Histopathology of type 1 diabetes: old paradigms and new insights

The interplay between cytokines, inflammation, and antioxidants: mechanistic insights and therapeutic potentials of various antioxidants and anti-cytokine compounds

Cytokines regulate immune responses essential for maintaining immune homeostasis, as deregulated cytokine signaling can lead to detrimental outcomes, including inflammatory disorders. The antioxidants emerge as promising therapeutic agents because they mitigate oxidative stress and modulate inflammatory pathways. Antioxidants can potentially ameliorate inflammation-related disorders by counteracting excessive cytokine-mediated inflammatory responses. A comprehensive understanding of cytokine-mediated inflammatory pathways and the interplay with antioxidants is paramount for developing natural therapeutic agents targeting inflammation-related disorders and helping to improve clinical outcomes and enhance the quality of life for patients. Among these antioxidants, curcumin, vitamin C, vitamin D, propolis, allicin, and cinnamaldehyde have garnered attention for their anti-inflammatory properties and potential therapeutic benefits. This review highlights the interrelationship between cytokines-mediated disorders in various diseases and therapeutic approaches involving antioxidants.

Deep Learning for Type 1 Diabetes Mellitus Diagnosis Using Infrared Quantum Cascade Laser Spectroscopy

An estimated 10.5% of the world’s population aged 20–79 years are currently living with diabetes in 2021. An urgent task is to develop a non-invasive express-diagnostics of diabetes with high accuracy. Type 1 diabetes mellitus (T1DM) diagnostic method based on infrared laser spectroscopy of human exhaled breath is described. A quantum cascade laser emitting in a pulsed mode with a peak power of up to 150 mW in the spectral range of 5.3–12.8 μm and Herriot multipass gas cell with an optical path length of 76 m were used. We propose a method for collecting and drying an exhaled human air sample and have measured 1200 infrared exhaled breath spectra from 60 healthy volunteers (the control group) and 60 volunteers with confirmed T1DM (the target group). A 1-D convolutional neural network for the classification of healthy and T1DM volunteers with an accuracy of 99.7%, recall 99.6% and AUC score 99.9% was used. The demonstrated results require clarification on a larger dataset and series of clinical studies and, further, the method can be implemented in routine medical practice.

Phagocytosis and Efferocytosis by Resident Macrophages in the Mouse Pancreas

The tissue microenvironment in the mouse pancreas has been shown to promote very different polarizations of resident macrophages with islet-resident macrophages displaying an inflammatory "M1" profile and macrophages in the exocrine tissue mostly displaying an alternatively activated "M2" profile. The impact of this polarization on tissue homeostasis and diabetes development is unclear. In this study, the ability of pancreas-resident macrophages to phagocyte bacterial and endogenous debris was investigated. Mouse endocrine and exocrine tissues were separated, and tissue-resident macrophages were isolated by magnetic immunolabeling. Isolated macrophages were subjected to flow cytometry for polarization markers and qPCR for phagocytosis-related genes. Functional in vitro investigations included phagocytosis and efferocytosis assays using pH-sensitive fluorescent bacterial particles and dead fluorescent neutrophils, respectively. Intravital confocal imaging of in situ phagocytosis and efferocytosis in the pancreas was used to confirm findings in vivo. Gene expression analysis revealed no significant overall difference in expression of most phagocytosis-related genes in islet-resident vs. exocrine-resident macrophages included in the analysis. In this study, pancreas-resident macrophages were shown to differ in their ability to phagocyte bacterial and endogenous debris depending on their microenvironment. This difference in abilities may be one of the factors polarizing islet-resident macrophages to an inflammatory state since phagocytosis has been found to imprint macrophage heterogeneity. It remains unclear if this difference has any implications in the development of islet dysfunction or autoimmunity.

Enteroviral Pathogenesis of Type 1 Diabetes: The Role of Natural Killer Cells

Enteroviruses, especially group B coxsackieviruses (CV-B), have been associated with the development of chronic diseases such as type 1 diabetes (T1D). The pathological mechanisms that trigger virus-induced autoimmunity against islet antigens in T1D are not fully elucidated. Animal and human studies suggest that NK cells response to CV-B infection play a crucial role in the enteroviral pathogenesis of T1D. Indeed, CV-B-infected cells can escape from cytotoxic T cells recognition and destruction by inhibition of cell surface expression of HLA class I antigen through non-structural viral proteins, but they can nevertheless be killed by NK cells. Cytolytic activity of NK cells towards pancreatic beta cells persistently-infected with CV-B has been reported and defective viral clearance by NK cells of patients with T1D has been suggested as a mechanism leading to persistence of CV-B and triggering autoimmunity reported in these patients. The knowledge about host antiviral defense against CV-B infection is not only crucial to understand the susceptibility to virus-induced T1D but could also contribute to the design of new preventive or therapeutic approaches for individuals at risk for T1D or newly diagnosed patients.

