Interleukin-21 is required for the development of type 1 diabetes in NOD mice

Interleukin-21 Drives Proliferation and Differentiation of Porcine Memory B Cells into Antibody Secreting Cells

Immunological prevention of infectious disease, especially viral, is based on antigen-specific long-lived memory B cells. To test for cellular proliferation and differentiation factors in swine, an outbred model for humans, CD21+ B cells were activated in vitro with CD40L and stimulated with purported stimulatory cytokines to characterize functional responses. IL-21 induced a 3-fold expansion in total cell numbers with roughly 15% of all B cells differentiating to IgM or IgG antibody secreting cells (ASCs.) However, even with robust proliferation, cellular viability rapidly deteriorated. Therefore, a proliferation inducing ligand (APRIL) and B cell activating factor (BAFF) were evaluated as survival and maintenance factors. BAFF was effective at enhancing the viability of mature B cells as well as ASCs, while APRIL was only effective for ASCs. Both cytokines increased approximately two-fold the amount of IgM and IgG which was secreted by IL-21 differentiated ASCs. Mature B cells from porcine reproductive and respiratory virus (PRRSV) immune and naïve age-matched pigs were activated and treated with IL-21 and then tested for memory cell differentiation using a PRRSV non-structural protein 7 ELISPOT and ELISA. PRRSV immune pigs were positive on both ELISPOT and ELISA while naïve animals were negative on both assays. These results highlight the IL-21-driven expansion and differentiation of memory B cells in vitro without stimulation of the surface immunoglobulin receptor complex, as well as the establishment of a defined memory B cell culture system for characterization of vaccine responses in outbred animals.

CD4+ T cell-dominant insulitis in acute-onset Type 1 diabetes mellitus associated with intraductal papillary mucinous adenoma

The loss of insulin-producing pancreatic β-cells in Type 1 diabetes mellitus (DM) is presumably the result of a T cell-mediated process. In general, CD8⁺ T cells are the predominant lymphocytes in the insulitis lesions, and CD4⁺ T cell-dominant insulitis is very rare. We present a case of a 72-year-old woman presented with excessive thirst and a 3-month history of weight loss. She was in a state of ketosis, and her plasma glucose concentration and HbA1c value were elevated. Moreover, anti-islet autoantibodies were positive, thus acute-onset Type 1 DM was diagnosed. At the time of diagnosis, a tumour was detected in the pancreas; total pancreatectomy was carried out 2 months later. The pathological diagnosis was intraductal papillary mucinous adenoma. Immunohistochemical staining of a sample of non-tumorous pancreatic tissue revealed 13 insulitis lesions infiltrated by both CD4⁺ and CD8⁺ T cells, and interestingly there were more CD4⁺ T cells than CD8⁺ T cells in the lesions. Moreover, B cells and macrophages had also infiltrated the lesions, and these two cell frequencies were both positively correlated with CD4⁺ as well as CD8⁺ T cell frequencies. This was a rare case with acute-onset Type 1 DM characterized by CD4⁺ T cell-dominant insulitis. Proinflammatory cytokines that can promote β-cell apoptosis or CD8⁺ T cell function are reported to be secreted from CD4⁺ T cells. Thus, together with B cells and macrophages, CD4⁺ T cell-associated immune responses may have, directly and/or indirectly, played a role in the pathogenesis of the Type 1 DM in this patient.

Interleukin-21-dependent modulation of T cell antigen receptor reactivity towards low affinity peptide ligands in autoreactive CD8(+) T lymphocytes

IL-21 promotes autoimmune type-1 diabetes (T1D) in NOD mice by facilitating CD4(+) T cell help to CD8(+) T cells. IL-21 also enables autoreactive CD8(+) T cells to respond to weak TCR ligands and induce T1D. Here, we assessed whether IL-21 is essential for T1D induction in a mouse model where the disease can occur independently of CD4 help. In this model, which expresses lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) antigen under the rat insulin promoter (RIP-GP), LCMV infection activates CD8(+) T cells reactive to the GP-derived GP33 peptide that attack pancreatic islets and cause T1D. We show that IL-21 deficiency in RIP-GP mice did not impair T1D induction by LCMV expressing the wildtype GP33 peptide. Surprisingly, LCMV-L6F, expressing a weak peptide mimic of GP33, induced T1D more efficiently in Il21(-/-)RIP-GP mice than in controls. However, LCMV-C4Y expressing a very weak peptide mimic of GP33 did not induce T1D in Il21(-/-) mice, but T cells from the infected mice caused disease in lymphopenic RIP-GP mice upon adoptive transfer. Using Nur77(GFP) reporter mice, we show that CD8(+) T cells from Il21(-/-) mice expressing the GP33-specific transgenic P14 TCR showed increased reactivity towards low affinity TCR ligands. Collectively, our findings show that IL-21 is not always required for T1D induction by autoreactive CD8(+) T cells, and suggest that IL-21 may play an important role in regulating CD8(+) T cell reactivity towards low affinity TCR ligands.

[Roles of interleukin-21 and its receptor in autoimmune diseases]

Interleukin-21 (IL-21) is a new member of the interleukin-2 family. It is mainly synthesized and secreted by the activated of CD4(+) T cells and natural killer T cells. IL-21 receptor (IL-21R) is mainly expressed in T cells, B cells, and natural killer (NK) cells. After binding to its receptor, IL-21 can regulate the activation and proliferation of T cells, B cells, and NK cells through activating JAKs-STATs signaling pathways. As a new immunoregulatory factor, IL-21 and its receptor play important roles in the development and progression of various autoimmune diseases. Regulation of the expression levels of IL-21 and IL-21R and blocking of their signal transduction pathways with blockers may be new treatment options for autoimmune diseases.

[Roles of interleukin-21 and its receptor in autoimmune diseases]

Interleukin-21 (IL-21) is a new member of the interleukin-2 family. It is mainly synthesized and secreted by the activated of CD4(+) T cells and natural killer T cells. IL-21 receptor (IL-21R) is mainly expressed in T cells, B cells, and natural killer (NK) cells. After binding to its receptor, IL-21 can regulate the activation and proliferation of T cells, B cells, and NK cells through activating JAKs-STATs signaling pathways. As a new immunoregulatory factor, IL-21 and its receptor play important roles in the development and progression of various autoimmune diseases. Regulation of the expression levels of IL-21 and IL-21R and blocking of their signal transduction pathways with blockers may be new treatment options for autoimmune diseases.

IL-21 Signaling in Immunity

IL-21 is a type I cytokine produced by T cells and natural killer T cells that has pleiotropic actions on a wide range of immune and non-immune cell types. Since its discovery in 2000, extensive studies on the biological actions of IL-21 have been performed in vitro and in vivo. Recent reports describing patients with primary immunodeficiency caused by mutations of IL21 or IL21R have further deepened our knowledge of the role of this cytokine in host defense. Elucidation of the molecular mechanisms that mediate IL-21's actions has provided the rationale for targeting IL-21 and IL-21 downstream mediators for therapeutic purposes. The use of next-generation sequencing technology has provided further insights into the complexity of IL-21 signaling and has identified transcription factors and co-factors involved in mediating the actions of this cytokine. In this review, we discuss recent advances in the biology and signaling of IL-21 and how this knowledge can be potentially translated into clinical settings.

