Activation of islet autoreactive naïve T cells in infants is influenced by homeostatic mechanisms and antigen-presenting capacity

Why does the immune system destroy pancreatic β-cells but not α-cells in type 1 diabetes?

A perplexing feature of type 1 diabetes (T1D) is that the immune system destroys pancreatic β-cells but not neighbouring α-cells, even though both β-cells and α-cells are dysfunctional. Dysfunction, however, progresses to death only for β-cells. Recent findings indicate important differences between these two cell types. First, expression of BCL2L1, a key antiapoptotic gene, is higher in α-cells than in β-cells. Second, endoplasmic reticulum (ER) stress-related genes are differentially expressed, with higher expression levels of pro-apoptotic CHOP in β-cells than in α-cells and higher expression levels of HSPA5 (which encodes the protective chaperone BiP) in α-cells than in β-cells. Third, expression of viral recognition and innate immune response genes is higher in α-cells than in β-cells, contributing to the enhanced resistance of α-cells to coxsackievirus infection. Fourth, expression of the immune-inhibitory HLA-E molecule is higher in α-cells than in β-cells. Of note, α-cells are less immunogenic than β-cells, and the CD8+ T cells invading the islets in T1D are reactive to pre-proinsulin but not to glucagon. We suggest that this finding is a result of the enhanced capacity of the α-cell to endure viral infections and ER stress, which enables them to better survive early stressors that can cause cell death and consequently amplify antigen presentation to the immune system. Moreover, the processing of the pre-proglucagon precursor in enteroendocrine cells might favour immune tolerance towards this potential self-antigen compared to pre-proinsulin.

Asymmetric T cell division of GAD65 specific naive T cells contribute to an early divergence in the differentiation fate into memory T cell subsets

Autoreactive T cells with the phenotype and function of different memory subsets are present in patients who developed type 1 diabetes. According to the progressive differentiation model, memory subsets generate from naïve precursors in a linear and unidirectional path depending on the strength and quality of stimulatory signals. By observing human naïve T cells in contact with GAD65 loaded autologous dendritic cells, we observed that approximately 10% of cells divided with the plane of cell division parallel to the one of the immune synapse, causing phenotypic asymmetries in the proximal and distal daughter T cells. After the first T cell division, proximal and distal daughter T cells showed different phenotype, metabolic signature and commitment to differentiate toward long-lived memory T cells or T cells with effector function. Subjects with or without T1D showed a similar frequency of asymmetric T cell division (ATCD) for autoantigens and recall antigens specific T cells, however the frequency of ATCD is significantly increased in autoreactive T cells in patients with T1D when IL-7 was added to the culture. An increased up-regulation of GLUT1 in response to IL-7 in patients with T1D was related to the rate of ATCD Our results showed that ATCD is associated with an early divergence in the differentiation fate of naïve T cells specific for GAD65 during first antigen encounter. This article is protected by copyright. All rights reserved.

InsB9-23 Gene Transfer to Hepatocyte-Based Combined Therapy Abrogates Recurrence of Type 1 Diabetes After Islet Transplantation

The induction of antigen (Ag)-specific tolerance represents a therapeutic option for autoimmune diabetes. We demonstrated that administration of a lentiviral vector enabling expression of insulin B chain 9-23 (InsB9-23) (LV.InsB) in hepatocytes arrests β-cell destruction in prediabetic NOD mice by generating InsB9-23-specific FoxP3⁺ T regulatory cells (Tregs). LV.InsB in combination with a suboptimal dose of anti-CD3 monoclonal antibody (combined therapy [CT], 1 × 5 μg [CT5]) reverts diabetes and prevents recurrence of autoimmunity after islet transplantation in ∼50% of NOD mice. We investigated whether CT optimization could lead to abrogation of recurrence of autoimmunity. Therefore, alloislets were transplanted after optimized CT tolerogenic conditioning (1 × 25 μg [CT25]). Diabetic NOD mice conditioned with CT25 when glycemia was <500 mg/dL remained normoglycemic for 100 days after alloislet transplantation and displayed reduced insulitis, but independently from the graft. Accordingly, cured mice showed T-cell unresponsiveness to InsB9-23 stimulation and increased Treg frequency in islet infiltration and pancreatic lymph nodes. Additional studies revealed a complex mechanism of Ag-specific immune regulation driven by CT25, in which both Tregs and PDL1 costimulation cooperate to control diabetogenic cells, while transplanted islets play a crucial role, although transient, recruiting diabetogenic cells. Therefore, CT25 before alloislet transplantation represents an Ag-specific immunotherapy to resolve autoimmune diabetes in the presence of residual endogenous β-cell mass.

