Islet Autoimmunity In Type Research Articles

Prioritization of infectious epitopes for translational investigation in type 1 diabetes etiology

Molecular mimicry is one mechanism by which infectious agents are thought to trigger islet autoimmunity in type 1 diabetes. With a growing number of reported infectious agents and islet antigens, strategies to prioritize the study of infectious agents are critically needed to expedite translational research into the etiology of type 1 diabetes. In this work, we developed an in-silico pipeline for assessing molecular mimicry in type 1 diabetes etiology based on sequence homology, empirical binding affinity to specific MHC molecules, and empirical potential for T-cell immunogenicity. We then assess whether potential molecular mimics were conserved across other pathogens known to infect humans. Overall, we identified 61 potentially high-impact molecular mimics showing sequence homology, strong empirical binding affinity, and empirical immunogenicity linked with specific MHC molecules. We further found that peptide sequences from 32 of these potential molecular mimics were conserved across several human pathogens. These findings facilitate translational evaluation of molecular mimicry in type 1 diabetes etiology by providing a curated and prioritized list of peptides from infectious agents for etiopathologic investigation. These results may also provide evidence for generation of infectious and HLA-specific preclinical models and inform future screening and preventative efforts in genetically susceptible populations.

Pancreas-Brain Crosstalk.

The neural regulation of glucose homeostasis in normal and challenged conditions involves the modulation of pancreatic islet-cell function. Compromising the pancreas innervation causes islet autoimmunity in type 1 diabetes and islet cell dysfunction in type 2 diabetes. However, despite the richly innervated nature of the pancreas, islet innervation remains ill-defined. Here, we review the neuroanatomical and humoral basis of the cross-talk between the endocrine pancreas and autonomic and sensory neurons. Identifying the neurocircuitry and neurochemistry of the neuro-insular network would provide clues to neuromodulation-based approaches for the prevention and treatment of diabetes and obesity.

Emerging Therapeutic Strategies to Restore Regulatory T Cell Control of Islet Autoimmunity in Type 1 Diabetes

Despite many decades of investigation uncovering the autoimmune mechanisms underlying Type 1 Diabetes (T1D), translating these findings into effective therapeutics has proven extremely challenging. T1D is caused by autoreactive T cells that become inappropriately activated and kill the β cells in the pancreas, resulting in insulin insufficiency and hyperglycemia. A large body of evidence supports the idea that the unchecked activation and expansion of autoreactive T cells in T1D is due to defects in immunosuppressive regulatory T cells (Tregs) that are critical for maintaining peripheral tolerance to islet autoantigens. Hence, repairing these Treg deficiencies is a much sought-after strategy to treat the disease. To accomplish this goal in the most precise, effective and safest way possible, restored Treg functions will need to be targeted towards suppressing the autoantigen-specific immune responses only and/or be localized in the pancreas. Here we review the most recent developments in designing Treg therapies that go beyond broad activation or expansion of non-specific polyclonal Treg populations. We focus on two cutting-edge strategies namely ex vivo generation of optimized Tregs for re-introduction in T1D patients vs direct in situ stimulation and restoration of endogenous Treg function.

Investigating the potential impact of post translational modification of auto-antigens by tissue transglutaminase on humoral islet autoimmunity in type 1 diabetes

BackgroundPost-translational modification (PTM) of antigens plays a role in the pathogenesis of many autoimmune disorders. In coeliac disease (CD), tissue transglutaminase (tTG) deamidates gliadin peptides to activate the immune response against the gut endomysium. CD is six times more prevalent in type 1 diabetes (T1D) patients than in the general population. HypothesistTG also modifies auto-antigens implicated in the pathogenesis of T1D, leading to an autoimmune response to pancreatic β-cells. MethodstTG PTM was investigated in the following auto-antigens, which had been previously shown to have high importance in the development of T1D: glutamic acid decarboxylase isoform 65 (GAD65), full length islet antigen (IA-2), intracellular portion of IA-2 (IA-2ic), and both isoforms of zinc transporter 8 (ZnT8W and ZnT8R), on antibody binding. Radiolabelled antigen was incubated with tTG for 20 h at 37 °C in 100 mM Denver buffer, 3.33 nM CaCl2, at pH 7.3. Antibody binding in 20 mixed samples from the Bart’s-Oxford (BOX) cohort was measured by radiobinding assay. ResultsResults varied between serum samples. Generally, tTG treatment of ZnT8W, ZnT8R and IA-2ic showed no significant change in antigen: autoantibody binding, while increases in binding were observed with tTG-treated GAD65 and full length IA-2. ConclusionIn the case of GAD65, full length IA-2, the strength of antibody: antigen binding increased after incubation with tTG. However, the exact tTG-modification events that occurred requires further elucidation.