Suppression of diabetes by accumulation of non-islet-specific CD8+ effector T cells in pancreatic islets

The inflammatory lesion at the pancreatic islet in type 1 diabetes (T1D) contains a heterogeneous infiltrate of T cells. In human and mouse studies, a large majority (98 to 99%) of the cytotoxic CD8⁺ T cells (CTLs) within islets are not specific to any islet antigen and are thought to passively add to tissue damage. We show by intravital confocal microscopy the opposite, immune-regulatory function of this cohort of CTLs. Diabetes did not develop in mice with islets showing high levels of infiltration of non-islet-specific CTLs not recognizing local antigens. Accumulation of such CTLs resulted in lower activation and proliferation of islet-specific CTLs, leading them to enter a state of unresponsiveness due to limited access to antigens at the inflammatory lesion. This nonspecific suppression by nonautoreactive CTLs was recapitulated in a model of viral meningitis, may explain viral interference in autoimmunity, and provides insight into the regulation of organ-specific autoimmune responses.

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.

What's in a Name? Classification of Diabetes Mellitus in Veterinary Medicine and Why It Matters

Diabetes Mellitus (DM) is a syndrome caused by various etiologies. The clinical manifestations of DM are not indicative of the cause of the disease, but might be indicative of the stage and severity of the disease process. Accurately diagnosing and classifying diabetic dogs and cats by the underlying disease process is essential for current and future studies on early detection, prevention, and treatment of underlying disease. Here, we review the current etiology-based classification of DM and definitions of DM types in human medicine and discuss key points on the pathogenesis of each DM type and prediabetes. We then review current evidence for application of this etiology-based classification scheme in dogs and cats. In dogs, we emphasize the lack of consistent evidence for autoimmune DM (Type 1) and the possible importance of other DM types such as DM associated with exocrine pancreatic disease. While most dogs are first examined because of DM in an insulin-dependent state, early and accurate diagnosis of the underlying disease process could change the long-term outcome and allow some degree of insulin independence. In cats, we review the appropriateness of using the umbrella term of Type 2 DM and differentiating it from DM secondary to other endocrine disease like hypersomatotropism. This differentiation could have crucial implications on treatment and prognosis. We also discuss the challenges in defining and diagnosing prediabetes in cats.

Neoantigens and Microenvironment in Type 1 Diabetes: Lessons from Antitumor Immunity

Type 1 diabetes (T1D) is characterized by the selective and progressive destruction of insulin-producing beta cells by the immune system. An incomplete thymic selection against self-reactive islet antigens partly explains how these T cells reach the periphery and become diabetogenic. Increasing evidence suggest that beta cells themselves also participate to their own demise by generating neoepitopes that could be recognized by the immune surveillance machinery. In this regard, these T cells eradicate self-tissue by mechanisms analogous to a classical antitumor response. Cancer immunotherapy has exploited mutations and transcriptional and translational errors to trigger a specific antitumor response. In this opinion article, we aim at merging insight in antitumor immunology and autoimmunity to reveal processes that had previously been ignored to create beta cell-specific neoantigens.

Childhood Bereavement and Type 1 Diabetes: a Danish National Register Study

BACKGROUND

Death of a close family member such as a parent or a sibling can cause prolonged stress and changes in the family structure that may have extensive social and health effects on a young child. The aim of this paper is to examine the rate of type 1 diabetes following bereavement due to death of a first-degree family member in early life.

METHODS

We used data from the Danish Civil Registration System (CRS) to identify singleton births in Denmark born 1 January 1980 through 31 December 2005, n = 1 740 245 and their next of kin. We categorised children as exposed to bereavement if they lost a mother, father or sibling from age 5 years onwards, the remaining children were considered unexposed. Children were followed until first diagnosis of diabetes, death, emigration, or 31 December 2010. We estimated incidence rate ratios (IRRs) from birth using log-linear Poisson regression models with person-years as an offset variable. Exposed children were followed up for an average of 9.1 years [standard deviation (SD) 6.7] and unexposed children were followed up for an average of 12.3 years (SD 7.3).

RESULTS

In our sample 94 943 children were exposed to bereavement, and 6110 cases of type 1 diabetes were identified. Bereavement was associated with an increased rate of type 1 diabetes when exposure onset began after 11 years of age (adjusted IRR 1.28, 95% confidence interval 1.08, 1.51).