Insulin-Reactive T Cells Convert Diabetogenic Insulin-Reactive VH125 B Cells Into Tolerogenic Cells by Reducing Germinal Center T:B Cell Interactions in NOD Mice

Insulin is a key autoantigen in Type 1 Diabetes (T1D), targeted by both T and B cells. Therefore, understanding insulin-specific T:B cell interactions is important. We have previously reported an insulin-reactive CD4+ T cell, (designated 2H6). Unlike other insulin-reactive T cells, 2H6 cells protect non-obese diabetic (NOD) mice from T1D development, mediated by TGFβ. To investigate insulin-specific T:B cell interactions, we bred 2H6αβ T cell receptor transgenic NOD mice (2H6) with the insulin-reactive B cell receptor transgenic NOD mice (VH125), generating 2H6VH125 NOD mice. Similar to 2H6 mice, 2H6VH125 mice are protected from T1D development. Interestingly, VH125 B cells did not alter the phenotype of 2H6 T cells; however, 2H6 T cells significantly altered the VH125 B cells by reducing the insulin-reactive non-germinal center (GC) and GC B cells, as well as MHC and costimulatory molecule expression on the B cells. Furthermore, the B cells in 2H6VH125 NOD mice exhibited increased non-insulin-specific and a class switched IgG isotype, which can be recapitulated in vivo in Rag-deficient NOD mice by adoptive transfer. In vitro, VH125 B cells from 2H6VH125 mice suppressed the proliferation of 2H6 T cells to insulin antigen but enhanced TGFβ secretion by 2H6 T cells from 2H6VH125 mice compared to 2H6 mice. In summary, our data showed that 2H6 CD4+ T cells alter the phenotype and function of insulin-reactive B cells from pathogenic to tolerogenic cells. In turn, VH125 B cells also modulate the function of the 2H6 T cells. Thus, promoting the interactions between antigen-specific regulatory T cells and B cells may lead to protection from T1D.

Manipulation of Glucose Availability to Boost Cancer Immunotherapies

The orchestration of T cell responses is intimately linked to the execution of metabolic processes, both in homeostasis and disease. In cancer tissues, metabolic alterations that characterize malignant transformation profoundly affect the composition of the immune microenvironment and the accomplishment of an effective anti-tumor response. The growing understanding of the metabolic regulation of immune cell function has shed light on the possibility to manipulate metabolic pathways as a strategy to improve T cell function in cancer. Among others, glucose metabolism through the glycolytic pathway is central in shaping T cell responses and emerges as an ideal target to improve cancer immunotherapy. However, metabolic manipulation requires a deep level of control over side-effects and development of biomarkers of response. Here, we summarize the metabolic control of T cell function and focus on the implications of metabolic manipulation for the design of immunotherapeutic strategies. Integrating our understanding of T cell function and metabolism will hopefully foster the forthcoming development of more effective immunotherapeutic strategies.

Neonatal gut microbiome and immunity

Early life is a critical time window for the neonatal gut to be progressively populated with different bacterial species that collectively promote gut maturation. A fully developed and healthy gut microbiome in neonates is an important driver for the development of other aspects of health. Unlike the relatively stable gut microbiome in adults, the developing gut microbiome in neonates exhibits higher plasticity and adaptability. This also underscores the unique window of opportunity for intervention or preventive measures to improve long-term health through modulations of the gut microbiome in early life. Better understanding of the neonatal gut microbiome - how it arises and how it impacts immune cell development - will help us appreciate the underpinnings of immune-related diseases. Here, we examine recent findings on the neonatal gut microbiome and discuss their implications for understanding this important driver of the maturation of the immune system and immunity against infections in early life.