Mechanisms of autoimmunity in the non-obese diabetic mouse: effector/regulatory cell equilibrium during peak inflammation

Immune imbalance in autoimmune disorders such as type 1 diabetes may originate from aberrant activities of effector cells or dysfunction of suppressor cells. All possible defective mechanisms have been proposed for diabetes-prone species: (i) quantitative dominance of diabetogenic cells and decreased numbers of regulatory T cells, (ii) excessive aggression of effectors and defective function of suppressors, (iii) perturbed interaction between effector and suppressor cells, and (iv) variations in sensitivity to negative regulation. The experimental evidence available to date presents conflicting information on these mechanisms, with identification of perturbed equilibrium on the one hand and negation of critical role of each mechanism in propagation of diabetic autoimmunity on the other hand. In our analysis, there is no evidence that inherent abnormalities in numbers and function of effector and suppressor T cells are responsible for the immune imbalance responsible for propagation of type 1 diabetes as a chronic inflammatory process. Possibly, the experimental tools for investigation of these features of immune activity are still underdeveloped and lack sufficient resolution, in the presence of the extensive biological viability and functional versatility of effector and suppressor elements.

Characterization and Immunoregulatory Properties of Innate Pro-B-Cell Progenitors

Control of T-cell responses can be achieved by several subsets of B cells with immunoregulatory functions, mostly acting by provision of the anti-inflammatory cytokine IL-10 or exhibiting killing properties through Fas ligand (Fas-L) or granzyme B-induced cell death. We herein describe the characterization as well as the cellular and molecular mechanisms mediating the suppressive properties of bone marrow immature innate pro-B cell progenitors that emerge upon transient activation of Toll-like receptor 9. They are licensed by activated T-cell-derived IFN-γ to become suppressive by up-regulating their Fas-L expression and inducing effector CD4(+) T-cell apoptosis. They also up-regulate their own IFN-γ production which dramatically reduces T-cell production of a major pathogenic cytokine, IL-21. A single adoptive transfer of as little as 60,000 of them efficiently prevents the onset of spontaneous type 1 diabetes in recipient nonobese diabetes (NOD) mice, highlighting the remarkable regulatory potency of these so-called CpG-proB cell progenitors compared to regulatory cells of diverse lineages so far described. The CpG-proB cell activity is prolonged in vivo by their differentiation after migration in the pancreas and the spleen into B-cell progeny with high Fas-L expression that can keep up inducing apoptosis of effector T cells in the long term.

In the Intestinal Mucosa of Children With Potential Celiac Disease IL-21 and IL-17A are Less Expressed than in the Active Disease

OBJECTIVES

Potential celiac disease (CD) patients are at an increased risk to developing CD as indicated by positive CD-associated serology. We investigated in duodenal mucosa of such patients the presence of both IL-21 and IL-17A and the role of gliadin peptides and IL-15 in their expression.

METHODS

Duodenal biopsies from 76 active CD, 90 potential CD, and 58 control patients were analyzed for IL-21 and/or IL-17A production by quantitative real-time PCR, immunohistochemistry, flow cytometry, and ELISA. The presence of IL-21 receptor was investigated by western blot. Potential CD duodenal fragments were cultured with gliadin peptides (PTG) and/or IL-15 and the expression/production of IL-21 and IL-17A assessed by quantitative real-time PCR and by immunohistochemistry.

RESULTS

In potential CD, IL-21 was lower than in active CD, in terms of RNA expression (P<0.01), density of lamina propria (LP) IL-21(+) cells (P<0.05), and protein secretion (P<0.05). Also, IL-21R was weakly detectable in potential CD. Several LP cell types produced IL-21 in CD. In potential CD, CD4(+)IL-21(+) cells increased after PMA-ionomycin stimulation and co-produced IFN-γ but not IL-17A. After 24 hours of culture stimulation with PTG, IL-21-producing cells increased but not the ones producing IL-17A. This increase was further enhanced by the addition of IL-15 to culture medium.

CONCLUSIONS

In potential CD, IL-21 is less expressed than in active CD; however, IL-21-producing cells are present and prone to respond after specific stimuli. This suggests a key role of IL-21 in the progression of mucosal damage in CD.

IL-21R signaling is critical for induction of spontaneous experimental autoimmune encephalomyelitis

IL-17-producing CD4+ T cells (Th17 cells) have well-described pathogenic roles in tissue inflammation and autoimmune diseases, such as experimental autoimmune encephalomyelitis (EAE); however, the involvement of IL-21 in these processes has remained controversial. While IL-21 is an essential autocrine amplification factor for differentiation of Th17 cells, the loss of IL-21 or IL-21 receptor (IL-21R) does not protect mice from actively induced EAE. Here, we utilized a transgenic EAE mouse model, in which T and B cells overexpress receptors for myelin oligodendrocyte glycoprotein (MOG) (referred to as 2D2xTH mice), and demonstrated that IL-21 is critical for the development of a variant form of spontaneous EAE in these animals. Il21r deletion in 2D2xTH mice reduced the incidence and severity of spontaneous EAE, which was associated with a defect in Th17 cell generation. Moreover, IL-21R deficiency limited IL-23R expression on Th17 cells and inhibited expression of key molecules involved in the generation of pathogenic Th17 cells. Conversely, loss of IL-23R in 2D2xTH mice resulted in complete resistance to the development of spontaneous EAE. Our data identify a previously unappreciated role for IL-21 in EAE and reveal that IL-21-mediated signaling supports generation and stabilization of pathogenic Th17 cells and development of spontaneous autoimmunity.

Regulatory T Cells in Autoimmune Diabetes: Mechanisms of Action and Translational Potential

Since the discovery of specialized T cells with regulatory function, harnessing the power of these cells to ameliorate autoimmunity has been a major goal. Here we collate the evidence that regulatory T cells (Treg) can inhibit Type 1 diabetes in animal models and humans. We discuss the anatomical sites and molecular mechanisms of Treg suppressive function in the Type 1 diabetes setting, citing evidence that Treg can function in both the pancreatic lymph nodes and within the pancreatic lesion. Involvement of the CTLA-4 pathway, as well as TGF-β and IL-2 deprivation will be considered. Finally, we summarize current efforts to manipulate Treg therapeutically in individuals with Type 1 diabetes. The translation of this research area from bench to bedside is still in its infancy, but the remarkable therapeutic potential of successfully manipulating Treg populations is clear to see.