CONCLUSION

We found some evidence to indicate an increase in the rate of type 1 diabetes among children exposed to bereavement when exposure occurred after 11 years of age.

Perforin facilitates beta cell killing and regulates autoreactive CD8+ T-cell responses to antigen in mouse models of type 1 diabetes

In type 1 diabetes, cytotoxic CD8(+) T lymphocytes (CTLs) directly interact with pancreatic beta cells through major histocompatibility complex class I. An immune synapse facilitates delivery of cytotoxic granules, comprised mainly of granzymes and perforin. Perforin deficiency protects the majority of non-obese diabetic (NOD) mice from autoimmune diabetes. Intriguingly perforin deficiency does not prevent diabetes in CD8(+) T-cell receptor transgenic NOD8.3 mice. We therefore investigated the importance of perforin-dependent killing via CTL-beta cell contact in autoimmune diabetes. Perforin-deficient CTL from NOD mice or from NOD8.3 mice were significantly less efficient at adoptive transfer of autoimmune diabetes into NODRag1(-/-) mice, confirming that perforin is essential to facilitate beta cell destruction. However, increasing the number of transferred in vitro-activated perforin-deficient 8.3 T cells reversed the phenotype and resulted in diabetes. Perforin-deficient NOD8.3 T cells were present in increased proportion in islets, and proliferated more in response to antigen in vivo indicating that perforin may regulate the activation of CTLs, possibly by controlling cytokine production. This was confirmed when we examined the requirement for direct interaction between beta cells and CD8(+) T cells in NOD8.3 mice, in which beta cells specifically lack major histocompatibility complex (MHC) class I through conditional deletion of β2-microglobulin. Although diabetes was significantly reduced, 40% of these mice developed diabetes, indicating that NOD8.3 T cells can kill beta cells in the absence of direct interaction. Our data indicate that although perforin delivery is the main mechanism that CTL use to destroy beta cells, they can employ alternative mechanisms to induce diabetes in a perforin-independent manner.

Expression of human leukocyte antigen class I in endocrine and exocrine pancreatic tissue at onset of type 1 diabetes

The cause of type 1 diabetes remains unknown. To dissect the link between hyperexpression of human leukocyte antigen (HLA) class I on the islet cells, we examined its expression in subjects with recent-onset type 1 diabetes. IHC showed seemingly pronounced hyperexpression in subjects with recent-onset type 1 diabetes, as well as in some nondiabetic subjects. In all subjects, HLA class I expression on exocrine tissue was low. However, no difference in the level of HLA class I expression was found between islet and exocrine tissue using Western blot, flow cytometry, real-time quantitative PCR, or RNA sequencing analyses. Also, the level of HLA class I expression on the messenger level was not increased in islets from subjects with recent-onset type 1 diabetes compared with that in nondiabetic subjects. Consistently, the HLA class I specific enhanceosome (NLRC5) and related transcription factors, as well as interferons, were not enhanced in islets from recent-onset type 1 diabetic subjects. In conclusion, a discrepancy in HLA class I expression in islets assessed by IHC was observed compared with that using quantitative techniques showing similar expression of HLA class I in islets and exocrine tissue in subjects with recent-onset type 1 diabetes, nor could any differences be found between type 1 diabetic and nondiabetic subjects. Results presented provide important clues for a better understanding on how this complex disease develops.

Endocrine Pancreas in Cats With Diabetes Mellitus

Pancreatic amyloidosis and loss of α and β cells have been shown to occur in cats with diabetes mellitus, although the number of studies currently available is very limited. Furthermore, it is not known whether pancreatic islet inflammation is a common feature. The aims of the present study were to characterize islet lesions and to investigate whether diabetic cats have inflammation of the pancreatic islets. Samples of pancreas were collected postmortem from 37 diabetic and 20 control cats matched for age, sex, breed, and body weight. Histologic sections were stained with hematoxylin and eosin and Congo red; double labeled for insulin/CD3, insulin/CD20, insulin/myeloperoxidase, insulin/proliferating cell nuclear antigen, and glucagon/Ki67; and single labeled for amylin and Iba1. Mean insulin-positive cross-sectional area was approximately 65% lower in diabetic than control cats ( P = .009), while that of amylin and glucagon was similar. Surprisingly, amyloid deposition was similar between groups ( P = .408). Proliferation of insulin- and glucagon-positive cells and the number of neutrophils, macrophages, and T (CD3) and B (CD20) lymphocytes in the islets did not differ. The presence of T and B lymphocytes combined tended to be more frequent in diabetic cats ( n = 8 of 37; 21.6%) than control cats ( n = 1 of 20; 5.0%). The results confirm previous observations that loss of β cells but not α cells occurs in diabetic cats. Islet amyloidosis was present in diabetic cats but was not greater than in controls. A subset of diabetic cats had lymphocytic infiltration of the islets, which might be associated with β-cell loss.