Maternal Type 1 Diabetes Reduces Autoantigen-Responsive CD4+ T Cells in Offspring

Autoimmunity against pancreatic β-cell autoantigens is a characteristic of childhood type 1 diabetes (T1D). Autoimmunity usually appears in genetically susceptible children with the development of autoantibodies against (pro)insulin in early childhood. The offspring of mothers with T1D are protected from this process. The aim of this study was to determine whether the protection conferred by maternal T1D is associated with improved neonatal tolerance against (pro)insulin. Consistent with improved neonatal tolerance, the offspring of mothers with T1D had reduced cord blood CD4⁺ T-cell responses to proinsulin and insulin, a reduction in the inflammatory profile of their proinsulin-responsive CD4⁺ T cells, and improved regulation of CD4⁺ T cell responses to proinsulin at 9 months of age, as compared with offspring with a father or sibling with T1D. Maternal T1D was also associated with a modest reduction in CpG methylation of the INS gene in cord blood mononuclear cells from offspring with a susceptible INS genotype. Our findings support the concept that a maternal T1D environment improves neonatal immune tolerance against the autoantigen (pro)insulin.

Pharmacological Targeting of GLUT1 to Control Autoreactive T Cell Responses

An increasing body of evidence indicates that bio-energetic metabolism of T cells can be manipulated to control T cell responses. This potentially finds a field of application in the control of the T cell responses in autoimmune diseases, including in type 1 diabetes (T1D). Of the possible metabolic targets, Glut1 gained considerable interest because of its pivotal role in glucose uptake to fuel glycolysis in activated T cells, and the recent development of a novel class of small molecules that act as selective inhibitor of Glut1. We believe we can foresee a possible application of pharmacological Glut1 blockade approach to control autoreactive T cells that destroy insulin producing beta cells. However, Glut1 is expressed in a broad range of cells in the body and off-target and side effect are possible complications. Moreover, the duration of the treatment and the age of patients are critical aspects that need to be addressed to reduce toxicity. In this paper, we will review recent literature to determine whether it is possible to design a pharmacological Glut1 blocking strategy and how to apply this to autoimmunity in T1D.

Inducible IL-7 Hyperexpression Influences Lymphocyte Homeostasis and Function and Increases Allograft Rejection

The IL-7/IL-7R pathway is essential for lymphocyte development and disturbances in the pathway can lead to immune deficiency or T cell mediated destruction. Here, the effect of transient hyperexpression of IL-7 was investigated on immune regulation and allograft rejection under immunosuppression. An experimental in vivo immunosuppressive mouse model of IL-7 hyperexpression was developed using transgenic mice (C57BL/6 background) carrying a tetracycline inducible IL-7 expression cassette, which allowed the temporally controlled induction of IL-7 hyperexpression by Dexamethasone and Doxycycline treatment. Upon induction of IL-7, the B220⁺ c-kit⁺ Pro/Pre-B I compartment in the bone marrow increased as compared to control mice in a serum IL-7 concentration-correlated manner. IL-7 hyperexpression also preferentially increased the population size of memory CD8⁺ T cells in secondary lymphoid organs, and reduced the proportion of CD4⁺Foxp3⁺ T regulatory cells. Of relevance to disease, conventional CD4⁺ T cells from an IL-7-rich milieu escaped T regulatory cell-mediated suppression in vitro and in a model of autoimmune diabetes in vivo. These findings were validated using an IL-7/anti-IL7 complex treatment mouse model to create an IL-7 rich environment. To study the effect of IL-7 on islet graft survival in a mismatched allograft model, BALB/c mice were rendered diabetic by streptozotocin und transplanted with IL-7-inducible or control islets from C57BL/6 mice. As expected, Dexamethasone and Doxycycline treatment prolonged graft median survival as compared to the untreated control group in this transplantation mouse model. However, upon induction of local IL-7 hyperexpression in the transplanted islets, graft survival time was decreased and this was accompanied by an increased CD4⁺ and CD8⁺ T cell infiltration in the islets. Altogether, the findings show that transient elevations of IL-7 can impair immune regulation and lead to graft loss also under immune suppression.

Detection and Characterization of CD8+ Autoreactive Memory Stem T Cells in Patients With Type 1 Diabetes

Stem memory T cells (Tscm) constitute the earliest developmental stage of memory T cells, displaying stem cell-like properties, such as self-renewal capacity. Their superior immune reconstitution potential has sparked interest in cancer immune therapy, vaccine development, and immune reconstitution, whereas their role in autoimmunity is largely unexplored. Here we show that autoreactive CD8⁺ Tscm specific for β-cell antigens GAD65, insulin, and IGRP are present in patients with type 1 diabetes (T1D). In vitro, the generation of autoreactive Tscm from naive precursors required the presence of the homeostatic cytokine interleukin-7 (IL-7). IL-7 promotes glucose uptake via overexpression of GLUT1 and upregulation of the glycolytic enzyme hexokinase 2. Even though metabolism depends on glucose uptake, the subsequent oxidation of pyruvate in the mitochondria was necessary for Tscm generation from naive precursors. In patients with T1D, high expression of GLUT1 was a hallmark of circulating Tscm, and targeting glucose uptake via GLUT1 using the selective inhibitor WZB117 resulted in inhibition of Tscm generation and expansion. Our results suggest that autoreactive Tscm are present in patients with T1D and can be selectively targeted by inhibition of glucose metabolism.