CD4 T cell differentiation in type 1 diabetes

Susceptibility to type 1 diabetes is associated strongly with human leucocyte antigen (HLA) genes, implicating T cells in disease pathogenesis. In humans, CD8 T cells predominantly infiltrate the islets, yet their activation and propagation probably requires CD4 T cell help. CD4 T cells can select from several differentiation fates following activation, and this choice has profound consequences for their subsequent cytokine production and migratory potential. In turn, these features dictate which other immune cell types T cells interact with and influence, thereby determining downstream effector functions. Obtaining an accurate picture of the type of CD4 T cell differentiation associated with a particular immune-mediated disease therefore constitutes an important clue when planning intervention strategies. Early models of T cell differentiation focused on the dichotomy between T helper type 1 (Th1) and Th2 responses, with type 1 diabetes (T1D) being viewed mainly as a Th1-mediated pathology. However, several additional fate choices have emerged in recent years, including Th17 cells and follicular helper T cells. Here we revisit the issue of T cell differentiation in autoimmune diabetes, highlighting new evidence from both mouse models and patient samples. We assess the strengths and the weaknesses of the Th1 paradigm, review the data on interleukin (IL)-17 production in type 1 diabetes and discuss emerging evidence for the roles of IL-21 and follicular helper T cells in this disease setting. A better understanding of the phenotype of CD4 T cells in T1D will undoubtedly inform biomarker development, improve patient stratification and potentially reveal new targets for therapeutic intervention.

Healthy first-degree relatives of patients with type 1 diabetes exhibit significant differences in basal gene expression pattern of immunocompetent cells compared to controls: expression pattern as predeterminant of autoimmune diabetes

Expression features of genetic landscape which predispose an individual to the type 1 diabetes are poorly understood. We addressed this question by comparing gene expression profile of freshly isolated peripheral blood mononuclear cells isolated from either patients with type 1 diabetes (T1D), or their first-degree relatives or healthy controls. Our aim was to establish whether a distinct type of 'prodiabetogenic' gene expression pattern in the group of relatives of patients with T1D could be identified. Whole-genome expression profile of nine patients with T1D, their ten first-degree relatives and ten healthy controls was analysed using the human high-density expression microarray chip. Functional aspects of candidate genes were assessed using the MetaCore software. The highest number of differentially expressed genes (547) was found between the autoantibody-negative healthy relatives and the healthy controls. Some of them represent genes critically involved in the regulation of innate immune responses such as TLR signalling and CCR3 signalling in eosinophiles, humoral immune reactions such as BCR pathway, costimulation and cytokine responses mediated by CD137, CD40 and CD28 signalling and IL-1 proinflammatory pathway. Our data demonstrate that expression profile of healthy relatives of patients with T1D is clearly distinct from the pattern found in the healthy controls. That especially concerns differential activation status of genes and signalling pathways involved in proinflammatory processes and those of innate immunity and humoral reactivity. Thus, we posit that the study of the healthy relative's gene expression pattern is instrumental for the identification of novel markers associated with the development of diabetes.

Pouring fuel on the fire: Th17 cells, the environment, and autoimmunity

Cytokines play a critical role in controlling the differentiation of CD4 Th cells into distinct subsets, including IL-17-producing Th17 cells. Unfortunately, the incidence of a number of autoimmune diseases, particularly those in which the IL-23/IL-17 axis has been implicated, has risen in the last several decades, suggesting that environmental factors can promote autoimmunity. Here we review the role of cytokines in Th17 differentiation, particularly the role of IL-23 in promoting the differentiation of a pathogenic subset of Th17 cells that potently induce autoimmune tissue inflammation. Moreover, we highlight emerging data that indicate that environmental factors, including the intestinal microbiota and changes in diet, can alter normal cytokine regulation with potent effects on Th17 differentiation and thus promote autoimmunity, which has strong implications for human disease.

Mucosal interleukin-21 mRNA expression level is high in patients with Helicobacter pylori and is associated with the severity of gastritis

Helicobacter pylori (H. pylori) infection is associated with gastritis and marked infiltration of the gastric mucosa by several cytokines secreting inflammatory cells. Different clinical forms of the infection may reflect distinctive patterns of cytokine expression. Interleukin (IL)-17, IL-21, IL-22, and IL-23 have been reported to be involved in H. pylori-induced gastric mucosal inflammation, but the details and relationship to different patterns of inflammation and virulence factors remain unclear. The present study was launched to analyse IL-6 expression in H. pylori-infected and uninfected gastric patients and to investigate its correlation with chronic gastritis among H. pylori-infected patients. Total RNA was extracted from the gastric antrum biopsies of 48 H. pylori-infected patients and 38 H. pylori uninfected patients. Mucosal IL-21 mRNA expression level in H. pylori-infected and uninfected gastric biopsy was determined by real-time PCR. The presence of vacA (vacuolating cytotoxin A) and cagA (cytotoxin associated gene A) virulence factors were evaluated using PCR. Interleukin-21 mRNA expression was significantly high in biopsies of H. pylori-infected patients compared to H. pylori uninfected patients, and the mucosal IL-21 mRNA level was positively correlated with the grade of chronic inflammation. There was no association between virulence factors and IL-21 mRNA expression. We believe that IL-21 might be involved in the pathogenesis of H. pylori and might be an index of the severity of chronic gastritis.

Advances in IL-21 biology - enhancing our understanding of human disease

Cytokines play critical roles in regulating the development and function of immune cells. Cytokines function by binding specific multimeric receptor complexes and activating intracellular signaling pathways that often involve JAKs and STATs. In addition to contributing to immunity, when production of cytokines is perturbed, they can contribute to disease. IL-21 is a pleiotropic cytokine produced predominantly by CD4(+) T cells and NKT cells. Gene-targeting studies in mice and in vitro analyses of human and murine lymphocytes have revealed central roles of IL-21 in regulating effector functions of T cells, NK cells and B cells. However, recent discoveries of loss-of function mutations in IL21 or IL21R in humans have unveiled unexpected roles for IL-21 in immune regulation. This review will focus on recent advances in IL-21 biology that have highlighted its critical role in normal immunity and how dysregulated IL-21 production can lead to immunodeficiency and autoimmune conditions.

ROR inverse agonist suppresses insulitis and prevents hyperglycemia in a mouse model of type 1 diabetes

Hyperglycemia associated with type 1 diabetes is a consequence of immune-mediated destruction of insulin producing pancreatic β-cells. Although it is apparent that both CD8(+) T cells and TH1 cells are key contributors to type 1 diabetes, the function of TH17 cells in disease onset and progression remains unclear. The nuclear receptors retinoic acid receptor-related orphan receptors-α and γt (RORα and RORγt) play critical roles in the development of TH17 cells and ROR-specific synthetic ligands have proven efficacy in several mouse models of autoimmunity. To investigate the roles and therapeutic potential for targeting the RORs in type 1 diabetes, we administered SR1001, a selective RORα/γ inverse agonist, to nonobese diabetic mice. SR1001 significantly reduced diabetes incidence and insulitis in the treated mice. Furthermore, SR1001 reduced proinflammatory cytokine expression, particularly TH17-mediated cytokines, reduced autoantibody production, and increased the frequency of CD4(+)Foxp3(+) T regulatory cells. These data suggest that TH17 cells may have a pathological role in the development of type 1 diabetes, and use of ROR-specific synthetic ligands targeting this cell type may prove utility as a novel treatment for type 1 diabetes.