Analysis of peri-islet CD45-positive leucocytic infiltrates in long-standing type 1 diabetic patients

AIMS/HYPOTHESIS

The role of peri-islet CD45-positive leucocytes, as one component of insulitis, in beta cell death during human type 1 diabetes remains unclear. We undertook a case study, comparing and quantifying leucocytes in the peri- and intra-islet areas in insulin-positive and -negative islets, to assess whether peri-islet leucocytes are pathogenic to beta cells during type 1 diabetes.

METHODS

Pancreatic sections from 12 diabetic patients (0.25-12 years of disease) and 13 non-diabetic individuals with and without autoantibodies were triple-immunostained for islet leucocytes, insulin and glucagon cells. Islets were graded for insulitis, enumerated and mapped for the spatial distribution of leucocytes in peri- and intra-islet areas in relation to insulin- and glucagon-immunopositive cells.

RESULTS

In the non-diabetic autoantibody-negative group, the percentage of islets with insulitis was either absent or <1% in five out of eight cases and ranged from 1.3% to 19.4% in three cases. In the five non-diabetic autoantibody-positive cases, it varied from 1.5% to 16.9%. In the diabetic group, it was <1% in one case and 1.1-26.9% in 11 cases, with insulitis being absent in 68% of insulin-positive islets. Peri-islet leucocytes were more numerous than intra-islet leucocytes in islets with insulin positivity. Increasing numbers of exocrine leucocytes in non-diabetic autoantibody-positive and diabetic donors were also present.

CONCLUSIONS/INTERPRETATION

The prominence of peri-islet leucocytes in insulin-positive islets in most long-standing diabetic individuals suggests that they may be pathogenic to residual beta cells. Increasing numbers of leucocytes in the exocrine region may also participate in the pathogenesis of type 1 diabetes.

NF-κB and STAT1 control CXCL1 and CXCL2 gene transcription

Diabetes mellitus results from immune cell invasion into pancreatic islets of Langerhans, eventually leading to selective destruction of the insulin-producing β-cells. How this process is initiated is not well understood. In this study, we investigated the regulation of the CXCL1 and CXCL2 genes, which encode proteins that promote migration of CXCR2(+) cells, such as neutrophils, toward secreting tissue. Herein, we found that IL-1β markedly enhanced the expression of the CXCL1 and CXCL2 genes in rat islets and β-cell lines, which resulted in increased secretion of each of these proteins. CXCL1 and CXCL2 also stimulated the expression of specific integrin proteins on the surface of human neutrophils. Mutation of a consensus NF-κB genomic sequence present in both gene promoters reduced the ability of IL-1β to promote transcription. In addition, IL-1β induced binding of the p65 and p50 subunits of NF-κB to these consensus κB regulatory elements as well as to additional κB sites located near the core promoter regions of each gene. Additionally, serine-phosphorylated STAT1 bound to the promoters of the CXCL1 and CXCL2 genes. We further found that IL-1β induced specific posttranslational modifications to histone H3 in a time frame congruent with transcription factor binding and transcript accumulation. We conclude that IL-1β-mediated regulation of the CXCL1 and CXCL2 genes in pancreatic β-cells requires stimulus-induced changes in histone chemical modifications, recruitment of the NF-κB and STAT1 transcription factors to genomic regulatory sequences within the proximal gene promoters, and increases in phosphorylated forms of RNA polymerase II.

The changing landscape of type 1 diabetes: recent developments and future frontiers

Type 1 diabetes (T1D) research has made great strides over the past decade with advances in understanding the pathogenesis, natural history, candidate environmental exposures, exposure triggering time, disease prediction, and diagnosis. Major monitoring efforts have provided baseline historical measures, leading to better epidemiological studies incorporating longitudinal biosamples (ie, biobanks), which have allowed for new technologies ('omics') to further expose the etiological agents responsible for the initiation, progression, and eventual clinical onset of T1D. These new frontiers have brought forth high-dimensionality data, which have furthered the evidence of the heterogeneous nature of T1D pathogenesis and allowed for a more mechanistic approach in understanding the etiology of T1D. This review will expand on the most recent advances in the quest for T1D determinants, drawing upon novel research tools that epidemiology, genetics, microbiology, and immunology have provided, linking them to the major hypotheses associated with T1D etiology, and discussing the future frontiers.

