Viral infection prevents diabetes by inducing regulatory T cells through NKT cell-plasmacytoid dendritic cell interplay

Increased tumor-infiltrating plasmacytoid dendritic cells express high levels of PD-L2 and affect CD8+ T lymphocyte infiltration in human laryngeal squamous cell carcinoma

The infiltration and prognostic significance of tumor-infiltrating plasmacytoid dendritic cells (TI-pDC) have been elucidated in various human solid cancers. However, the infiltrating patterns and functional importance of TI-pDC in laryngeal squamous cell carcinoma (LSCC) remain unknown. In this study, flow cytometric analyses were conducted to characterize the infiltration of dendritic cells and T lymphocytes, along with their respective subgroups in tumor tissues (TT), para-carcinoma tissues (PT), and peripheral blood (PB) from LSCC patients. Immunohistochemical staining for CD4 and CD8, as well as immunofluorescence staining for CD123, were performed on serial tissue sections to investigate the co-localization of TI-pDC and tumor-infiltrating T lymphocytes (TIL) within the tumor microenvironment (TME). Our results demonstrated significantly lower percentages of all three DC subsets in PB compared to TT and PT. Notably, the pDC percentage was markedly higher in TT than in PT. Moreover, TI-pDC percentage was significantly elevated in N+ stage patients compared to those with N0 stage. The results of survival analysis consistently demonstrated that high levels of TI-pDC infiltration were indicative of a poor prognosis. Further investigation revealed a significant negative correlation between TI-pDC and CD8+ TILs; notably, pDCs expressed an inhibitory surface molecule PD-L2 rather than PD-L1 within PT. Collectively, our findings suggest that increased TI-pDC is associated with adverse outcomes in LSCC patients while exhibiting an inhibitory phenotype that may play a crucial role in suppressing CD8+ TILs within LSCC tumors. These results highlight the potential therapeutic strategy targeting PD-L2+ pDCs for immunotherapies against LSCC.

The Multifaceted Functionality of Plasmacytoid Dendritic Cells in Gastrointestinal Cancers: A Potential Therapeutic Target?

Gastrointestinal (GI) tumors pose a significant global health burden, necessitating the exploration of novel therapeutic approaches. Plasmacytoid dendritic cells (pDCs) play a crucial role in tumor immunity, exhibiting both anti-tumor and pro-tumor effects. This review aims to summarize the role of pDCs in different types of GI tumors and assess their potential as therapeutic targets. In gastric cancer, hepatocellular carcinoma, and intrahepatic cholangiocarcinoma, increased infiltration of pDCs was associated with a worse outcome, whereas in esophageal cancer, pancreatic cancer, and colorectal cancer, pDC infiltration improved the outcome. Initial animal studies of gastric cancer and hepatocellular carcinoma showed that pDCs could be a successful therapeutic target. In conclusion, pDCs play a multifaceted role in GI tumors, influencing both anti-tumor immunity and tumor progression. Further research is needed to optimize their clinical application and explore combinatorial approaches.

The role of plasmacytoid dendritic cells (pDCs) in immunity during viral infections and beyond

Type I and III interferons (IFNs) are essential for antiviral immunity and act through two different but complimentary pathways. First, IFNs activate intracellular antimicrobial programs by triggering the upregulation of a broad repertoire of viral restriction factors. Second, IFNs activate innate and adaptive immunity. Dysregulation of IFN production can lead to severe immune system dysfunction. It is thus crucial to identify and characterize the cellular sources of IFNs, their effects, and their regulation to promote their beneficial effects and limit their detrimental effects, which can depend on the nature of the infected or diseased tissues, as we will discuss. Plasmacytoid dendritic cells (pDCs) can produce large amounts of all IFN subtypes during viral infection. pDCs are resistant to infection by many different viruses, thus inhibiting the immune evasion mechanisms of viruses that target IFN production or their downstream responses. Therefore, pDCs are considered essential for the control of viral infections and the establishment of protective immunity. A thorough bibliographical survey showed that, in most viral infections, despite being major IFN producers, pDCs are actually dispensable for host resistance, which is achieved by multiple IFN sources depending on the tissue. Moreover, primary innate and adaptive antiviral immune responses are only transiently affected in the absence of pDCs. More surprisingly, pDCs and their IFNs can be detrimental in some viral infections or autoimmune diseases. This makes the conservation of pDCs during vertebrate evolution an enigma and thus raises outstanding questions about their role not only in viral infections but also in other diseases and under physiological conditions.

Therapeutic induction of antigen-specific immune tolerance

The development of therapeutic approaches for the induction of robust, long-lasting and antigen-specific immune tolerance remains an important unmet clinical need for the management of autoimmunity, allergy, organ transplantation and gene therapy. Recent breakthroughs in our understanding of immune tolerance mechanisms have opened new research avenues and therapeutic opportunities in this area. Here, we review mechanisms of immune tolerance and novel methods for its therapeutic induction.

Innate immune cells: Key players of orchestra in modulating tumor microenvironment (TME)

The tumor microenvironment (TME) with vital role in cancer progression is composed of various cells such as endothelial cells, immune cells, and mesenchymal stem cells. In particular, innate immune cells such as macrophages, dendritic cells, myeloid-derived suppressor cells, neutrophils, innate lymphoid cells, γδT lymphocytes, and natural killer cells can either promote or suppress tumor progression when present in the TME. An increase in research on the cross-talk between the TME and innate immune cells will lead to new approaches for anti-tumoral therapeutic interventions. This review primarily focuses on the biology of innate immune cells and their main functions in the TME. In addition, it summarizes several innate immune-based immunotherapies that are currently tested in clinical trials.

Tregs protect against invariant NKT cell-mediated autoimmune colitis and hepatitis

Immunomodulatory T cells play a pivotal role in protection against (auto)immune-mediated diseases that open perspectives for therapeutic modulation. However, how immune regulatory networks operate in vivo is less understood. To this end, we focused on FOXP3+CD4+CD25+ regulatory T cells (Tregs) and invariant natural killer T (iNKT) cells, two lymphocyte populations that independently regulate adaptive and innate immune responses. In vitro, a functional interplay between Tregs and iNKT cells has been described, but whether Tregs modulate the function and phenotype of iNKT cell subsets in vivo and whether this controls iNKT-mediated autoimmunity is unclear. Taking advantage of the conditional depletion of Tregs, we examined the in vivo interplay between iNKT and Treg cells in steady state and in preclinical models of liver and gut autoimmunity. Under non-inflamed conditions, Treg depletion enhanced glycolipid-mediated iNKT cell responses, with a general impact on Type 1, 2 and 17 iNKT subsets. Moreover, in vivo iNKT activation in the absence of Tregs suppressed the induction of iNKT anergy, consistent with a reduction in programmed cell death receptor 1 (PD-1) expression. Importantly, we unveiled a clear role for an in vivo Treg-iNKT crosstalk both in concanavalin A-induced acute hepatitis and oxazolone-induced colitis. Here, the absence of Tregs led to a markedly enhanced liver and gut pathology, which was not observed in iNKT-deficient mice. Taken together, these results provide evidence for a functional interplay between regulatory T cell subsets critical in controlling the onset of autoimmune disease.