Follicular helper T cell signature in type 1 diabetes

The strong genetic association between particular HLA alleles and type 1 diabetes (T1D) indicates a key role for CD4+ T cells in disease; however, the differentiation state of the responsible T cells is unclear. T cell differentiation originally was considered a dichotomy between Th1 and Th2 cells, with Th1 cells deemed culpable for autoimmune islet destruction. Now, multiple additional T cell differentiation fates are recognized with distinct roles. Here, we used a transgenic mouse model of diabetes to probe the gene expression profile of islet-specific T cells by microarray and identified a clear follicular helper T (Tfh) cell differentiation signature. Introduction of T cells with a Tfh cell phenotype from diabetic animals efficiently transferred diabetes to recipient animals. Furthermore, memory T cells from patients with T1D expressed elevated levels of Tfh cell markers, including CXCR5, ICOS, PDCD1, BCL6, and IL21. Defects in the IL-2 pathway are associated with T1D, and IL-2 inhibits Tfh cell differentiation in mice. Consistent with these previous observations, we found that IL-2 inhibited human Tfh cell differentiation and identified a relationship between IL-2 sensitivity in T cells from patients with T1D and acquisition of a Tfh cell phenotype. Together, these findings identify a Tfh cell signature in autoimmune diabetes and suggest that this population could be used as a biomarker and potentially targeted for T1D interventions.

Role of immune system in type 1 diabetes mellitus pathogenesis

The immune system is the body's natural defense system against invading pathogens. It protects the body from infection and works to communicate an individual's well-being through a complex network of interconnected cells and cytokines. This system is an associated host defense. An uncontrolled immune system has the potential to trigger negative complications in the host. Type 1 diabetes results from the destruction of pancreatic β-cells by a β-cell-specific autoimmune process. Examples of β-cell autoantigens are insulin, glutamic acid decarboxylase, tyrosine phosphatase, and insulinoma antigen. There are many autoimmune diseases, but type 1 diabetes mellitus is one of the well-characterized autoimmune diseases. The mechanisms involved in the β-cell destruction are still not clear; it is generally believed that β-cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T lymphocytes are involved in the β-cell-specific autoimmune process. It is necessary to determine what exact factors are causing the immune system to become unregulated in such a manner as to promote an autoimmune response.

Linking the circadian rhythm gene Arntl2 to interleukin 21 expression in type 1 diabetes

The circadian rhythm-related aryl hydrocarbon receptor nuclear translocator-like 2 (Arntl2) gene has been identified as a candidate gene for the murine type 1 diabetes locus Idd6.3. Previous studies suggested a role in expansion of CD4(+)CD25(-) T cells, and this then creates an imbalance in the ratio between T-effector and CD4(+)CD25(+) T-regulator cells. Our transcriptome analyses identify the interleukin 21 (IL21) gene (Il21) as a direct target of ARNTL2. ARNTL2 binds in an allele-specific manner to the RNA polymerase binding site of the Il21 promoter and inhibits its expression in NOD.C3H congenic mice carrying C3H alleles at Idd6.3. IL21 is known to promote T-cell expansion, and in agreement with these findings, mice with C3H alleles at Idd6.3 produce lower numbers of CD4(+)IL21(+) and CD4(+) and CD8(+) T cells compared with mice with NOD alleles at Idd6.3. Our results describe a novel and rather unexpected role for Arntl2 in the immune system that lies outside of its predicted function in circadian rhythm regulation.

Interleukin-21: a double-edged sword with therapeutic potential

Interleukin-21 is a cytokine with broad pleiotropic actions that affect the differentiation and function of lymphoid and myeloid cells. Since its discovery in 2000, a tremendous amount has been learned about its biological actions and the molecular mechanisms controlling IL-21-mediated cellular responses. IL-21 regulates both innate and adaptive immune responses, and it not only has key roles in antitumour and antiviral responses but also exerts major effects on inflammatory responses that promote the development of autoimmune diseases and inflammatory disorders. Numerous studies have shown that enhancing or inhibiting the action of IL-21 has therapeutic effects in animal models of a wide range of diseases, and various clinical trials are underway. The current challenge is to understand how to specifically modulate the actions of IL-21 in the context of each specific immune response or pathological situation. In this Review, we provide an overview of the basic biology of IL-21 and discuss how this information has been - and can be - exploited therapeutically.

Beta-cell specific production of IL6 in conjunction with a mainly intracellular but not mainly surface viral protein causes diabetes

Inflammatory mechanisms play a key role in the pathogenesis of type 1 and type 2 diabetes. IL6, a pleiotropic cytokine with impact on immune and non-immune cell types, has been proposed to be involved in the events causing both forms of diabetes and to play a key role in experimental insulin-dependent diabetes development. The aim of this study was to investigate how beta-cell specific overexpression of IL-6 influences diabetes development. We developed two lines of rat insulin promoter (RIP)-lymphocytic choriomeningitis virus (LCMV) mice that also co-express IL6 in their beta-cells. Expression of the viral nucleoprotein (NP), which has a predominantly intracellular localization, together with IL6 led to hyperglycemia, which was associated with a loss of GLUT-2 expression in the pancreatic beta-cells and infiltration of CD11b(+) cells, but not T cells, in the pancreas. In contrast, overexpression of the LCMV glycoprotein (GP), which can localize to the surface, with IL-6 did not lead to spontaneous diabetes, but accelerated virus-induced diabetes by increasing autoantigen-specific CD8(+) T cell responses and reducing the regulatory T cell fraction, leading to increased pancreatic infiltration by CD4(+) and CD8(+) T cells as well as CD11b(+) and CD11c(+) cells. The production of IL-6 in beta-cells acts prodiabetic, underscoring the potential benefit of targeting IL6 in diabetes.

Cytokine regulation of immune tolerance

The immune system provides defenses against invading pathogens while maintaining immune tolerance to self-antigens. This immune homeostasis is harmonized by the direct interactions between immune cells and the cytokine environment in which immune cells develop and function. Herein, we discuss three non-redundant paradigms by which cytokines maintain or break immune tolerance. We firstly describe how anti-inflammatory cytokines exert direct inhibitory effects on immune cells to enforce immune tolerance, followed by discussing other cytokines that maintain immune tolerance through inducing CD4(+)Foxp3(+) regulatory T cells (Tregs), which negatively control immune cells. Interleukin (IL)-2 is the most potent cytokine in promoting the development and survival of Tregs, thereby mediating immune tolerance. IL-35 is mainly produced by Tregs, but its biology function remains to be defined. Finally, we discuss the actions of proinflammatory cytokines that breach immune tolerance and induce autoimmunity, which include IL-7, IL-12, IL-21, and IL-23. Recent genetic studies have revealed the role of these cytokines (or their cognate receptors) in susceptibility to autoimmune diseases. Taken together, we highlight in this review the cytokine regulation of immune tolerance, which will help in further understanding of human diseases that are caused by dysregulated immune system.