Protection of islet grafts through transforming growth factor-β-induced tolerogenic dendritic cells

In type 1 diabetes, the insulin-producing β-cells are destroyed by the immune system. One way of restoring glucose control is to transplant β-cells from a donor. Although this procedure may restore endogenous insulin production, immunosuppressive treatment is needed to prevent the recipient from rejecting the donor-derived islets. We investigated the possibilities of transient expression of the immunosuppressive cytokine transforming growth factor (TGF)-β within islets to achieve long-term graft tolerance. We found that brief expression of TGF-β prevented rejection of syngeneic islets, that there was reduction of dendritic cell (DC) activation in the graft, and that there was reduced reactivation of T cells in the graft-draining lymph nodes. In vitro exposure of bone marrow-derived DCs to TGF-β reduced expression of costimulatory molecules CD80 and CD86, as well as production of proinflammatory cytokines such as interleukin-12 p70 in DCs, but did not alter levels of major histocompatibility complex classes I and II. Furthermore, the capacity of TGF-β-treated bone marrow-derived DCs to activate both CD4(+) and CD8(+) T cells was reduced. Adding TGF-β-conditioned tolerogenic DCs to the grafted islets led to long-term survival of the graft, demonstrating that TGF-β-induced tolerogenic DCs can provide an effective means to restore immune tolerance in an already established autoimmune disease.

Understanding type 1 diabetes: etiology and models

Type 1 diabetes is a complex disease involving a combination of factors, such as genetic susceptibility, immunologic dysregulation and exposure to environmental triggers. Animal models serve an important function both in elucidating the pathophysiology and preliminary screening of antidiabetic molecules. Hence, the development of models for type 1 diabetes can be broadly divided into 3 categories, namely: identification of spontaneously developing type 1 diabetes mellitus strains, creating diabetes-prone species through gene transfer techniques and forced destruction of islet cells through chemical or surgical means. This review discusses the models used to study type 1 diabetes with special emphasis on genetics.

Virus infections in type 1 diabetes

The precise etiology of type 1 diabetes (T1D) is still unknown, but viruses have long been suggested as a potential environmental trigger for the disease. However, despite decades of research, the body of evidence supporting a relationship between viral infections and initiation or acceleration of islet autoimmunity remains largely circumstantial. The most robust association with viruses and T1D involves enterovirus species, of which some strains have the ability to induce or accelerate disease in animal models. Several hypotheses have been formulated to mechanistically explain how viruses may affect islet autoimmunity and β-cell decay. The recent observation that certain viral infections, when encountered at the right time and infectious dose, can prevent autoimmune diabetes illustrates that potential relationships may be more complex than previously thought. Here, we provide a concise summary of data obtained in mouse models and humans, and identify future avenues toward a better characterization of the association between viruses and T1D.

Immunobiology of beta-cell destruction

Type 1 diabetes is a chronic disease characterized by severe insulin deficiency and hyperglycemia, due to autoimmune destruction of pancreatic islets of Langerhans. A susceptible genetic background is necessary, but not sufficient, for the development of the disease. Epidemiological and clinical observations underscore the importance of environmental factors as triggers of type 1 diabetes, currently under investigation. Islet-specific autoantibodies precede clinical onset by months to years and are established tools for risk prediction, yet minor players in the pathogenesis of the disease. Many efforts have been made to elucidate disease-relevant defects in the key immune effectors of islet destruction, from the early failure of specific tolerance to the vicious circle of destructive insulitis. However, the events triggering islet autoimmunity as well as the transition to overt diabetes are still largely unknown, making prevention and treatment strategies still a challenge.

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.

Clinical potential of antigen-specific therapies in type 1 diabetes

In type 1 diabetes (T1D), pancreatic beta-cells are attacked and destroyed by the immune system, which leads to a loss of endogenous insulin secretion. The desirable outcome of therapeutic intervention in autoimmune diseases is the restoration of immune tolerance to prevent organ damage. Past trials with immune suppressive drugs highlight the fact that T1D is in principle a curable condition. However, the barrier in T1D therapy in terms of drug safety is set particularly high because of the predominantly young population and the good prognosis associated with modern exogenous insulin therapy. Thus, there is a general consensus that chronic immune suppression is associated with unacceptable long-term safety risks. On the other hand, immune-modulatory biologicals have recently failed to confer significant protection in phase 3 clinical trials. However, the concept of antigen-specific tolerization may offer a unique strategy to safely induce long-term protection against T1D. In this review, we analyze the potential reasons for the failure of the different tolerization therapies, and describe how the concept of antigen-specific toleraization may overcome the obstacles associated with clinical therapy in T1D.