NKT-Licensed In Vivo Dendritic Cell-Based Immunotherapy as Cellular Immunodrugs for Cancer Treatment

With the advent of new therapies, immunotherapy has gained attention as a critical modality. After the discovery of the natural killer T (NKT) cells ligand, ex vivo cultured dendritic cells (DCs) loaded with NKT ligand (especially α-galactosylceramide (α-GalCer) (DC/Gal) or ex vivo expanded NKT transfer studies were clinically examined in several institutes. To prevent tumoral immune escape, the link between innate and adaptive immunity, in situ selective targeting of DCs has been attempted; however, protocol optimization was required. As a type of DC targeting therapy that combines the benefits of invariant natural killer T (iNKT) cells, we established an all-in-one, off-the-shelf drug, named the artificial adjuvant vector cell (aAVC), which consists of the tumor antigen and the CD1d-iNKT ligand complex. Here, to our knowledge, we first demonstrate the DC/GalCer therapy and NKT transfer therapy. Next, we introduce and discuss the use of aAVC therapy not only for efficient innate and adaptive immunity induction using fully matured DC in situ but also the characterization necessary for locally reprogramming the tumor microenvironment and systemically inducing long-term memory in T cells. We also discuss how the immune network mechanism is controlled by DCs. Next, we performed the first human clinical trial using WT1 antigen-expressing aAVC against relapse and refractory acute myelogenous leukemia. Thus, we highlight the challenges of using aAVCs as prodrugs for actively energizing DCs in vivo, underpinning immunological networks, and developing strategies for providing maximal benefits for patients.

Preclinical models for Type 1 Diabetes Mellitus - A practical approach for research

Numerous preclinical models have been developed to advance biomedical research in type 1 diabetes mellitus (T1DM). They are essential for improving our knowledge of T1DM development and progression, allowing researchers to identify potential therapeutic targets and evaluate the effectiveness of new medications. A deeper comprehension of these models themselves is critical not only to determine the optimal strategies for their utilization but also to fully unlock their potential applications in both basic and translational research. Here, we will comprehensively summarize and discuss the applications, advantages, and limitations of the commonly used animal models for human T1DM and also overview the up-to-date human tissue bioengineering models for the investigation of T1DM. By combining these models with a better understanding of the pathophysiology of T1DM, we can enhance our insights into disease initiation and development, ultimately leading to improved therapeutic responses and outcomes.

The role of innate immune cells in the tumor microenvironment and research progress in anti-tumor therapy

Innate immune cells in the tumor microenvironment (TME) mainly include macrophages, neutrophils, natural killer cells, dendritic cells and bone marrow derived suppressor cells. They play an anti-tumor or pro-tumor role by secreting various cytokines, chemokines and other factors, and determine the occurrence and development of tumors. Comprehending the role of innate immune cells in tumorigenesis and progression can help improve therapeutic approaches targeting innate immune cells in the TME, increasing the likelihood of favorable prognosis. In this review, we discussed the cell biology of innate immune cells, their role in tumorigenesis and development, and the current status of innate immune cell-based immunotherapy, in order to provide an overview for future research lines and clinical trials.

Multiple immune function impairments in diabetic patients and their effects on COVID-19

Coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2, poses a significant threat to public health worldwide, and diabetes is considered a risk factor for the rapid progression and poor prognosis of COVID-19. Limited immune function is a clinical feature of COVID-19 patients, and diabetes patients have defects in innate and adaptive immune functions, which may be an important reason for the rapid progression and poor prognosis of COVID-19 in patients with diabetes. We review the possible multiple effects of immune impairment in diabetic patients on the immune responses to COVID-19 to provide guidance for the diagnosis and treatment of diabetic patients with COVID-19.

Natural Killer Cells as Key Mediators in Type I Diabetes Immunopathology

The immunopathology of type I diabetes (T1D) presents a complicated case in part because of the multifactorial origin of this disease. Typically, T1D is thought to occur as a result of autoimmunity toward islets of Langerhans, resulting in the destruction of insulin-producing cells (β cells) and thus lifelong reliance on exogenous insulin. However, that explanation obscures much of the underlying mechanism, and the actual precipitating events along with the associated actors (latent viral infection, diverse immune cell types and their roles) are not completely understood. Notably, there is a malfunctioning in the regulation of cytotoxic CD8+ T cells that target endocrine cells through antigen-mediated attack. Further examination has revealed the likelihood of an imbalance in distinct subpopulations of tolerogenic and cytotoxic natural killer (NK) cells that may be the catalyst of adaptive immune system malfunction. The contributions of components outside the immune system, including environmental factors such as chronic viral infection also need more consideration, and much of the recent literature investigating the origins of this disease have focused on these factors. In this review, the details of the immunopathology of T1D regarding NK cell disfunction is discussed, along with how those mechanisms stand within the context of general autoimmune disorders. Finally, the rarer cases of latent autoimmune, COVID-19 (viral), and immune checkpoint inhibitor (ICI) induced diabetes are discussed as their exceptional pathology offers insight into the evolution of the disease as a whole.

Toll-like receptor-9 stimulated plasmacytoid dendritic cell precursors suppress autoimmune neuroinflammation in a murine model of multiple sclerosis

Early innate education of hematopoietic progenitors within the bone marrow (BM) stably primes them for either trained immunity or instead immunoregulatory functions. We herein demonstrate that in vivo or in vitro activation within the BM via Toll-like receptor-9 generates a population of plasmacytoid dendritic cell (pDC) precursors (CpG-pre-pDCs) that, unlike pDC precursors isolated from PBS-incubated BM (PBS-pre-pDCs), are endowed with the capacity to halt progression of ongoing experimental autoimmune encephalomyelitis. CpG activation enhances the selective migration of pDC precursors to the inflamed spinal cord, induces their immediate production of TGF-β, and after migration, of enhanced levels of IL-27. CpG-pre-pDC derived TGF-β and IL-27 ensure protection at early and late phases of the disease, respectively. Spinal cords of CpG-pre-pDC-protected recipient mice display enhanced percentages of host-derived pDCs expressing TGF-β as well as an accumulation of IL-10 producing B cells and of CD11c⁺ CD11b⁺ dendritic cells. These results reveal that pDC precursors are conferred stable therapeutic properties by early innate activation within the BM. They further extend to the pDC lineage promising perspectives for cell therapy of autoimmune diseases with innate activated hematopoietic precursor cells.