Interleukin-21 is a critical regulator of CD4 and CD8 T cell survival during priming under Interleukin-2 deprivation conditions

Optimal T cell activation and expansion require binding of the common gamma-chain (γc) cytokine Interleukin-2 (IL-2) to its cognate receptor that in turn engages a γc/Janus tyrosine kinase (Jak)3 signaling pathway. Because of its restricted expression by antigen-activated T cells and its obligatory role in promoting their survival and proliferation, IL-2 has been considered as a selective therapeutic target for preventing T cell mediated diseases. However, in order to further explore IL-2 targeted therapy, it is critical to precisely understand its role during early events of T cell activation. In this study, we delineate the role of IL-2 and other γc cytokines in promoting the survival of CD4 and CD8 T cells during early phases of priming. Under IL-2 inhibitory conditions (by neutralizing anti-IL-2 mAbs), the survival of activated CD8⁺ T cells was reduced, whereas CD4⁺ T cells remained much more resistant. These results correlated with reduced Bcl-2 expression, and mitochondrial membrane potential in CD8⁺ T cells in comparison to CD4⁺ T cells. However, using transwell co-culture assays we have found that CD4⁺ T cells could rescue the survival of CD8⁺ T cells even under IL-2 deprived conditions via secretion of soluble factors. A cytokine screen performed on CD8⁺ T cells cultured alone revealed that IL-21, another γc cytokine, was capable of rescuing their survival under IL-2 deprivation. Indeed, blocking the IL-21 signaling pathway along with IL-2 neutralization resulted in significantly reduced survival of both CD4⁺ and CD8⁺ T cells. Taken together, we have shown that under IL-2 deprivation conditions, IL-21 may act as the major survival factor promoting T cell immune responses. Thus, investigation of IL-2 targeted therapies may need to be revisited to consider blockade of the IL-21 signaling pathways as an adjunct to provide more effective control of T cell immune responses.

Advances in our understanding of the pathophysiology of Type 1 diabetes: lessons from the NOD mouse

T1D (Type 1 diabetes) is an autoimmune disease caused by the immune-mediated destruction of pancreatic β-cells. Studies in T1D patients have been limited by the availability of pancreatic samples, a protracted pre-diabetic phase and limitations in markers that reflect β-cell mass and function. The NOD (non-obese diabetic) mouse is currently the best available animal model of T1D, since it develops disease spontaneously and shares many genetic and immunopathogenic features with human T1D. Consequently, the NOD mouse has been extensively studied and has made a tremendous contribution to our understanding of human T1D. The present review summarizes the key lessons from NOD mouse studies concerning the genetic susceptibility, aetiology and immunopathogenic mechanisms that contribute to autoimmune destruction of β-cells. Finally, we summarize the potential and limitations of immunotherapeutic strategies, successful in NOD mice, now being trialled in T1D patients and individuals at risk of developing T1D.

Non-antigenic and antigenic interventions in type 1 diabetes

Type 1 diabetes (T1D) results from autoimmune destruction of the pancreatic β-cells. Current T1D therapies are exclusively focused on regulating glycemia rather than the underlying immune response. A handful of trials have sought to alter the clinical course of T1D using various broad immune-suppressors, e.g., cyclosporine A and azathioprine.^1–3 The effect on β-cell preservation was significant, however, these therapies were associated with unacceptable side-effects. In contrast, more recent immunomodulators, such as anti-CD3 and antigenic therapies such as DiaPep277, provide a more targeted immunomodulation and have been generally well-tolerated and safe; however, as a monotherapy there appear to be limitations in terms of therapeutic benefit. Therefore, we argue that this new generation of immune-modifying agents will likely work best as part of a combination therapy. This review will summarize current immune-modulating therapies under investigation and discuss how to move the field of immunotherapy in T1D forward.

Induction of autoimmune diabetes in non-obese diabetic mice requires interleukin-21-dependent activation of autoreactive CD8⁺ T cells

Non-obese diabetic (NOD) mice lacking interleukin (IL)-21 or IL-21 receptor do not develop autoimmune type 1 diabetes (T1D). We have shown recently that IL-21 may promote activation of autoreactive CD8(+) T cells by increasing their antigen responsiveness. To investigate the role of IL-21 in activating diabetogenic CD8(+) T cells in the NOD mouse, we generated IL-21-deficient NOD mice expressing the highly pathogenic major histocompatibility complex (MHC) class-I-restricted 8.3 transgenic T cell receptor (TCR). IL-21 deficiency protected 8.3-NOD mice completely from T1D. CD8(+) T cells from the 8.3-NOD.Il21(-/-) mice showed decreased antigen-induced proliferation but displayed robust antigen-specific cytolytic activity and production of effector cytokines. IL-21-deficient 8.3 T cells underwent efficient homeostatic proliferation, and previous antigen stimulation enabled these cells to cause diabetes in NOD.Scid recipients. The 8.3 T cells that developed in an IL-21-deficient environment showed impaired antigen-specific proliferation in vivo even in IL-21-sufficient mice. These cells also showed impaired IL-2 production and Il2 gene transcription following antigen stimulation. However, IL-2 addition failed to reverse their impaired proliferation completely. These findings indicate that IL-21 is required for efficient initial activation of autoreactive CD8(+) T cells but is dispensable for the activated cells to develop effector functions and cause disease. Hence, therapeutic targeting of IL-21 in T1D may inhibit activation of naive autoreactive CD8(+) T cells, but may have to be combined with other strategies to inhibit already activated cells.

Distinct genetic control of autoimmune neuropathy and diabetes in the non-obese diabetic background

The non-obese diabetic (NOD) mouse is susceptible to the development of autoimmune diabetes but also multiple other autoimmune diseases. Over twenty susceptibility loci linked to diabetes have been identified in NOD mice and progress has been made in the definition of candidate genes at many of these loci (termed Idd for insulin-dependent diabetes). The susceptibility to multiple autoimmune diseases in the NOD background is a unique opportunity to examine susceptibility genes that confer a general propensity for autoimmunity versus susceptibility genes that control individual autoimmune diseases. We previously showed that NOD mice deficient for the costimulatory molecule B7-2 (NOD-B7-2KO mice) were protected from diabetes but spontaneously developed an autoimmune peripheral neuropathy. Here, we took advantage of multiple NOD mouse strains congenic for Idd loci to test the role of these Idd loci the development of neuropathy and determine if B6 alleles at Idd loci that are protective for diabetes will also be for neuropathy. Thus, we generated NOD-B7-2KO strains congenic at Idd loci and examined the development of neuritis and clinical neuropathy. We found that the NOD-H-2(g7) MHC region is necessary for development of neuropathy in NOD-B7-2KO mice. In contrast, other Idd loci that significantly protect from diabetes did not affect neuropathy when considered individually. However, we found potent genetic interactions of some Idd loci that provided almost complete protection from neuritis and clinical neuropathy. In addition, defective immunoregulation by Tregs could supersede protection by some, but not other, Idd loci in a tissue-specific manner in a model where neuropathy and diabetes occurred concomitantly. Thus, our study helps identify Idd loci that control tissue-specific disease or confer general susceptibility to autoimmunity, and brings insight to the Treg-dependence of autoimmune processes influenced by given Idd region in the NOD background.