ZnT8 is a major CD8+ T cell-recognized autoantigen in pediatric type 1 diabetes

Type 1 diabetes results from the destruction of β-cells by an autoimmune T-cell response assisted by antigen-presenting B cells producing autoantibodies. CD8(+) T-cell responses against islet cell antigens, thought to play a central role in diabetes pathogenesis, can be monitored using enzyme-linked immunosorbent spot (ELISpot) assays. However, such assays have been applied to monitoring of adult patients only, leaving aside the large and increasing pediatric patient population. The objective of this study was twofold: 1) to develop a CD8(+) T-cell interferon-γ ELISpot assay for pediatric patients and 2) to determine whether zinc transporter 8 (ZnT8), a recently described target of autoantibodies in a majority of patients, is also recognized by autoreactive CD8(+) T cells. Using DNA immunization of humanized mice, we identified nine HLA-A2-restricted ZnT8 epitopes. Among 36 HLA-A2(+) children with diabetes, 29 responded to ZnT8 epitopes, whereas only 3 of 16 HLA-A2(+) control patients and 0 of 17 HLA-A2(-) control patients responded. Some single ZnT8 epitopes performed as well as the group of epitopes in discriminating between patients and control individuals. Thus, ZnT8 is a major CD8(+) T-cell autoantigen, and ELISpot assays display similar performance in adult and pediatric type 1 diabetes.

Viruses and cytotoxic T lymphocytes in type 1 diabetes

Histopathological studies on pancreas tissues from individuals with recent-onset type 1 diabetes (T1D) consistently find that CD8 T cells substantially contribute to the formation of islet lesions. CD8 T cells reactive against islet-associated antigens can also be found in blood samples from T1D patients. Mechanistic studies on the pathogenic role of this T cell subset have mostly focused on two animal models, i.e., the non-obese diabetic mouse and the virally induced rat insulin promoter-lymphocytic choriomeningitis virus model. Data were obtained in support of a role for viral infection in expanding a population of diabetogenic cytotoxic T lymphocytes. In view of the theorized association of viral infection with initiation of islet autoimmunity and progression to clinically overt disease, CD8 T cells thus represent an attractive target for immunotherapy. We will review here arguments in favor of a pivotal role for CD8 T cells in driving T1D development and speculate on etiologic agents that may provoke their aberrant activation.

Demonstration of islet-autoreactive CD8 T cells in insulitic lesions from recent onset and long-term type 1 diabetes patients

In situ tetramer staining reveals the presence of islet antigen-reactive CD8⁺ T cells in pancreatic islets from deceased type 1 diabetes patients.

A direct association of islet-autoreactive T cells with β cell destruction in human pancreatic islets from type 1 diabetes (T1D) patients has never been demonstrated, and little is known about disease progression after diagnosis. Frozen pancreas samples were obtained from 45 cadaveric T1D donors with disease durations ranging from 1 wk to >50 yr, 14 nondiabetic controls, 5 nondiabetics with islet autoantibodies, 2 cases of gestational diabetes, and 6 T2D patients. Sections were systematically analyzed for the presence of insulin-sufficient β cells, CD8⁺ insulitic lesions, and HLA class I hyperexpression. Finally, consecutive sections from HLA-A2–expressing individuals were probed for CD8 T cell reactivity against six defined islet autoantigens associated with T1D by in situ tetramer staining. Both single and multiple CD8 T cell autoreactivities were detected within individual islets in a subset of patients up to 8 yr after clinical diagnosis. Pathological features such as HLA class I hyperexpression and insulitis were specific for T1D and persisted in a small portion of the patients with longstanding disease. Insulitic lesions consistently presented in a multifocal pattern with varying degrees of infiltration and β cell loss across affected organs. Our observations provide the first direct proof for islet autoreactivity within human islets and underscore the heterogeneous and chronic disease course.