Dendritic cells in the tumor microenvironment: prognostic and theranostic impact

Among all immune cells, dendritic cells (DC) are the most potent APCs in the immune system and are central players of the adaptive immune response. There are phenotypically and functionally distinct DC populations derived from blood and lymphoid organ including plasmacytoid DC (pDC), conventional DC (cDC1 and cDC2) and monocyte-derived DC (moDC). The interaction between these different DCs and tumors is a dynamic process where DC-mediated cross-priming of tumor specific T cells is critical in initiating and sustaining anti-tumor immunity. Their presence within the tumor tends to induce T cell responses and to reduce cancer progression and is associated with improved patient survival. This review will focus on the distinct tumor-associated DCs (TADC) subsets in the tumor microenvironment (TME), their roles in tumor immunology and their prognostic and/or predictive impact in human cancers. The development of therapeutic immunity strategies targeting TADC is promising to enhance their immune-stimulatory capacity in cancers and improve the efficacy of current immunotherapies including immune checkpoint inhibitor (ICI) blockade and DC-based therapies.

Arsenic trioxide induces regulatory functions of plasmacytoid dendritic cells through interferon- inhibition

Arsenic trioxide (As₂O₃) is recently found to have therapeutic potential in systemic sclerosis (SSc), a life-threatening multi-system fibrosing autoimmune disease with type I interferon (IFN-I) signature. Chronically activated plasmacytoid dendritic cells (pDCs) are responsible for IFN-I secretion and are closely related with fibrosis establishment in SSc. In this study, we showed that high concentrations of As₂O₃ induced apoptosis of pDCs via mitochondrial pathway with increased BAX/BCL-2 ratio, while independent of reactive oxygen species generation. Notably, at clinical relevant concentrations, As₂O₃ preferentially inhibited IFN-α secretion as compared to other cytokines such as TNF-α, probably due to potent down-regulation of the total protein and mRNA expression, as well as phosphorylation of the interferon regulatory factor 7 (IRF7). In addition, As₂O₃ induced a suppressive phenotype, and in combination with cytokine inhibition, it down-regulated pDCs’ capacity to induce CD4⁺ T cell proliferation, Th1/Th22 polarization, and B cell differentiation towards plasmablasts. Moreover, chronically activated pDCs from SSc patients were not resistant to the selective IFN-α inhibition, and regulatory phenotype induced by As₂O₃. Collectively, our data suggest that As₂O₃ could target pDCs and exert its treatment efficacy in SSc, and more autoimmune disorders with IFN-I signature.

Single-Cell RNA-Seq Analysis Uncovers Distinct Functional Human NKT Cell Sub-Populations in Peripheral Blood

Vα24-invariant human natural killer T (NKT) cells comprise a unique subset of CD1d-restricted T cells with potent immune regulatory function and are involved in the development of a variety of human diseases. However, the lack of comprehensive molecular subset identities limits their objective classification and clinical application. Using unbiased single-cell RNA sequencing (scRNA-seq) of over 4000 unstimulated and 7000 stimulated human peripheral blood NKT cells, we identified four and five clusters of NKT cells from each NKT group, respectively. Our study uncovers multiple previously unrecognized NKT subsets with potential functional specificities, including a cluster of NKT cells with regulatory T cell property. Flow cytometry and Ingenuity Pathway Analysis confirmed the existence of these NKT populations and indicated the related functional capacities. Our study provides the unbiased and more comprehensive molecular identities of human NKT subsets, which will eventually lead the way to tailored therapies targeting selected NKT subsets.

Human Plasmacytoid Dendritic Cells and Cutaneous Melanoma

The prognosis of metastatic melanoma (MM) patients has remained poor for a long time. However, the recent introduction of effective target therapies (BRAF and MEK inhibitors for BRAFV600-mutated MM) and immunotherapies (anti-CTLA-4 and anti-PD-1) has significantly improved the survival of MM patients. Notably, all these responses are highly dependent on the fitness of the host immune system, including the innate compartment. Among immune cells involved in cancer immunity, properly activated plasmacytoid dendritic cells (pDCs) exert an important role, bridging the innate and adaptive immune responses and directly eliminating cancer cells. A distinctive feature of pDCs is the production of high amount of type I Interferon (I-IFN), through the Toll-like receptor (TLR) 7 and 9 signaling pathway activation. However, published data indicate that melanoma-associated escape mechanisms are in place to hijack pDC functions. We have recently reported that pDC recruitment is recurrent in the early phases of melanoma, but the entire pDC compartment collapses over melanoma progression. Here, we summarize recent advances on pDC biology and function within the context of melanoma immunity.

Immunomodulatory Bonds of the Partnership between Dendritic Cells and T Cells

By acquiring, processing, and presenting both foreign and self-antigens, dendritic cells (DCs) initiate T cell activation that is shaped through the immunomodulatory functions of a variety of cell-membrane-bound molecules including BTLA-HVEM, CD40-CD40L, CTLA-4-CD80/CD86, CD70-CD27, ICOS-ICOS-L, OX40-OX40L, and PD-L1-PD-1, as well as several key cytokines and enzymes such as interleukin-6 (IL-6), IL-12, IL-23, IL-27, transforming growth factor-beta 1 (TGF-β1), retinaldehyde dehydrogenase (Raldh), and indoleamine 2,3-dioxygenase (IDO). Some of these distinct immunomodulatory signals are mediated by specific subsets of DCs, therefore contributing to the functional specialization of DCs in the priming and regulation of immune responses. In addition to responding to the DC-mediated signals, T cells can reciprocally modulate the immunomodulatory capacities of DCs, further refining immune responses. Here, we review recent studies, particularly in experimental mouse systems, that have delineated the integrated mechanisms of crucial immunomodulatory pathways that enable specific populations of DCs and T cells to work intimately together as single functional units that are indispensable for the maintenance of immune homeostasis.

Humanized Mouse Model to Study Type 1 Diabetes

Key requirements in type 1 diabetes (T1D) are in setting up new assays as diagnostic biomarkers that will apply to prediabetes, likely T-cell assays, and in designing antigen-specific therapies to prevent T1D development. New preclinical models of T1D will be required to help with advancing both aims. By crossing mouse strains that lack either murine MHC class I and class II genes and insulin genes, we developed YES mice that instead express human HLA-A*02:01, HLA-DQ8, and insulin genes as transgenes. The metabolic and immune phenotype of YES mice is basically identical to that of the parental strains. YES mice remain insulitis and diabetes free up to 1 year of follow-up, maintain normoglycemia to an intraperitoneal glucose challenge in the long-term range, have a normal β-cell mass, and show normal immune responses to conventional antigens. This new model has been designed to evaluate adaptive immune responses to human insulin on a genetic background that recapitulates a human high-susceptibility HLA-DQ8 genetic background. Although insulitis free, YES mice develop T1D when challenged with polyinosinic-polycytidylic acid. They allow the characterization of preproinsulin epitopes recognized by CD8⁺ and CD4⁺ T cells upon immunization against human preproinsulin or during diabetes development.