Interleukin-21 in chronic inflammatory diseases

Interleukin-21 (IL-21), a cytokine produced by various subsets of activated CD4+ T cells, regulates multiple innate and adaptive immune responses. Indeed, IL-21 controls the proliferation and function of CD4+ and CD8+ T lymphocytes, drives the differentiation of B cells into memory cells and Ig-secreting plasma cells, enhances the activity of natural killer cells and negatively regulates the differentiation and activity of regulatory T cells. Moroever, IL-21 can stimulate nonimmune cells to synthesize various inflammatory molecules. Excessive production of IL-21 has been described in many human chronic inflammatory disorders and there is evidence that blockade of IL-21 helps attenuate detrimental responses in mouse models of immune-mediated diseases. In this article we briefly review data supporting the pathogenic role of IL-21 in immune-inflammatory pathologies and discuss the benefits and risks of IL-21 neutralization in patients with such diseases.

Innate pro-B-cell progenitors protect against type 1 diabetes by regulating autoimmune effector T cells

Diverse hematopoietic progenitors, including myeloid populations arising in inflammatory and tumoral conditions and multipotent cells, mobilized by hematopoietic growth factors or emerging during parasitic infections, display tolerogenic properties. Innate immune stimuli confer regulatory functions to various mature B-cell subsets but immature B-cell progenitors endowed with suppressive properties per se or after differentiating into more mature regulatory B cells remain to be characterized. Herein we provide evidence for innate pro-B cells (CpG-proBs) that emerged within the bone marrow both in vitro and in vivo upon Toll-like receptor-9 activation and whose adoptive transfer protected nonobese diabetic mice against type 1 diabetes (T1D). These cells responded to IFN-γ released by activated effector T cells (Teffs), by up-regulating their Fas ligand (FasL) expression, which enabled them to kill Teffs through apoptosis. In turn, IFN-γ derived from CpG-proBs enhanced IFN-γ while dramatically reducing IL-21 production by Teffs. In keeping with the crucial pathogenic role played by IL-21 in T1D, adoptively transferred IFN-γ-deficient CpG-proBs did not prevent T1D development. Additionally, CpG-proBs matured in vivo into diverse pancreatic and splenic suppressive FasL(high) B-cell subsets. CpG-proBs may become instrumental in cell therapy of autoimmune diseases either on their own or as graft complement in autologous stem cell transplantation.

Evaluation of the IL2/IL21, IL2RA and IL2RB genetic variants influence on the endogenous non-anterior uveitis genetic predisposition

Background

Recently, different genetic variants located within the IL2/IL21 genetic region as well as within both IL2RA and IL2RB loci have been associated to multiple autoimmune disorders. We aimed to investigate for the first time the potential influence of the IL2/IL21, IL2RA and IL2RB most associated polymorphisms with autoimmunity on the endogenous non-anterior uveitis genetic predisposition.

Methods

A total of 196 patients with endogenous non-anterior uveitis and 760 healthy controls, all of them from Caucasian population, were included in the current study. The IL2/IL21 (rs2069762, rs6822844 and rs907715), IL2RA (2104286, rs11594656 and rs12722495) and IL2RB (rs743777) genetic variants were genotyped using TaqMan® allelic discrimination assays.

Results

A statistically significant difference was found for the rs6822844 (IL2/IL21 region) minor allele frequency in the group of uveitis patients compared with controls (P-_value=0.02, OR=0.64 CI 95%=0.43-0.94) although the significance was lost after multiple testing correction. Furthermore, no evidence of association with uveitis was detected for the analyzed genetic variants of the IL2RA or IL2RB loci.

Conclusion

Our results indicate that analyzed IL2/IL21, IL2RA and IL2RB polymorphisms do not seem to play a significant role on the non-anterior uveitis genetic predisposition although further studies are needed in order to clear up the influence of these loci on the non-anterior uveitis susceptibility.

The PTPN22 1858T allele but not variants in the proximal promoter region of IL-21 gene is associated with the susceptibility to type 1 diabetes and the presence of autoantibodies in a Brazilian cohort

Interleukin (IL)-21 and protein tyrosine phosphatase non-receptor 22 (PTPN22) regulate lymphocyte function and have been implicated in the pathogenesis of autoimmune diabetes. We sequenced the proximal promoter of the IL-21 gene for the first time and analysed the PTPN22 1858T polymorphism in type 1A diabetes (T1AD) patients and healthy controls (HC). We correlated the frequencies of islet and extra-pancreatic autoantibodies with genotypes from both loci. The case series comprised 612 T1AD patients and 792 HC. Genotyping of PTPN22 C1858T was performed on 434 T1AD patients and 689 HC. The -448 to +83 base pairs (bp) region of the IL-21 gene was sequenced in 309 Brazilian T1AD and 189 HC subjects. We also evaluated human leucocyte antigen (HLA) DR3/DR4 alleles. The frequencies of glutamic acid decarboxylase (GAD65), tyrosine phosphatase-like protein (IA)-2, anti-nuclear antibody (ANA), thyroid peroxidase (TPO), thyroglobulin (TG), thyrotrophin receptor autoantibody (TRAb), anti-smooth muscle (ASM) and 21-hydroxylase (21-OH) autoantibodies were higher in T1AD patients than in HC. The PTPN22 1858T allele was associated with an increased risk for developing T1AD [odds ratio (OR) = 1·94; P < 0·001], particularly in patients of European ancestry, and with a higher frequency of GAD65 and TG autoantibodies. HLA-DR3/DR4 alleles predominated in T1AD patients. A heterozygous allelic IL-21 gene variant (g.-241 T > A) was found in only one patient. In conclusion, only PTPN22 C1858T polymorphism and HLA-DR3 and/or DR4 alleles, but not allelic variants in the 5'-proximal region of the IL-21 gene were associated with T1AD risk. Patients with T1AD had increased frequencies of anti-islet-cell, anti-thyroid, anti-nuclear, anti-smooth muscle and anti-21-OH autoantibodies. The C1858T PTPN22 polymorphism was also associated with a higher frequency of GAD65 and TG autoantibodies.