The Neonatal Window of Opportunity: Setting the Stage for Life-Long Host-Microbial Interaction and Immune Homeostasis

The existence of a neonatal window was first highlighted by epidemiological studies that revealed the particular importance of this early time in life for the susceptibility to immune-mediated diseases in humans. Recently, the first animal studies emerged that present examples of early-life exposure-triggered persisting immune events, allowing a detailed analysis of the factors that define this particular time period. The enteric microbiota and the innate and adaptive immune system represent prime candidates that impact on the pathogenesis of immune-mediated diseases and are known to reach a lasting homeostatic equilibrium following a dynamic priming period after birth. In this review, we outline the postnatal establishment of the microbiota and maturation of the innate and adaptive immune system and discuss examples of early-life exposure-triggered immune-mediated diseases that start to shed light on the critical importance of the early postnatal period for life-long immune homeostasis.

T-cell Metabolism as a Target to Control Autoreactive T Cells in β-Cell Autoimmunity

PURPOSE OF REVIEW

An increasing body of evidence indicates that bio-energetic metabolism of activated T cells is a potential target to control the autoimmune response in type 1 diabetes (T1D).

RECENT FINDINGS

T-cell activation and proliferation is linked to the cell capacity to provide sufficient energy and biosynthesis molecules to support T-cell growth and division. This makes T cells susceptible to metabolic inhibition for the control of the T-cell response. There is a wide therapeutic arsenal of metabolic inhibitors, including novel classes of drugs that have become recently available. With the current knowledge and availability of metabolic inhibitors, we are now in the position to design a metabolic inhibition strategy to determine whether targeting of autoreactive T cells is an effective strategy to control the process of β-cell destruction in T1D.

Perinatal tolerance to proinsulin is sufficient to prevent autoimmune diabetes

High-affinity self-reactive thymocytes are purged in the thymus, and residual self-reactive T cells, which are detectable in healthy subjects, are controlled by peripheral tolerance mechanisms. Breakdown in these mechanisms results in autoimmune disease, but antigen-specific therapy to augment natural mechanisms can prevent this. We aimed to determine when antigen-specific therapy is most effective. Islet autoantigens, proinsulin (PI), and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) were expressed in the antigen-presenting cells (APCs) of autoimmune diabetes-prone nonobese diabetic (NOD) mice in a temporally controlled manner. PI expression from gestation until weaning was sufficient to completely protect NOD mice from diabetes, insulitis, and development of insulin autoantibodies. Insulin-specific T cells were significantly diminished, were naive, and did not express IFN-γ when challenged. This long-lasting effect from a brief period of treatment suggests that autoreactive T cells are not produced subsequently. We tracked IGRP_206-214-specific CD8⁺ T cells in NOD mice expressing IGRP in APCs. When IGRP was expressed only until weaning, IGRP_206-214-specific CD8⁺ T cells were not detected later in life. Thus, anti-islet autoimmunity is determined during early life, and autoreactive T cells are not generated in later life. Bolstering tolerance to islet antigens in the perinatal period is sufficient to impart lasting protection from diabetes.

Targeting Homeostatic T Cell Proliferation to Control Beta-Cell Autoimmunity

Immunomodulation of the autoreactive T cell response is considered a major strategy to control beta-cell autoimmunity, both in the natural history of type 1 diabetes and in islet transplantation, which can be affected by autoimmunity recurrence. So far, these strategies have had modest results, prompting efforts to define novel cellular and molecular targets to control autoreactive T cell expansion and activation. Novel findings highlighted the important role of the homeostatic cytokine interleukin-7 in inducing proliferation and differentiation of autoreactive T cell clones that causes beta-cell autoimmunity. In this review, we discuss recent evidences and novel findings on the role of IL-7 mediated homeostatic T cell proliferation in the process of beta-cell destruction and evidences of how targeting IL-7 and its receptor could be an innovative and effective strategy to control beta-cell autoimmunity.