Tissue-Specific Roles of NKT Cells in Tumor Immunity

NKT cells are an unusual population of T cells recognizing lipids presented by CD1d, a non-classical class-I-like molecule, rather than peptides presented by conventional MHC molecules. Type I NKT cells use a semi-invariant T cell receptor and almost all recognize a common prototype lipid, α-galactosylceramide (α-GalCer). Type II NKT cells are any lipid-specific CD1d-restricted T cells that use other receptors and generally don't recognize α-GalCer. They play important regulatory roles in immunity, including tumor immunity. In contrast to type I NKT cells that most have found to promote antitumor immunity, type II NKT cells suppress tumor immunity and the two subsets cross-regulate each other, forming an immunoregulatory axis. They also can promote other regulatory cells including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), and can induce MDSCs to secrete TGF-β, one of the most immunosuppressive cytokines known. In some tumors, both Tregs and type II NKT cells can suppress immunosurveillance, and the balance between these is determined by a type I NKT cell. We have also seen that regulation of tumor immunity can depend on the tissue microenvironment, so the same tumor in the same animal in different tissues may be regulated by different cells, such as type II NKT cells in the lung vs Tregs in the skin. Also, the effector T cells that protect those sites when Tregs are removed do not always act between tissues even in the same animal. Thus, metastases may require different immunotherapy from primary tumors. Newly improved sulfatide-CD1d tetramers are starting to allow better characterization of the elusive type II NKT cells to better understand their function and control it to overcome immunosuppression.

Interferon alpha: The key trigger of type 1 diabetes

IFNα is a cytokine essential to a vast array of immunologic processes. Its induction early in the innate immune response provides a priming mechanism that orchestrates numerous subsequent pathways in innate and adaptive immunity. Despite its beneficial effects in viral infections IFNα has been reported to be associated with several autoimmune diseases including autoimmune thyroid disease, systemic lupus erythematosus, rheumatoid arthritis, primary biliary cholangitis, and recently emerged as a major cytokine that triggers Type 1 Diabetes. In this review, we dissect the role of IFNα in T1D, focusing on the potential pathophysiological mechanisms involved. Evidence from human and mouse studies indicates that IFNα plays a key role in enhancing islet expression of HLA-I in patients with T1D, thereby increasing autoantigen presentation and beta cell activation of autoreactive cytotoxic CD8 T-lymphocytes. The binding of IFNα to its receptor induces the secretion of chemokines, attracting monocytes, T lymphocytes, and NK cells to the infected tissue triggering autoimmunity in susceptible individuals. Furthermore, IFNα impairs insulin production through the induction of endoplasmic reticulum stress as well as by impairing mitochondrial function. Due to its central role in the early phases of beta cell death, targeting IFNα and its pathways in genetically predisposed individuals may represent a potential novel therapeutic strategy in the very early stages of T1D.

Plasmacytoid dendritic cell in immunity and cancer

Plasmacytoid dendritic cells (pDCs) comprise a subset of dendritic cells characterized by their ability to produce large amount of type I interferon (IFN-I/α). Originally recognized for their role in modulating immune responses to viral stimulation, growing interest has been directed toward their contribution to tumorigenesis. Under normal conditions, Toll-like receptor (TLR)-activated pDCs exhibit robust IFN-α production and promote both innate and adaptive immune responses. In cancer, however, pDCs demonstrate an impaired response to TLR7/9 activation, decreased or absent IFN-α production and contribute to the establishment of an immunosuppressive tumor microenvironment. In addition to IFN-α production, pDCs can also act as antigen presenting cells (APCs) and regulate immune responses to various antigens. The significant role played by pDCs in regulating both the innate and adaptive components of the immune system makes them a critical player in cancer immunology. In this review, we discuss the development and function of pDCs as well as their role in innate and adaptive immunity. Finally, we summarize pDC contribution to cancer pathogenesis, with a special focus on primary malignant brain tumor, their significance in the era of immunotherapy and suggest potential strategies for pDC-targeted therapy.

Disease-Associated Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs), also called natural interferon (IFN)-producing cells, represent a specialized cell type within the innate immune system. pDCs are specialized in sensing viral RNA and DNA by toll-like receptor-7 and -9 and have the ability to rapidly produce massive amounts of type 1 IFNs upon viral encounter. After producing type 1 IFNs, pDCs differentiate into professional antigen-presenting cells, which are capable of stimulating T cells of the adaptive immune system. Chronic activation of human pDCs by self-DNA or mitochondrial DNA contributes to the pathogenesis of systemic lupus erythematosis and IFN-related autoimmune diseases. Under steady-state conditions, pDCs play an important role in immune tolerance. In many types of human cancers, recruitment of pDCs to the tumor microenvironment contributes to the induction of immune tolerance. Here, we provide a systemic review of recent progress in studies on the role of pDCs in human diseases, including cancers and autoimmune/inflammatory diseases.

Cytotoxic and regulatory roles of mucosal-associated invariant T cells in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease that results from the destruction of pancreatic β-cells by the immune system that involves innate and adaptive immune cells. Mucosal-associated invariant T cells (MAIT cells) are innate-like T-cells that recognize derivatives of precursors of bacterial riboflavin presented by the major histocompatibility complex (MHC) class I-related molecule MR1. Since T1D is associated with modification of the gut microbiota, we investigated MAIT cells in this pathology. In patients with T1D and mice of the non-obese diabetic (NOD) strain, we detected alterations in MAIT cells, including increased production of granzyme B, which occurred before the onset of diabetes. Analysis of NOD mice that were deficient in MR1, and therefore lacked MAIT cells, revealed a loss of gut integrity and increased anti-islet responses associated with exacerbated diabetes. Together our data highlight the role of MAIT cells in the maintenance of gut integrity and the control of anti-islet autoimmune responses. Monitoring of MAIT cells might represent a new biomarker of T1D, while manipulation of these cells might open new therapeutic strategies.

Type 1 diabetes and viral infections: What is the relationship?

Type 1 diabetes (T1D) is the most common chronic metabolic disorder in children. Epigenetic and environmental factors capable of altering the penetrance of major susceptibility genes or capable of increasing the penetrance of low-risk genes are currently thought to play a role in triggering autoimmunity and T1D development. This paper discusses the current knowledge of the role of viruses in T1D. Most studies that have evaluated the potential association between viral infections and T1D have indicated that it is highly likely that some of these infectious agents play a role in T1D development. However, most T1D cases are immune-mediated, and it is supposed that the initial viral infection is capable of creating, in genetically predisposed subjects, a particular condition in which chronic local inflammation occurs through the persistence of the infecting virus in pancreatic tissue and the activation of autoimmunity by means of molecular mimicry, bystander activation, or both. Theoretically, this knowledge could lead to possible prophylaxis and therapy for T1D. Further studies devoted to evaluating which infectious agents are linked to T1D and which immune mechanisms induce or protect against the disease are needed before adequate prophylactic and therapeutic measures can be developed.