Setting the Stage for Islet Autoimmunity in Type 2 Diabetes: Obesity-Associated Chronic Systemic Inflammation and Endoplasmic Reticulum (ER) Stress.

Islet autoimmunity has been identified as a component of both type 1 (T1D) and type 2 (T2D) diabetes, but the pathway through which islet autoimmunity develops in T1D and T2D may be different. Acknowledging the presence of islet autoimmunity in the pathophysiology of T2D, a historically nonautoimmune metabolic disease, would pave the way for important changes in classifications of and therapeutic options for T2D. In order to fully appreciate the importance of islet autoimmunity in T2D, the underlying mechanisms for immune system activation need to be explored. In this review, we focus on the potential origin of immune system activation (innate and adaptive) leading to the development of islet autoimmunity in T2D.

Vaccinations in early life are not associated with development of islet autoimmunity in type 1 diabetes high-risk children: Results from prospective cohort data

Aims/hypothesisVaccinations in early childhood potentially stimulate the immune system and may thus be relevant for the pathogenesis of autoimmune diseases such as type 1 diabetes (T1D). We determined the association of vaccination burden with T1D-associated islet autoimmunity in children with high familial risk followed prospectively from birth. MethodsA total of 20,570 certified vaccination records from 1918 children were correlated with time to onset of T1D-associated islet autoimmunity using Cox regression, considering multiple time periods up until age two years and vaccination types, and adjusting for HLA genotype, sex, delivery mode, season of birth, preterm delivery and maternal T1D status. Additionally, prospective claims data of 295,420 subjects were used to validate associations for the tick-borne encephalitis (TBE) vaccination. ResultsMost vaccinations were not associated with a significantly increased hazard ratio (HR) for islet autoimmunity (e.g. HR [95% confidence interval]: 1.08 [0.96–1.21] per additional vaccination against measles, mumps and rubella at age 0–24months). TBE vaccinations within the first two years of life were nominally associated with a significantly increased autoimmunity risk (HR: 1.44 [1.06–1.96] per additional vaccination at age 0–24months), but this could not be confirmed with respect to outcome T1D in the validation cohort (HR: 1.02 [0.90–1.16]). ConclusionsWe found no evidence that early vaccinations increase the risk of T1D-associated islet autoimmunity development. The potential association with early TBE vaccinations could not be confirmed in an independent cohort and appears to be a false positive finding.

Evaluation of the fidelity of immunolabelling obtained with clone 5D8/1, a monoclonal antibody directed against the enteroviral capsid protein, VP1, in human pancreas

Enteroviral infection has been implicated in the development of islet autoimmunity in type 1 diabetes and enteroviral antigen expression has been detected by immunohistochemistry in the pancreatic beta cells of patients with recent-onset type 1 diabetes. However, the immunohistochemical evidence relies heavily on the use of a monoclonal antibody, clone 5D8/1, raised against an enteroviral capsid protein, VP1. Recent data suggest that the clone 5D8/1 may also recognise non-viral antigens; in particular, a component of the mitochondrial ATP synthase (ATP5B) and an isoform of creatine kinase (CKB). Therefore, we evaluated the fidelity of immunolabelling by clone 5D8/1 in the islets of patients with type 1 diabetes. Enteroviral VP1, CKB and ATP5B expression were analysed by western blotting, RT-PCR and immunocytochemistry in a range of cultured cell lines, isolated human islets and human tissue. Clone 5D8/1 labelled CKB, but not ATP5B, on western blots performed under denaturing conditions. In cultured human cell lines, isolated human islets and pancreas sections from patients with type 1 diabetes, the immunolabelling of ATP5B, CKB and VP1 by 5D8/1 was readily distinguishable. Moreover, in a human tissue microarray displaying more than 80 different cells and tissues, only two (stomach and colon; both of which are potential sites of enterovirus infection) were immunopositive when stained with clone 5D8/1. When used under carefully optimised conditions, the immunolabelling pattern detected in sections of human pancreas with clone 5D8/1 did not reflect cross-reactivity with either ATP5B or CKB. Rather, 5D8/1 is likely to be representative of enteroviral antigen expression.