Intravital imaging of CTLs killing islet cells in diabetic mice

Type 1 diabetes (T1D) is caused by autoimmune destruction of the insulin-producing β cells in the pancreatic islets, which are essentially mini-organs embedded in exocrine tissue. CTLs are considered to have a predominant role in the autoimmune destruction underlying T1D. Visualization of CTL-mediated killing of β cells would provide new insight into the pathogenesis of T1D, but has been technically challenging to achieve. Here, we report our use of intravital 2-photon imaging in mice to visualize the dynamic behavior of a virally expanded, diabetogenic CTL population in the pancreas at cellular resolution. Following vascular arrest and extravasation, CTLs adopted a random motility pattern throughout the compact exocrine tissue and displayed unimpeded yet nonlinear migration between anatomically nearby islets. Upon antigen encounter within islets, a confined motility pattern was acquired that allowed the CTLs to scan the target cell surface. A minority of infiltrating CTLs subsequently arrested at the β cell junction, while duration of stable CTL-target cell contact was on the order of hours. Slow-rate killing occurred in the sustained local presence of substantial numbers of effector cells. Collectively, these data portray the kinetics of CTL homing to and between antigenic target sites as a stochastic process at the sub-organ level and argue against a dominant influence of chemotactic gradients.

Incidental CD8 T cell reactivity against caspase-cleaved apoptotic self-antigens from ubiquitously expressed proteins in islets from prediabetic human leucocyte antigen-A2 transgenic non-obese diabetic mice

Apoptosis is known as a major mechanism which contributes to beta cell decay in type 1 diabetes. Commitment to this pathway generally involves caspase-mediated protein cleavage and was found to induce cross-presentation of a specific antigen repertoire under certain inflammatory conditions. We aimed to assess the significance of the CD8 T cell population reactive against such caspase-cleaved apoptotic self-antigens in pancreatic islets of prediabetic human leucocyte antigen (HLA)-A2 transgenic non-obese diabetic chimeric monochain transgene construct (NOD.HHD) mice. We have reproduced a unique peptide library consisting of human CD8 T cell-derived apoptosis-specific antigens, all of which belong to structural proteins expressed ubiquitously in human islets. Pancreatic islets from prediabetic NOD.HHD mice, harbouring humanized major histocompatibilty complex (MHC) class I, were isolated and handpicked at various ages, and islet-infiltrating CD8 T cells were expanded in vitro and used as responders in an interferon (IFN)-γ enzyme-linked immunospot (ELISPOT) assay. Human T2 cells were used as antigen-presenting cells (APC) to avoid endogenous antigen presentation. Analogous to the interindividual variability found with peptides from known islet autoantigens such as islet-specific glucose-6-phosphatase catalytic subunit related protein (IGRP) and insulin, some mice showed variable, low-degree CD8 T cell reactivity against caspase-cleaved self-antigens. Because reactivity was predominantly minor and often undetectable, we conclude that beta cell apoptosis does not routinely provoke the development of dominant cytotoxic T lymphocyte (CTL) reactive against caspase-cleaved self-antigens in the NOD.HHD model.

Protection against or triggering of Type 1 diabetes? Different roles for viral infections

The emergence of autoreactivity that ultimately destroys insulin-producing β-cells and causes Type 1 diabetes (T1D) is a result of genetic susceptibility and environmental factors, such as viral infections. The ability to induce strong cellular immune responses and to cause inflammation in the target organ makes viral infections prime candidates for the initiation of islet autoreactivity. Indeed, certain viruses have been linked to the occurrence of T1D based on epidemiological, serological and histological findings; and several rodent studies clearly demonstrate that viral infections can trigger autoimmunity. However, viruses have also been shown to efficiently prevent autoimmunity, which underlines the beneficial aspects of exposure to microbial agents as suggested by the hygiene hypothesis. Here, we will try to untangle some aspects of the complex interplay between viruses and the immune system and we will recapitulate by what rationale certain viruses have been associated with T1D.

Genetic vaccination for re-establishing T-cell tolerance in type 1 diabetes

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease resulting in the destruction of the insulin-secreting β cells. Currently, there is no established clinical approach to effectively suppress long-term the diabetogenic response. Genetic-based vaccination offers a general strategy to reestablish β-cell specific tolerance within the T-cell compartment. The transfer of genes encoding β-cell autoantigens, anti-inflammatory cytokines and/or immunomodulatory proteins has proven to be effective at preventing and suppressing the diabetogenic response in animal models of T1D. The current review will discuss genetic approaches to prevent and treat T1D with an emphasis on plasmid DNA- and adeno-associated virus-based vaccines.