The Clonal Invariant NKT Cell Repertoire in People with Type 1 Diabetes Is Characterized by a Loss of Clones Expressing High-Affinity TCRs

Invariant NKT (iNKT) cells in healthy people express iNKT-TCRs with widely varying affinities for CD1d, suggesting different roles for high- and low-affinity iNKT clones in immune regulation. However, the functional implications of this heterogeneity have not yet been determined. Functionally aberrant iNKT responses have been previously demonstrated in different autoimmune diseases, including human type 1 diabetes, but their relationship to changes in the iNKT clonal repertoire have not been addressed. In this study, we directly compared the clonal iNKT repertoire of people with recent onset type 1 diabetes and age- and gender-matched healthy controls with regard to iNKT-TCR affinity and cytokine production. Our results demonstrate a selective loss of clones expressing high-affinity iNKT-TCRs from the iNKT repertoire of people with type 1 diabetes. Furthermore, this bias in the clonal iNKT repertoire in type 1 diabetes was associated with increased GM-CSF, IL-4, and IL-13 cytokine secretion among Ag-stimulated low-affinity iNKT clones. Thus, qualitative changes of the clonal iNKT repertoire with the potential to affect the regulatory function of this highly conserved T cell population are already established at the early stages in type 1 diabetes. These findings may inform future rationales for the development of iNKT-based therapies aiming to restore immune tolerance in type 1 diabetes.

Regulatory role of natural killer T cells in diabetes

Type 1 and type 2 diabetes are growing public health problems. Despite having different pathophysiologies, both diseases are associated with defects in immune regulation. Invariant natural killer T (iNKT) cells are innate-like T cells that recognize glycolipids presented by CD1d. These cells not only play a key role in the defense against pathogens, but also exert potent immunoregulatory functions. The regulatory role of iNKT cells in the prevention of type 1 diabetes has been demonstrated in murine models and analyzed in diabetic patients. The decreased frequency of iNKT cells in non-obese diabetic mice initially suggested the regulatory role of this cell subset. Increasing the frequency or the activation of iNKT cells with agonists protects non-obese diabetic mice from the development of diabetes. Several mechanisms mediate iNKT regulatory functions. They can rapidly produce immunoregulatory cytokines, interleukin (IL)-4 and IL-10. They induce tolerogenic dendritic cells, thereby inducing the anergy of autoreactive anti-islet T cells and increasing the frequency of T regulatory cells (Treg cells). Synthetic agonists are able to activate iNKT cells and represent potential therapeutic treatment in order to prevent type 1 diabetes. Growing evidence points to a role of immune system in glucose intolerance and type 2 diabetes. iNKT cells are resident cells of adipose tissue and their local and systemic frequencies are reduced in obese patients, suggesting their involvement in local and systemic inflammation during obesity. With the discovery of potential continuity between type 1 and type 2 diabetes in some patients, the role of iNKT cells in these diseases deserves further investigation.

Autoimmune Diabetes: An Overview of Experimental Models and Novel Therapeutics

Type 1 diabetes (T1D) results from a chronic and selective destruction of insulin-secreting β-cells within the islets of Langerhans of the pancreas by autoreactive CD4(+) and CD8(+) T lymphocytes. The use of animal models of T1D was instrumental for deciphering the steps of the autoimmune process leading to T1D. The non-obese diabetic (NOD) mouse and the bio-breeding (BB) rat spontaneously develop the disease similar to the human pathology in terms of the immune responses triggering autoimmune diabetes and of the genetic and environmental factors influencing disease susceptibility. The generation of genetically modified models allowed refining our understanding of the etiology and the pathogenesis of the disease. In the present review, we provide an overview of the experimental models generated and used to gain knowledge on the molecular and cellular mechanisms underlying the breakdown of self-tolerance in T1D and the progression of the autoimmune response. Immunotherapeutic interventions designed in these animal models and translated into the clinical arena in T1D patients will also be discussed.

E2-2 Dependent Plasmacytoid Dendritic Cells Control Autoimmune Diabetes

Autoimmune diabetes is a consequence of immune-cell infiltration and destruction of pancreatic β-cells in the islets of Langerhans. We analyzed the cellular composition of the insulitic lesions in the autoimmune-prone non-obese diabetic (NOD) mouse and observed a peak in recruitment of plasmacytoid dendritic cells (pDCs) to NOD islets around 8–9 weeks of age. This peak coincides with increased spontaneous expression of type-1-IFN response genes and CpG₁₅₈₅ induced production of IFN-α from NOD islets. The transcription factor E2-2 is specifically required for the maturation of pDCs, and we show that knocking out E2-2 conditionally in CD11c⁺ cells leads to a reduced recruitment of pDCs to pancreatic islets and reduced CpG₁₅₈₅ induced production of IFN-α during insulitis. As a consequence, insulitis has a less aggressive expression profile of the Th1 cytokine IFN-γ and a markedly reduced diabetes incidence. Collectively, these observations demonstrate a disease-promoting role of E2-2 dependent pDCs in the pancreas during autoimmune diabetes in the NOD mouse.

The multifaceted biology of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are a unique DC subset that specializes in the production of type I interferons (IFNs). pDCs promote antiviral immune responses and have been implicated in the pathogenesis of autoimmune diseases that are characterized by a type I IFN signature. However, pDCs can also induce tolerogenic immune responses. In this Review, we summarize recent progress in the field of pDC biology, focusing on the molecular mechanisms that regulate the development and functions of pDCs, the pathways involved in their sensing of pathogens and endogenous nucleic acids, their functions at mucosal sites, and their roles in infection, autoimmunity and cancer.

iNKT and MAIT Cell Alterations in Diabetes

Type 1 diabetes (T1D) and type 2 diabetes (T2D) are multifactorial diseases with different etiologies in which chronic inflammation takes place. Defects in invariant natural killer T (iNKT) cell populations have been reported in both T1D and T2D patients, mouse models and our recent study revealed mucosal-associated invariant T (MAIT) cell defects in T2D and obese patients. Regarding iNKT cells many studies in non-obese diabetic mice demonstrated their protective role against T1D whereas their potential role in human T1D is still under debate. Studies in mouse models and patients suggest that iNKT cells present in adipose tissue (AT) could exert a regulatory role against obesity and associated metabolic disorders, such as T2D. Scarce data are yet available on MAIT cells; however, we recently described MAIT cell abnormalities in the blood and ATs from obese and T2D patients. These data show that a link between MAIT cells and metabolic disorders pave the way for further investigations on MAIT cells in T1D and T2D in humans and mouse models. Furthermore, we hypothesize that the gut microbiota alterations associated with T1D and T2D could modulate iNKT and MAIT cell frequency and functions. The potential role of iNKT and MAIT cells in the regulation of metabolic pathways and their cross-talk with microbiota represent exciting new lines of research.