Hepatic Steatosis in Type 1 Diabetes

Islet autoimmunity in type 1 diabetes results in the loss of the pancreatic β-cells. The consequences of insulin deficiency in the portal vein for liver fat are poorly understood. Under normal conditions, the portal vein provides 75% of the liver blood supply. Recent studies suggest that non-alcoholic fatty liver disease (NAFLD) may be more common in type 1 diabetes than previously thought, and may serve as an independent risk marker for some chronic diabetic complications. The pathogenesis of NAFLD remains obscure, but it has been hypothesized that hepatic fat accumulation in type 1 diabetes may be due to lipoprotein abnormalities, hyperglycemia-induced activation of the transcription factors carbohydrate response element-binding protein (ChREBP) and sterol regulatory element-binding protein 1c (SREBP-1c), upregulation of glucose transporter 2 (GLUT2) with subsequent intrahepatic fat synthesis, or a combination of these mechanisms. Novel approaches to non-invasive determinations of liver fat may clarify the consequences for liver metabolism when the pancreas has ceased producing insulin. This article aims to review the factors potentially contributing to hepatic steatosis in type 1 diabetes, and to assess the feasibility of using liver fat as a prognostic and/or diagnostic marker for the disease. It provides a background and a case for possible future studies in the field.

Identification of Autoantibody-Negative Autoimmune Type 2 Diabetic Patients

OBJECTIVEIslet autoimmunity has long been recognized in the pathogenesis of type 1 diabetes and is becoming increasingly acknowledged as a component in the pathogenesis of type 2 diabetes. Islet reactive T cells and autoantibodies have been demonstrated in type 1 diabetes, whereas islet autoimmunity in type 2 diabetes has been limited to islet autoantibodies. In this study, we investigated whether islet reactive T cells might also be present in type 2 diabetic patients and how islet reactive T cells correlate with β-cell function.RESEARCH DESIGN AND METHODSAdult phenotypic type 2 diabetic patients (n = 36) were screened for islet reactive T-cell responses using cellular immunoblotting and five islet autoantibodies (islet cell antibody, GADA, insulin autoantibody, insulinoma-associated protein-2 autoantibody, and zinc transporter autoantibody).RESULTSWe identified four subgroups of adult phenotypic type 2 diabetic patients based on their immunological status (Ab−T−, Ab+T−, Ab−T+, and Ab+T+). The Ab−T+ type 2 diabetic patients demonstrated T-cell responses similar to those of the Ab+T+ type 2 diabetic patients. Data were adjusted for BMI, insulin resistance, and duration of diabetes. Significant differences (P < 0.02) were observed among groups for fasting and glucagon-stimulated C-peptide responses. T-cell responses to islet proteins were also demonstrated to fluctuate less than autoantibody responses.CONCLUSIONSWe have identified a group of adult autoimmune phenotypic type 2 diabetic patients who are Ab−T+ and thus would not be detected using autoantibody testing alone. We conclude that islet autoimmunity may be more prevalent in adult phenotypic type 2 diabetic patients than previously estimated.

Identification of Tyrosine Phosphatase 2(256–760) Construct as a New, Sensitive Marker for the Detection of Islet Autoimmunity in Type 2 Diabetic Patients

The presence of autoantibodies to islet antigens GAD and/or tyrosine phosphatase 2 (IA-2) in type 2 diabetic patients (latent autoimmune diabetes in adults [LADA]) identifies subjects at high risk to develop insulin dependency. The aim of this study was to dissect humoral anti-IA-2 immune response in Caucasian LADA patients, identifying the most sensitive construct to evaluate IA-2 immunoreactivity and comparing LADA IA-2 epitope specificities to those found in type 1 diabetes. We analyzed 177 LADA and 978 type 2 diabetic patients with different disease duration, collected in a nationwide Italian survey, the Non-Insulin Requiring Autoimmune Diabetes (NIRAD) study aimed at assessing prevalence and characteristics of autoimmune diabetes in type 2 diabetic patients and 106 newly diagnosed type 1 diabetic patients (53 children, 53 adults). By radioimmunoassay, we analyzed humoral immunoreactivity to seven IA-2 constructs: IA-2(PTP (687-979)), IA-2((761-964)), IA-2((256-760)), IA-2(JM (601-630)), IA-2(IC (605-979)), IA-2(BDC (256-556:630-979)), and IA-2(FL (1-979)). IA-2((256-760)) fragment was identified as the marker with the highest sensitivity for detection of humoral IA-2 immunoreactivity in LADA patients, identifying IA-2 autoantibodies in approximately 30% of GAD antibody (GADA)-positive LADA patients and in 3.4% of GADA-negative type 2 diabetic patients. LADA IA-2((256-760))A positivity was associated with an increased frequency of autoimmune diabetes HLA-susceptible genotypes and with a higher risk for developing thyroid autoimmunity compared with autoantibody-negative type 2 diabetic patients. At disease diagnosis, adult-onset type 1 diabetic and LADA patients showed a lower IA-2 COOH-terminal immunoreactivity compared with childhood-onset type 1 diabetic patients. IA-2 immunoreactivity in LADA patients has thus far been underestimated, and IA-2((256-760)) autoantibody detection may represent a novel diagnostic tool for the identification of islet autoimmunity in these patients.