Analysis of antigen specific T cells in diabetes - Lessons from pre-clinical studies and early clinical trials

Antigen-specific immune tolerance promises to provide safe and effective therapies to prevent type 1 diabetes (T1D). Antigen-specific therapy requires two components: well-defined, clinically relevant autoantigens; and safe approaches to inducing tolerance in T cells specific for these antigens. Proinsulin is a critical autoantigen in both NOD mice, based on knockout mouse studies and induction of immune tolerance to proinsulin preventing disease whereas most antigens cannot, and also in human T1D based on proinsulin-specific T cells being found in the islets of affected individuals and the early appearance of insulin autoantibodies. Effective antigen-specific therapies that prevent T1D in humans have not yet been developed although doubt remains about the best molecular form of the antigen, the dose and the route of administration. Preclinical studies suggest that antigen specific therapy is most useful when administered before onset of autoimmunity but this time-window has not been tested in humans until the recent "pre-point" study. There may be a 'window of opportunity' during the neonatal period when 'vaccine' like administration of proinsulin for a short period may be sufficient to prevent diabetes. After the onset of autoimmunity, naive antigen-specific T cells have differentiated into antigen-experienced memory cells and the immune responses have spread to multiple antigens. Induction of tolerance at this stage becomes more difficult although recent studies have suggested generation of antigen-specific TR1 cells can inhibit memory T cells. Preclinical studies are required to identify additional 'help' that is required to induce tolerance to memory T cells and develop protocols for effective therapy in individuals with established autoimmunity.

Active suppression of intestinal CD4(+)TCRαβ(+) T-lymphocyte maturation during the postnatal period

Priming of the mucosal immune system during the postnatal period substantially influences host–microbial interaction and susceptibility to immune-mediated diseases in adult life. The underlying mechanisms are ill defined. Here we show that shortly after birth, CD4 T cells populate preformed lymphoid structures in the small intestine and quickly acquire a distinct transcriptional profile. T-cell recruitment is independent of microbial colonization and innate or adaptive immune stimulation but requires β7 integrin expression. Surprisingly, neonatal CD4 T cells remain immature throughout the postnatal period under homeostatic conditions but undergo maturation and gain effector function on barrier disruption. Maternal SIgA and regulatory T cells act in concert to prevent immune stimulation and maintain the immature phenotype of CD4 T cells in the postnatal intestine during homeostasis. Active suppression of CD4 T-cell maturation during the postnatal period might contribute to prevent auto-reactivity, sustain a broad TCR repertoire and establish life-long immune homeostasis.

The mechanisms governing the ontogeny and maturation of the mucosal immune system during the postnatal period are not well understood. Here the authors characterize the homing kinetic, anatomical distribution and maturation of early intestinal CD4 T cells and provide insights into active T-cell suppression during the postnatal period.

Predicting type 1 diabetes using biomarkers

Clinical type 1 diabetes is preceded by an asymptomatic phase that can be identified by serum islet autoantibodies. This perspective proposes that there is now sufficient evidence to allow a broader use of islet autoantibodies as biomarkers to diagnose type 1 diabetes that is already at an asymptomatic stage, so that attempts to prevent clinical hyperglycemia become a feature of disease management. Prediction would first, therefore, shift toward the use of genetic and other biomarkers to determine the likelihood that islet autoimmunity will develop in an infant, and second, toward metabolic assessment to stage and biomarkers to determine the rate of progression to hyperglycemia in children in whom islet autoimmunity is diagnosed. A case is presented for future comprehensive risk assessment that commences at birth and includes attempts to predict, stage, and prevent initiation and progression of the disease process at multiple stages. The biomarkers required achieving this level of sophistication and dissemination are discussed.

Auto-reactive T cells revised. Overestimation based on methodology?