The Role of Dendritic Cell Subsets and Innate Immunity in the Pathogenesis of Type 1 Diabetes and Other Autoimmune Diseases

Dendritic cells (DCs) are key antigen-presenting cells that have an important role in autoimmune pathogenesis. DCs control both steady-state T cell tolerance and activation of pathogenic responses. The balance between these two outcomes depends on several factors, including genetic susceptibility, environmental signals that stimulate varied innate responses, and which DC subset is presenting antigen. Although the specific DC phenotype can diverge depending on the tissue location and context, there are four main subsets identified in both mouse and human: conventional cDC1 and cDC2, plasmacytoid DCs, and monocyte-derived DCs. In this review, we will discuss the role of these subsets in autoimmune pathogenesis and regulation, as well as the genetic and environmental signals that influence their function. Specific topics to be addressed include impact of susceptibility loci on DC subsets, alterations in DC subset development, the role of infection- and host-derived innate inflammatory signals, and the role of the intestinal microbiota on DC phenotype. The effects of these various signals on disease progression and the relative effects of DC subset composition and maturation level of DCs will be examined. These areas will be explored using examples from several autoimmune diseases but will focus mainly on type 1 diabetes.

Regulatory Role of Natural Killer T Cells in Diabetes

Type 1 and type 2 diabetes are growing public health problems. Despite having different pathophysiologies, both diseases are associated with defects in immune regulation. Invariant natural killer T (iNKT) cells are innate-like T cells that recognize glycolipids presented by CD1d. These cells not only play a key role in the defense against pathogens, but also exert potent immunoregulatory functions. The regulatory role of iNKT cells in the prevention of type 1 diabetes has been demonstrated in murine models and analyzed in diabetic patients. The decreased frequency of iNKT cells in non-obese diabetic mice initially suggested the regulatory role of this cell subset. Increasing the frequency or the activation of iNKT cells with agonists protects non-obese diabetic mice from the development of diabetes. Several mechanisms mediate iNKT regulatory functions. They can rapidly produce immunoregulatory cytokines, interleukin (IL)-4 and IL-10. They induce tolerogenic dendritic cells, thereby inducing the anergy of autoreactive anti-islet T cells and increasing the frequency of T regulatory cells (Treg cells). Synthetic agonists are able to activate iNKT cells and represent potential therapeutic treatment in order to prevent type 1 diabetes. Growing evidence points to a role of immune system in glucose intolerance and type 2 diabetes. iNKT cells are resident cells of adipose tissue and their local and systemic frequencies are reduced in obese patients, suggesting their involvement in local and systemic inflammation during obesity. With the discovery of potential continuity between type 1 and type 2 diabetes in some patients, the role of iNKT cells in these diseases deserves further investigation.

Cellular mechanisms of CCL22-mediated attenuation of autoimmune diabetes

Autoimmune destruction of insulin-producing β cells in type 1 diabetes and islet transplantation involves a variety of immune pathways but is primarily mediated by self-reactive T cells. Chemokines can modulate local immune responses in inflammation and tumors by recruiting immune cells. We have reported that expression of the chemokine CCL22 in pancreatic β cells in the NOD mouse prevents autoimmune attack by recruiting T regulatory cells (Tregs), protecting mice from diabetes. In this study we show that invariant NKT cells are also recruited to CCL22-expressing islet transplants and are required for CCL22-mediated protection from autoimmunity. Moreover, CCL22 induces an influx of plasmacytoid dendritic cells, which correlates with higher levels of IDO in CCL22-expressing islet grafts. In addition to its chemotactic properties, we found that CCL22 activates Tregs and promotes their ability to induce expression of IDO by dendritic cells. Islet CCL22 expression thus produces a tolerogenic milieu through the interplay of Tregs, invariant NKT cells, and plasmacytoid dendritic cells, which results in suppression of effector T cell responses and protection of β cells. The immunomodulatory properties of CCL22 could be harnessed for prevention of graft rejection and type 1 diabetes as well as other autoimmune disorders.

Enteroviruses, hygiene and type 1 diabetes: toward a preventive vaccine

Enteroviruses and humans have long co-existed. Although recognized in ancient times, poliomyelitis and type 1 diabetes (T1D) were exceptionally rare and not epidemic, due in large part to poor sanitation and personal hygiene which resulted in repeated exposure to fecal-oral transmitted viruses and other infectious agents and viruses and the generation of a broad protective immunity. As a function of a growing acceptance of the benefits of hygienic practices and microbiologically clean(er) water supplies, the likelihood of exposure to diverse infectious agents and viruses declined. The effort to vaccinate against poliomyelitis demonstrated that enteroviral diseases are preventable by vaccination and led to understanding how to successfully attenuate enteroviruses. Type 1 diabetes onset has been convincingly linked to infection by numerous enteroviruses including the group B coxsackieviruses (CVB), while studies of CVB infections in NOD mice have demonstrated not only a clear link between disease onset but an ability to reduce the incidence of T1D as well: CVB infections can suppress naturally occurring autoimmune T1D. We propose here that if we can harness and develop the capacity to use attenuated enteroviral strains to induce regulatory T cell populations in the host through vaccination, then a vaccine could be considered that should function to protect against both autoimmune as well as virus-triggered T1D. Such a vaccine would not only specifically protect from certain enterovirus types but more importantly, also reset the organism's regulatory rheostat making the further development of pathogenic autoimmunity less likely.

Advances in the cellular immunological pathogenesis of type 1 diabetes

Type 1 diabetes is an autoimmune disease caused by the immune-mediated destruction of insulin-producing pancreatic β cells. In recent years, the incidence of type 1 diabetes continues to increase. It is supposed that genetic, environmental and immune factors participate in the damage of pancreatic β cells. Both the immune regulation and the immune response are involved in the pathogenesis of type 1 diabetes, in which cellular immunity plays a significant role. For the infiltration of CD4(+) and CD8(+) T lymphocyte, B lymphocytes, natural killer cells, dendritic cells and other immune cells take part in the damage of pancreatic β cells, which ultimately lead to type 1 diabetes. This review outlines the cellular immunological mechanism of type 1 diabetes, with a particular emphasis to T lymphocyte and natural killer cells, and provides the effective immune therapy in T1D, which is approached at three stages. However, future studies will be directed at searching for an effective, safe and long-lasting strategy to enhance the regulation of a diabetogenic immune system with limited toxicity and without global immunosuppression.