Excessive Th1 responses due to the absence of TGF-β signaling cause autoimmune diabetes and dysregulated Treg cell homeostasis

TGF-β signaling in T cells is critical for peripheral T-cell tolerance by regulating effector CD4(+) T helper (Th) cell differentiation. However, it is still controversial to what extent TGF-β signaling in Foxp3(+) regulatory T (Treg) cells contributes to immune homeostasis. Here we showed that abrogation of TGF-β signaling in thymic T cells led to rapid type 1 diabetes (T1D) development in NOD mice transgenic for the BDC2.5 T-cell receptor. Disease development in these mice was associated with increased peripheral Th1 cells, whereas Th17 cells and Foxp3(+) Treg cells were reduced. Blocking of IFN-γ signaling alone completely suppressed diabetes development in these mice, indicating a critical role of Th1 cells in this model. Furthermore, deletion of TGF-β signaling in peripheral effector CD4(+) T cells, but not Treg cells, also resulted in rapid T1D development, suggesting that conventional CD4(+) T cells are the main targets of TGF-β to suppress T1D. TGF-β signaling was dispensable for Treg cell function, development, and maintenance, but excessive IFN-γ production due to the absence of TGF-β signaling in naive CD4(+) T cells indirectly caused dysregulated Treg cell homeostasis. We further showed that T cell-derived TGF-β1 was critical for suppression of Th1 cell differentiation and T1D development. These results indicate that autocrine/paracrine TGF-β signaling in diabetogenic CD4(+) T cells, but not Treg cells, is essential for controlling T1D development.

Mechanistic basis of immunotherapies for type 1 diabetes mellitus

Type 1 diabetes (T1D) is an autoimmune disease for which there is no cure. The pancreatic beta cells are the source of insulin that keeps blood glucose normal. When susceptible individuals develop T1D, their beta cells are destroyed by autoimmune T lymphocytes and no longer produce insulin. T1D patients therefore depend on daily insulin injections for survival. Gene therapy in T1D aims at the induction of new islets to replace those that have been destroyed by autoimmunity. A major goal of T1D research is to restore functional beta cell mass while eliminating diabetogenic T cells in the hope of achieving insulin independence. Multiple therapeutic strategies for the generation of new beta cells have been under intense investigations. However, newly formed beta cells would be immediately destroyed by diabetogenic T cells. Therefore, successful islet induction therapy must be supported by potent immunotherapy that will protect the newly formed beta cells. Herein, we will summarize the current information on immunotherapies that aim at modifying T cell response to beta cells. We will first outline the immune mechanisms that underlie T1D development and progression and review the scientific background and rationale for specific modes of immunotherapy. Numerous clinical trials using antigen-specific strategies and immune-modifying drugs have been published, though most have proved too toxic or have failed to provide long-term beta cell protection. To develop an effective immunotherapy, there must be a continued effort on defining the molecular basis that underlies T cell response to pancreatic islet antigens in T1D.

The cytokines IL-21 and GM-CSF have opposing regulatory roles in the apoptosis of conventional dendritic cells

Interleukin-21 (IL-21) has broad actions on T and B cells, but its actions in innate immunity are poorly understood. Here we show that IL-21 induced apoptosis of conventional dendritic cells (cDCs) via STAT3 and Bim, and this was inhibited by granulocyte-macrophage colony-stimulating factor (GM-CSF). ChIP-Seq analysis revealed genome-wide binding competition between GM-CSF-induced STAT5 and IL-21-induced STAT3. Expression of IL-21 in vivo decreased cDC numbers, and this was prevented by GM-CSF. Moreover, repetitive α-galactosylceramide injection of mice induced IL-21 but decreased GM-CSF production by natural killer T (NKT) cells, correlating with decreased cDC numbers. Furthermore, adoptive transfer of wild-type CD4+ T cells caused more severe colitis with increased DCs and interferon-γ (IFN-γ)-producing CD4+ T cells in Il21r(-/-)Rag2(-/-) mice (which lack T cells and have IL-21-unresponsive DCs) than in Rag2(-/-) mice. Thus, IL-21 and GM-CSF exhibit cross-regulatory actions on gene regulation and apoptosis, regulating cDC numbers and thereby the magnitude of the immune response.

Anti-cytokine therapies in T1D: Concepts and strategies

Therapeutic targeting of proinflammatory cytokines is clinically beneficial in several autoimmune disorders. Several of these cytokines are directly implicated in the pathogenesis of type 1 diabetes, suggesting opportunities for design of clinical trials in type 1 diabetes that incorporate selective cytokine blockade as a component of preventative or interventional immunotherapy. The rationale and status of inhibitory therapy directed against IL-1, TNF, IL-12, IL-23, and IL-6 are discussed, towards a goal of using cytokine inhibition as a therapeutic platform to establish an in vivo milieu suitable for modulating the immune response in T1D.

The Emerging Role of Interleukin-21 in Transplantation

Since its discovery in 2000, IL-21 has been shown to play critical roles in the regulation of both innate and adaptive immune responses. IL-21 is produced predominantly by multiple effector CD4⁺ T-cell types [T helper 17 (Th17), follicular helper T (T_FH), and other activated CD4⁺ cells] and NKT cells. In addition to T cell receptor (TCR) signals, the production of IL-21 by activated CD4⁺ T cells is intricately regulated by various extrinsic factors and intrinsic molecules, such as IL-6, IL-21, ICOS, Stat3, IRF4, and Batf. Because IL-21 receptor (IL-21R) is broadly expressed on T, B, NK, and dentritic cells (DCs), IL-21 signaling via Jak-Stat and other pathways has direct pleiotropic effects on their proliferation, differentiation, and effector function. For instance, while Th17 and T_FH cells produce IL-21, IL-21 also facilitates the development of these cells. IL-21-producing T_FH cells are important for the generation and maintenance of germinal centers, and control the differentiation of germinal center B cells and immunoglobulin production. Thus, IL-21R deficiency or IL-21 neutralization with IL-21R-Fc fusion protein prevents B cell-mediated autoimmunity in lupus-prone BXSB.B6-Yaa⁺ or MRL-Fas^lpr mouse models, respectively. IL-21 also enhances expansion and cytotoxicity of CD8⁺ effector T cells. During chronic lymphocytic choriomeningitis viral infection, chronic IL-21 production by antigen-specific CD4⁺ T cells is needed to sustain CD8⁺ T cell function for viral control. IL-21 is also required for the development of T cell-mediated type 1 diabetes in NOD mice, possibly through sustaining effector T cell function in a similar manner. Recently, two papers have shown that IL-21R-Fc prevents both auto- and allo-immune responses after islet transplantation. A timely discussion is thus needed to address the immune actions of IL-21 as well as the therapeutic potential of targeting IL-21 in transplantation.