Autoreactive T cells have been identified in most autoimmune diseases and recently even in healthy individuals. Similar, T cells that recognize either wild-type or tumorspecific tumor antigens have been increasingly reported to develop spontaneously in cancer patients. This insight has become possible mainly due to novel immunoassays which have revolutionized the discovery of rare antigen specific T cells. At present, the major dogma that explains this increasing number of reports of autoreactive T cells is that autoreactive T cells are counteracted by CD4+CD25+ regulatory T (Treg) cells in vivo, in particular in healthy individuals, whereas dysfunction in Tregs or Treg responsiveness may unmask the autoreactive T cell responses in patients with autoimmune diseases. However, studies that identify autoreactive T cells are usually performed by culturing T cells with antigen presenting cells loaded with E. coli produced recombinant protein or unmodified synthetic HLA binding peptides. Our concern is that this approach may ignore the presence of natural genetic variation and post-translational modifications such as e.g. the complex nature of N- and O-linked glycosylation of mammalian proteins. Thus, T cell antigen reactivities identified with unmodified antigens in vitro may in part represent in vitro T cell activation against neo-epitopes and not true in vivo autoreactivity as postulated. This methodological problem may have implications for the interpretation of the frequent reporting of autoreactive T cells in autoimmunity, T cell responses to wild-type tumor antigens in cancer patients and most important for the increasing reports on naïve T cells with specificity against self-antigens in healthy individuals. Here, we discuss and provide examples for the possibility that the experimental methodology applied to document T cell reactivity against unmodified protein or peptide may lead to overinterpretation of the reported frequencies of autoreactive CD4+ and CD8+ T cells.

High diversity in the TCR repertoire of GAD65 autoantigen-specific human CD4+ T cells

Autoreactive CD4(+) T cells are an essential feature of type 1 diabetes mellitus. We applied single-cell TCR α- and β-chain sequencing to peripheral blood GAD65-specific CD4(+) T cells, and TCR α-chain next-generation sequencing to bulk memory CD4(+) T cells to provide insight into TCR diversity in autoimmune diabetes mellitus. TCRs obtained for 1650 GAD65-specific CD4(+) T cells isolated from GAD65 proliferation assays and/or GAD65 557I tetramer staining in 6 patients and 10 islet autoantibody-positive children showed large diversity with 1003 different TCRs identified. TRAV and TRBV gene usage was broad, and the TRBV5.1 gene was most prominent within the GAD65 557I tetramer(+) cells. Limited overlap (<5%) was observed between TCRs of GAD65-proliferating and GAD65 557I tetramer(+) CD4(+) T cells. Few TCRs were repeatedly found in GAD65-specific cells at different time points from individual patients, and none was seen in more than one subject. However, single chains were often shared between patients and used in combination with different second chains. Next-generation sequencing revealed a wide frequency range (<0.00001-1.62%) of TCR α-chains corresponding to GAD65-specific T cells. The findings support minor selection of genes and TCRs for GAD65-specific T cells, but fail to provide strong support for TCR-targeted therapies.

Interleukin-7 and type 1 diabetes

Antigen-experienced T-cells directly target and destroy insulin-producing beta cells in patients with Type 1 diabetes. Consequently, T-cells are also major targets of immunomodulatory strategies that aim to prevent or delay the immune mediated loss of islet beta-cell function. These strategies have had modest success, prompting efforts into better defining the mechanisms that drive the differentiation of quiescent autoreactive clones into pathogenic effector and memory T-cells. Recent and novel findings now indicate that in addition to the classic mechanisms of antigenic recognition, autoreactive T-cell differentiation and expansion can be boosted by the homeostatic cytokine interleukin-7. In this article, we discuss recent evidence of the role of IL-7 mediated T-cell proliferation in the pathogenesis of Type 1 diabetes and the rationale for including immunomodulatory molecules targeting the IL-7/IL-7R axis in immunotherapeutic strategies to control beta-cell autoimmunity.

Maternal microchimerism: friend or foe in type 1 diabetes?

Increased levels of non-inherited maternal HLA alleles have been detected in the periphery of children with type 1 diabetes and an increased frequency of maternal cells have been identified in type 1 diabetes pancreas. It is now clear that the phenotype of these cells is pancreatic, supporting the hypothesis that maternal cells in human pancreas are derived from multipotent maternal progenitors. Here we hypothesize how increased levels of maternal cells could play a role in islet autoimmunity.

The role of the complement system in metabolic organs and metabolic diseases

Emerging evidence points to a close crosstalk between metabolic organs and innate immunity in the course of metabolic disorders. In particular, cellular and humoral factors of innate immunity are thought to contribute to metabolic dysregulation of the adipose tissue or the liver, as well as to dysfunction of the pancreas; all these conditions are linked to the development of insulin resistance and diabetes mellitus. A central component of innate immunity is the complement system. Interestingly, the classical view of complement as a major system of host defense that copes with infections is changing to that of a multi-functional player in tissue homeostasis, degeneration, and regeneration. In the present review, we will discuss the link between complement and metabolic organs, focusing on the pancreas, adipose tissue, and liver and the diverse effects of complement system on metabolic disorders.