Plasmacytoid dendritic cells license regulatory T cells, upon iNKT-cell stimulation, to prevent autoimmune diabetes

Invariant NKT (iNKT)-cell stimulation with exogenous specific ligands prevents the development of type 1 diabetes (T1D) in NOD mice. Studies based on anti-islet T-cell transfer showed that iNKT cells prevent the differentiation of these T cells into effector T cells in the pancreatic lymph nodes (PLNs). We hypothesize that this defective priming could be explained by the ability of iNKT cells to induce tolerogenic dendritic cells (DCs) in the PLNs. We evaluated the effect of iNKT-cell stimulation on T1D development by transferring naïve diabetogenic BDC2.5 T cells into proinsulin 2(-/-) NOD mice treated with a long-lasting α-galactosylceramide regimen. In this context, iNKT cells induce the conversion of BDC2.5 T cells into Foxp3(+) Treg cells in the PLNs accumulating in the pancreatic islets. Furthermore, tolerogenic plasmacytoid DCs (pDCs) characterized by low MHC class II molecule expression and TGF-β production are critical in the PLNs for the recruitment of Treg cells into the pancreatic islets by inducing CXCR3 expression. Accordingly, pDC depletion in α-galactosylceramide-treated proinsulin 2(-/-) NOD mice abrogates the protection against T1D. These findings reveal that upon repetitive iNKT-cell stimulation, pDCs are critical for the recruitment of Treg cells in the pancreatic islets and the prevention of T1D development.

Biology of CD1- and MR1-restricted T cells

Over the past 15 years, investigators have shown that T lymphocytes can recognize not only peptides in the context of MHC class I and class II molecules but also foreign and self-lipids in association with the nonclassical MHC class I-like molecules, CD1 proteins. In this review, we describe the most recent events in the field, with particular emphasis on (a) structural and functional aspects of lipid presentation by CD1 molecules, (b) the development of CD1d-restricted invariant natural killer T (iNKT) cells and transcription factors required for their differentiation, (c) the ability of iNKT cells to modulate innate and adaptive immune responses through their cross talk with lymphoid and myeloid cells, and (d) MR1-restricted and group I (CD1a, CD1b, and CD1c)-restricted T cells.

The immunoregulatory role of type I and type II NKT cells in cancer and other diseases

NKT cells are CD1d-restricted T cells that recognize lipid antigens. They also have been shown to play critical roles in the regulation of immune responses. In the immune responses against tumors, two subsets of NKT cells, type I and type II, play opposing roles and cross-regulate each other. As members of both the innate and adaptive immune systems, which form a network of multiple components, they also interact with other immune components. Here, we discuss the function of NKT cells in tumor immunity and their interaction with other regulatory cells, especially CD4(+)CD25(+)Foxp3(+) regulatory T cells.

Dendritic cell subsets in type 1 diabetes: friend or foe?

Type 1 diabetes (T1D) is a T cell mediated autoimmune disease characterized by immune mediated destruction of the insulin-producing β cells in the islets of Langerhans. Dendritic cells (DC) have been implicated in the pathogenesis of T1D and are also used as immunotherapeutic agents. Plasmacytoid (p)DC have been shown to have both protective and pathogenic effects and a newly described merocytic DC population has been shown to break tolerance in the mouse model of T1D, the non-obese diabetic (NOD) mouse. We have used DC populations to prevent the onset of T1D in NOD mice and clinical trials of DC therapy in T1D diabetes have been initiated. In this review we will critically examine the recent published literature on the role of DC subsets in the induction and regulation of the autoimmune response in T1D.

Protection against type 1 diabetes upon Coxsackievirus B4 infection and iNKT-cell stimulation: role of suppressive macrophages

Invariant natural killer T (iNKT) cells belong to the innate immune system and exercise a dual role as potent regulators of autoimmunity and participate in responses against different pathogens. They have been shown to prevent type 1 diabetes development and to promote antiviral responses. Many studies in the implication of environmental factors on the etiology of type 1 diabetes have suggested a link between enteroviral infections and the development of this disease. This study of the pancreatropic enterovirus Coxsackievirus B4 (CVB4) shows that although infection accelerated type 1 diabetes development in a subset of proinsulin 2-deficient NOD mice, the activation of iNKT cells by a specific agonist, α-galactosylceramide, at the time of infection inhibited the disease. Diabetes development was associated with the infiltration of pancreatic islets by inflammatory macrophages, producing high levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α and activation of anti-islet T cells. On the contrary, macrophages infiltrating the islets after CVB4 infection and iNKT-cell stimulation expressed a number of suppressive enzymes, among which indoleamine 2,3-dioxygenase was sufficient to inhibit anti-islet T-cell response and to prevent diabetes. This study highlights the critical interaction between virus and the immune system in the acceleration or prevention of type 1 diabetes.

[Regulatory role of NKT cells in the prevention of type 1 diabetes]

Type 1 diabetes is an autoimmune disease resulting from the destruction of pancreatic β cells by the immune system. NKT cells are innate-like T cells that can exert potent immuno-regulatory functions. The regulatory role of NKT cells was initially proposed after the observed decreased frequency of this subset in mouse models of type 1 diabetes, as well as in patients developing various autoimmune pathologies. Increasing NKT cell frequency and function prevent the development of type 1 diabetes in mouse models. Several mechanisms including IL-4 and IL-10 production by NKT cells and the accumulation of tolerogenic dendritic cells are critical for the dampening of pathogenic anti-islet T cell responses by NKT cells. Importantly, these cells can at the same time prevent diabetes and promote efficient immune responses against infectious agents. These results strengthen the potential role of NKT cells as a key target for the development of therapeutic strategies against type 1 diabetes.

The preventive role of type 2 NKT cells in the development of type 1 diabetes

In the last two decades, natural killer T (NKT) cells have emerged as an important factor in preventing type 1 diabetes (T1D) when investigated in the experimental non-obese diabetic (NOD) mouse model. So far, investigations have largely focused on type 1 NKT cells with invariant T-cell receptors, whereas the role of type 2 NKT cells with diverse T-cell receptors is less well understood. However, there have been several findings which indicate that in fact type 2 NKT cells may regulate the progression of type 1 diabetes in NOD mice, including a fraction of these cells which recognize β-cell-enriched sulfatide. Therefore, the focus for this review is to present the current evidence of the effect of type 2 NKT cells on the development of T1D. In general, there is still uncertainty surrounding the mechanism of activation and function of NKT cells. Here, we present two models of the effector mechanisms, respectively, Th1/Th2 polarization and the induction of tolerogenic dendritic cells (DC). In conclusion, this review points to the importance of immunoregulation by type 2 NKT cells in preventing the development of T1D and highlights the induction of tolerogenic DC as a likely mechanism. The possible therapeutic role of type 1 and type 2 NKT cells are evaluated and future experiments concerning type 2 NKT cells and T1D are proposed.