Type 1 Diabetes: Etiology, Immunology, and Therapeutic Strategies

Type 1 diabetes (T1D) is a chronic autoimmune disease in which destruction or damaging of the beta-cells in the islets of Langerhans results in insulin deficiency and hyperglycemia. We only know for sure that autoimmunity is the predominant effector mechanism of T1D, but may not be its primary cause. T1D precipitates in genetically susceptible individuals, very likely as a result of an environmental trigger. Current genetic data point towards the following genes as susceptibility genes: HLA, insulin, PTPN22, IL2Ra, and CTLA4. Epidemiological and other studies suggest a triggering role for enteroviruses, while other microorganisms might provide protection. Efficacious prevention of T1D will require detection of the earliest events in the process. So far, autoantibodies are most widely used as serum biomarker, but T-cell readouts and metabolome studies might strengthen and bring forward diagnosis. Current preventive clinical trials mostly focus on environmental triggers. Therapeutic trials test the efficacy of antigen-specific and antigen-nonspecific immune interventions, but also include restoration of the affected beta-cell mass by islet transplantation, neogenesis and regeneration, and combinations thereof. In this comprehensive review, we explain the genetic, environmental, and immunological data underlying the prevention and intervention strategies to constrain T1D.

A novel technique for the in vivo imaging of autoimmune diabetes development in the pancreas by two-photon microscopy

Type 1 diabetes (T1D) is characterized by the immune-mediated destruction of beta cells in the pancreas. Little is known about the in vivo dynamic interactions between T cells and beta cells or the kinetic behavior of other immune cell subsets in the pancreatic islets. Utilizing multiphoton microscopy we have designed a technique that allows for the real-time visualization of diabetogenic T cells and dendritic cells in pancreatic islets in a live animal, including their interplay with beta cells and the vasculature. Using a custom designed stage, the pancreas was surgically exposed under live conditions so that imaging of islets under intact blood pressure and oxygen supply became possible. We demonstrate here that this approach allows for the tracking of diabetogenic leukocytes as well as vascularization phenotype of islets and accumulation of dendritic cells in islets during diabetes pathogenesis. This technique should be useful in mapping crucial kinetic events in T1D pathogenesis and in testing the impact of immune based interventions on T cell migration, extravasation and islet destruction.

Pathogenesis of type 1 diabetes mellitus: interplay between enterovirus and host

Enteroviruses are believed to contribute to the pathogenesis of type 1 diabetes mellitus (T1DM). In this Review, the interplay between infection with enteroviruses, the immune system and host genes is discussed. Data from retrospective and prospective epidemiological studies strongly suggest the involvement of enteroviruses, such as coxsackievirus B, in the development of T1DM. Enteroviral RNA and/or proteins can be detected in tissues of patients with T1DM. Isolation of coxsackievirus B4 from the pancreas of patients with T1DM or the presence of enteroviral components in their islets strengthens the hypothesis of a relationship between the virus and the disease. Enteroviruses can play a part in the early phase of T1DM through the infection of beta cells and the activation of innate immunity and inflammation. In contrast with its antiviral role, virus-induced interferon alpha can be deleterious, acting as an initiator of the autoimmunity directed against beta cells. Enteroviruses, through persistent and/or successive infections, can interact with the adaptive immune system. Host genes, such as IFIH1, that influence susceptibility to T1DM are associated with antiviral activities. An increased activity of the IFIH1 protein may promote the development of T1DM. An improved knowledge of the pathogenic mechanisms of enterovirus infections should help to uncover preventive strategies for T1DM.

Breakthrough in diabetes therapy ... Just around the corner?

Inspired by the articles presented in this issue of The Review of Diabetic Studies, we considered it useful to summarize the latest achievements and current challenges we face in the search for a cure of type 1 diabetes. In this editorial article, we took into account how the research landscape has changed in only a few years. While modern lifestyles impose new concerns, now we have a better knowledge of the various aspects of the disease that can be used to treat our young patients with more appropriate approaches, thereby eliminating old and obsolete prejudices.

The role of the CXCL10/CXCR3 system in type 1 diabetes

Despite intervention with insulin, type 1 diabetes gradually deteriorates the patients' quality of life. The disease is characterized by an immune-mediated destruction of pancreatic beta-cells. Its etiology, however, remains controversial. Some studies argue that glutamic acid decarboxylase (GAD) antigen and GAD-reactive T cells are critical players in the development of diabetes by affecting the Th cell balance. A T-helper 1 (Th1)-dominant immune response is considered to be important in beta-cell failure in both human and animal models of type 1 diabetes. The Th1-type chemokine, CXCL10, and its receptor, CXCR3, are involved not only in the immune response, but also in the suppression of beta-cell proliferation. Thus, understanding the CXCL10/CXCR3 system may be important for finding a cure. In this short review, we discuss the role of the CXCL10/CXCR3 system in type 1 diabetes and propose relevant treatment options.