IA-2 autoantibodies in incident type I diabetes patients are associated with a polyadenylation signal polymorphism in GIMAP5

In a large case-control study of Swedish incident type I diabetes patients and controls, 0-34 years of age, we tested the hypothesis that the GIMAP5 gene, a key genetic factor for lymphopenia in spontaneous BioBreeding rat diabetes, is associated with type I diabetes; with islet autoantibodies in incident type I diabetes patients or with age at clinical onset in incident type I diabetes patients. Initial scans of allelic association were followed by more detailed logistic regression modeling that adjusted for known type I diabetes risk factors and potential confounding variables. The single nucleotide polymorphism (SNP) rs6598, located in a polyadenylation signal of GIMAP5, was associated with the presence of significant levels of IA-2 autoantibodies in the type I diabetes patients. Patients with the minor allele A of rs6598 had an increased prevalence of IA-2 autoantibody levels compared to patients without the minor allele (OR=2.2; Bonferroni-corrected P=0.003), after adjusting for age at clinical onset (P=8.0 x 10(-13)) and the numbers of HLA-DQ A1*0501-B1*0201 haplotypes (P=2.4 x 10(-5)) and DQ A1*0301-B1*0302 haplotypes (P=0.002). GIMAP5 polymorphism was not associated with type I diabetes or with GAD65 or insulin autoantibodies, ICA, or age at clinical onset in patients. These data suggest that the GIMAP5 gene is associated with islet autoimmunity in type I diabetes and add to recent findings implicating the same SNP in another autoimmune disease.

T-Cell Epitopes in Type 1 Diabetes Autoantigen Tyrosine Phosphatase IA-2: Potential for Mimicry with Rotavirus and Other Environmental Agents

The tyrosine phosphatase IA-2 is a molecular target of pancreatic islet autoimmunity in type 1 diabetes. T-cell epitope peptides in autoantigens have potential diagnostic and therapeutic applications, and they may hold clues to environmental agents with similar sequences that could trigger or exacerbate autoimmune disease. We identified 13 epitope peptides in IA-2 by measuring peripheral blood T-cell proliferation to 68 overlapping, synthetic peptides encompassing the intracytoplasmic domain of IA-2 in six at-risk type 1 diabetes relatives selected for HLA susceptibility haplotypes. The dominant epitope, VIVMLTPLVEDGVKQC (aa 805-820), which elicited the highest T-cell responses in all at-risk relatives, has 56% identity and 100% similarity over 9 amino acids (aa) with a sequence in VP7, a major immunogenic protein of human rotavirus. Both peptides bind to HLA-DR4(*0401) and are deduced to present identical aa to the T-cell receptor. The contiguous sequence of VP7 has 75% identity and 92% similarity over 12 aa with a known T-cell epitope in glutamic acid decarboxylase (GAD), another autoantigen in type 1 diabetes. This dominant IA-2 epitope peptide also has 75-45% identity and 88-64% similarity over 8-14 aa to sequences in Dengue, cytomegalovirus, measles, hepatitis C, and canine distemper viruses, and the bacterium Haemophilus influenzae. Three other IA-2 epitope peptides are 71-100% similar over 7-12 aa to herpes, rhino-, hanta- and flaviviruses. Two others are 80-82% similar over 10-11 aa to sequences in milk, wheat, and bean proteins. Further studies should now be carried out to directly test the hypothesis that T-cell activation by rotavirus and possibly other viruses, and dietary proteins, could trigger or exacerbate beta-cell autoimmunity through molecular mimicry with IA-2 and (for rotavirus) GAD.