Secretory IgA induces tolerogenic dendritic cells through SIGNR1 dampening autoimmunity in mice

IgA plays ambivalent roles in the immune system. The balance between inhibitory and activating responses relies on the multimerization status of IgA and interaction with their cognate receptors. In mucosal sites, secretory IgA (SIgA) protects the host through immune-exclusion mechanisms, but its function in the bloodstream remains unknown. Using bone marrow-derived dendritic cells, we found that both human and mouse SIgA induce tolerogenic dendritic cells (DCs) following binding to specific ICAM-3 grabbing nonintegrin receptor 1. This interaction was dependent on Ca(2+) and mannose residues. SIgA-primed DCs (SIgA-DCs) are resistant to TLR-dependent maturation. Although SIgA-DCs fail to induce efficient proliferation and Th1 differentiation of naive responder T cells, they generate the expansion of regulatory T cells through IL-10 production. SIgA-DCs are highly potent in inhibiting autoimmune responses in mouse models of type 1 diabetes and multiple sclerosis. This discovery may offer new insights about mucosal-derived DC immunoregulation through SIgA opening new therapeutic approaches to autoimmune diseases.

The case for virus-induced type 1 diabetes

PURPOSE OF REVIEW

Type 1 diabetes (T1D) results from the immune-mediated destruction of pancreatic insulin-producing cells because of the interaction among genetic susceptibility, the immune system and environmental factor(s). A possible role of viral infections in T1D pathogenesis has been hypothesized for some time; however, only in the most recent years, studies performed at the molecular and cellular level are starting to shed light on this issue.

RECENT FINDINGS

Studies in animal models and in man have shown that viruses can indeed infect pancreatic beta-cells, inducing islet inflammation and functional damage. In addition, recent in-situ investigations performed on pancreatic tissue samples have provided evidence that in addition to adaptive immune response, innate immunity is involved in T1D pathogenesis and the whole pancreas (not only its endocrine portion) is infiltrated by immune-mediated phenomena.

SUMMARY

The established role of inflammation in the insulitic process and the increasing evidence in support of the contribution of viral infections to a proinflammatory islet scenario are strongly suggestive that viruses may indeed contribute to beta-cell damage and dysfunction, thus setting the stage for the design of antiviral strategies (e.g. vaccines and antiviral drugs) aimed at protecting the beta-cells.

Bacterial CD1d-restricted glycolipids induce IL-10 production by human regulatory T cells upon cross-talk with invariant NKT cells

Invariant NKT (iNKT) cells and CD4(+)CD25(+)FOXP3(+) regulatory T cells (Tregs) are important immune regulatory T cells with Ag reactivity to glycolipids and peptides, respectively. However, the functional interplay between these cells in humans is poorly understood. We show that Tregs suppress iNKT cell proliferation induced by CD1d-restricted glycolipids, including bacterial-derived diacylglycerols, as well as by innate-like activation. Inhibition was related to the potency of iNKT agonists, making diacylglycerol iNKT responses very prone to suppression. Cytokine production by iNKT cells was differentially modulated by Tregs because IL-4 production was reduced more profoundly compared with IFN-γ. A compelling observation was the significant production of IL-10 by Tregs after cell contact with iNKT cells, in particular in the presence of bacterial diacylglycerols. These iNKT-primed Tregs showed increased FOXP3 expression and superior suppressive function. Suppression of iNKT cell responses, but not conventional T cell responses, was IL-10 dependent, suggesting that there is a clear difference in mechanism between the Treg-mediated inhibition of these cell types. Our data highlight a physiologically relevant interaction between human iNKT and Tregs upon pathogen-derived glycolipid recognition that has a significant impact on the design of iNKT cell-based therapeutics.

Dendritic cell subtypes from lymph nodes and blood show contrasted gene expression programs upon Bluetongue virus infection

Human and animal hemorrhagic viruses initially target dendritic cells (DCs). It has been proposed, but not documented, that both plasmacytoid DCs (pDCs) and conventional DCs (cDCs) may participate in the cytokine storm encountered in these infections. In order to evaluate the contribution of DCs in hemorrhagic virus pathogenesis, we performed a genome-wide expression analysis during infection by Bluetongue virus (BTV), a double-stranded RNA virus that induces hemorrhagic fever in sheep and initially infects cDCs. Both pDCs and cDCs accumulated in regional lymph nodes and spleen during BTV infection. The gene response profiles were performed at the onset of the disease and markedly differed with the DC subtypes and their lymphoid organ location. An integrative knowledge-based analysis revealed that blood pDCs displayed a gene signature related to activation of systemic inflammation and permeability of vasculature. In contrast, the gene profile of pDCs and cDCs in lymph nodes was oriented to inhibition of inflammation, whereas spleen cDCs did not show a clear functional orientation. These analyses indicate that tissue location and DC subtype affect the functional gene expression program induced by BTV and suggest the involvement of blood pDCs in the inflammation and plasma leakage/hemorrhage during BTV infection in the real natural host of the virus. These findings open the avenue to target DCs for therapeutic interventions in viral hemorrhagic diseases.

Viruses and type 1 diabetes: a new look at an old story

Epidemiological data suggesting an infectious origin of diabetes pre-date the discovery of insulin; indeed it was the variation in mortality rates from diabetes that led Gunderson to hypothesise that a virus with 'selective affinity for the pancreas' may cause 'acute diabetes' in youth (1). He noted an increase in deaths from diabetes in young people aged 10-20 yr in Norway from 1900 to 1921 following epidemics of parotitis, with a lag time of 3-4 yr between infection and death. In Norway, Denmark,France, and America, the increase in deaths from diabetes exceeded the expected number based on population growth; lending further weight to the proposal that diabetes was caused by infection. Since that time,a large body of epidemiological, clinical and experimental research, in humans, cellular and animal models, has provided further insights into the contribution of infections in the development of type 1 diabetes.Epidemiological evidence for a viral aetiology of diabetes A substantial body of epidemiological data point to a significant contribution of the environment in the development of type 1 diabetes,although much of the evidence is not specific to viruses per se. These data include rising rates of type 1 diabetes in both developed and developing countries in recent decades (2, 3) and a reduced contribution of high risk human leucocyte antigen (HLA) genotypes (4, 5), indicating that non-genetic factors are important. Similarly, the pairwise concordance between monozygotic twins for type 1 diabetes of less than 40%, and the observation that the incidence of diabetes in migrant children reflects that of their adopted country (6, 7), provide circumstantial evidence that environmental agents contribute to the disease. Space-time clustering in the presentation of type 1 diabetes (8-10) and clustering of births in children who subsequently develop diabetes (11) support a direct role for infections in the initiation and acceleration of the disease process.