the generation of potent protective humoral immunity whilst GC-derived autoimmunity is avoided.

MyD88 signaling causes autoimmune sialadenitis through formation of high endothelial venules and upregulation of LTβ receptor-mediated signaling

Autoimmune sialadenitis (AS), chronic inflammation of the salivary glands (SGs) with focal lymphocyte infiltration, appears in autoimmune diseases such as Sjӧgren’s syndrome. The pathological role of MyD88-dependent innate immune signaling in autoimmune diseases including AS has been studied using mouse models, such as NOD mice. Although AS development in NOD mice was reported to be suppressed by Myd88 deficiency, its specific role remains unclear. Here, we determined the potent suppressive effects of Myd88 deficiency on AS development in lupus-prone B6/lpr mice, which have lymphoproliferation abnormalities, and also in NOD mice, which have no lymphoproliferation abnormalities. This indicates that MyD88 signaling triggers AS through both lymphoproliferation-dependent and -independent mechanisms. To address the MyD88-dependent lymphoproliferation-independent AS manifestation, SGs from C57BL/6 mice were analyzed. Remarkable upregulation of Glycam1 and high endothelial venule (HEV)-associated changes were unexpectedly found in Myd88^+/+ mice, compared with Myd88^−/− mice. MyD88-dependent HEV-associated changes were also observed in NOD mice. Additionally, Lta, Ltb, and Ltbr in SGs of NOD mice were lowered by Myd88 deficiency. Interestingly, LTβR-induced HEV-associated gene expression in cultured cells was impaired by Myd88 deficiency. Our findings highlight novel roles for MyD88 in AS development, which imply the existence of MyD88-dependent HEV formation in ectopic lymphoid neogenesis.