Pathogenic mechanisms in type 1 diabetes: the islet is both target and driver of disease

Recent advances in our understanding of the pathogenesis of type 1 diabetes have occurred in all steps of the disease. This review outlines the pathogenic mechanisms utilized by the immune system to mediate destruction of the pancreatic beta-cells. The autoimmune response against beta-cells appears to begin in the pancreatic lymph node where T cells, which have escaped negative selection in the thymus, first meet beta-cell antigens presented by dendritic cells. Proinsulin is an important antigen in early diabetes. T cells migrate to the islets via the circulation and establish insulitis initially around the islets. T cells within insulitis are specific for islet antigens rather than bystanders. Pathogenic CD4⁺ T cells may recognize peptides from proinsulin which are produced locally within the islet. CD8⁺ T cells differentiate into effector T cells in islets and then kill beta-cells, primarily via the perforin-granzyme pathway. Cytokines do not appear to be important cytotoxic molecules in vivo. Maturation of the immune response within the islet is now understood to contribute to diabetes, and highlights the islet as both driver and target of the disease. The majority of our knowledge of these pathogenic processes is derived from the NOD mouse model, although some processes are mirrored in the human disease. However, more work is required to translate the data from the NOD mouse to our understanding of human diabetes pathogenesis. New technology, especially MHC tetramers and modern imaging, will enhance our understanding of the pathogenic mechanisms.

Genetic analysis of type 1 diabetes: embryonic stem cells as new tools to unlock biological mechanisms in type 1 diabetes

The nonobese diabetic (NOD) mouse has provided an important animal model for studying the mechanism and genetics of type 1 diabetes over the past 30 years. Arguably, the bio-breeding (BB) rat model may be an even closer phenotypic mimic of the typical human disease. A large number of distinct genetic traits which influence diabetes development have been defined through an extraordinary effort, most conspicuously in the mouse model. However, in both NOD and BB models the lack of availability of robust means for experimental genetic manipulation has restricted our understanding of the mechanisms underlying this spontaneous autoimmune disease. Recent developments in the derivation of embryonic stem (ES) cells have the potential to transform this picture. We argue here that targeting of NOD strain ES cells can bring much needed certainty to our present understanding of the genetics of type 1 diabetes in the NOD mouse. In addition, ES cells can play important roles in the future, in both the NOD mouse and BB rat models, through the generation of new tools to investigate the mechanisms by which genetic variation acts to promote diabetes.

The immunosuppressive role of adenosine A2A receptors in ischemia reperfusion injury and islet transplantation

Activation of adenosine A2A receptors (A2AR) reduces inflammation by generally inhibiting the activation of pro-inflammatory cells, decreasing endothelial adhesion molecule expression and reducing the release of proinflammatory cytokine mediators. Numerous preclinical studies using selective A2AR agonists, antagonists, A2AR knockout as well as chimeric mice have suggested the therapeutic potential of A2AR agonists for the treatment of ischemia reperfusion injury (IRI) and autoimmune diseases. This review summarizes the immunosuppressive actions of A2AR agonists in murine IRI models of liver, kidney, heart, lung and CNS, and gives details on the cellular effects of A2AR activation in neutrophils, macrophages, dendritic cells, natural killer cells, NKT cells, T effector cells and CD4+CD25+FoxP3+ T regulatory cells. This is discussed in the context of cytokine mediators involved in inflammatory cascades. Whilst the role of adenosine receptor agonists in various models of autoimmune disease has been well-documented, very little information is available regarding the role of A2AR activation in type 1 diabetes mellitus (T1DM). An overview of the pathogenesis of T1DM as well as early islet graft rejection in the immediate peri-transplantation period offers insight regarding the use of A2AR agonists as a beneficial intervention in clinical islet transplantation, promoting islet graft survival, minimizing early islet loss and reducing the number of islets required for successful transplantation, thereby increasing the availability of this procedure to a greater number of recipients. In summary, the use of A2AR agonists as a clinical intervention in IRI and as an adjunct to clinical immunesuppressive regimen in islet transplantation is highlighted.

B-cell cross-presentation of autologous antigen precipitates diabetes

For autoimmune conditions like type 1 diabetes to progress, self-reactive CD8⁺ T cells would need to interact with peptide-antigen cross-presented on the surface of antigen-presenting cells in a major histocompatibility complex (MHC) class I-restricted fashion. However, the mechanisms by which autoantigen is cross-presented remain to be identified. In this study, we show cross-presentation of islet-derived autoantigens by B cells. B cells engage self-reactive CD8⁺ T cells in the pancreatic lymph node, driving their proliferative expansion and differentiation into granzyme B⁺interferon-γ⁺lysosomal-associated membrane protein 1⁺ effector cells. B-cell cross-presentation of insulin required proteolytic cleavage and endosomal localization and was sensitive to inhibitors of protein trafficking. Absent B-cell MHC class I, or B-cell receptor restriction to an irrelevant specificity, blunted the expansion of self-reactive CD8⁺ T cells, suggesting B-cell antigen capture and presentation are critical in vivo events for CD8 activation. Indeed, the singular loss of B-cell MHC class I subverted the conversion to clinical diabetes in NOD mice, despite the presence of a pool of activated, and B cell-dependent, interleukin-21-expressing Vβ4⁺CD4⁺ T cells. Thus, B cells govern the transition from clinically silent insulitis to frank diabetes by cross-presenting autoantigen to self-reactive CD8⁺ T cells.

Low doses of anti-CD3, ciclosporin A and the vitamin D analogue, TX527, synergise to delay recurrence of autoimmune diabetes in an islet-transplanted NOD mouse model of diabetes

AIMS/HYPOTHESIS

Anti-CD3 monoclonal antibodies remain the most promising immune therapy for reversing recent-onset type 1 diabetes. However, current clinical trials have revealed their major drawback, namely the narrow therapeutic window in which low doses are ineffective and higher doses that preserve functional beta cell mass cause side effects. Strategies that sidestep these limitations while preserving or improving anti-CD3's therapeutic efficiency are essential. We hypothesised that combining a potent vitamin D(3) analogue (TX527), ciclosporin A (CsA) and anti-CD3 would act to lower the dose while maintaining or even boosting therapeutic efficacy to counteract autoimmune destruction of transplanted islets.

METHODS

This study involved the use of syngeneic islet transplantation, immunofluorescence microscopy, immune phenotyping by flow cytometry, RT-PCR analysis, and in vitro and in vivo suppression assays.

RESULTS

Combination therapy with TX527, CsA and anti-CD3 was well tolerated on the basis of weight, bone and calcium variables. Remarkably, combining all three agents at sub-therapeutic doses greatly reduced recurrent autoimmune responses to a grafted islet mass (mean ± SEM: 79.5 ± 18.6 days; p < 0.01), by far exceeding the therapeutic efficacy of monotherapy (24.8 ± 7.3 days for anti-CD3) and dual therapy (25.5 ± 12.4 days for anti-CD3+CsA). Combination therapy surpassed anti-CD3 monotherapy in reducing islet infiltration by effector/memory phenotype CD8(+) T cells, as well as by reducing proinflammatory cytokine responses and increasing the frequency of T regulatory cells that were functional in vitro and in vivo, and acted in a cytotoxic T lymphocyte antigen 4-dependent manner.

CONCLUSIONS/INTERPRETATION

Combining the immunomodulatory actions of anti-CD3 mAb with CsA and the vitamin D(3) analogue, TX527, delivers therapeutic efficacy in an islet-transplanted NOD mouse model of diabetes.