Balasubramanian Krishnamurthy

Responses against islet antigens in NOD mice are prevented by tolerance to proinsulin but not IGRP

Type 1 diabetes (T1D) is characterized by immune responses against several autoantigens expressed in pancreatic beta cells. T cells specific for proinsulin and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) can induce T1D in NOD mice. However, whether immune responses to multiple autoantigens are caused by spreading from one to another or whether they develop independently of each other is unknown. As cytotoxic T cells specific for IGRP were not detected in transgenic NOD mice tolerant to proinsulin, we determined that immune responses against proinsulin are necessary for IGRP-specific T cells to develop. On the other hand, transgenic overexpression of IGRP resulted in loss of intra-islet IGRP-specific T cells but did not protect NOD mice from insulitis or T1D, providing direct evidence that the response against IGRP is downstream of the response to proinsulin. Our results suggest that pathogenic proinsulin-specific immunity in NOD mice subsequently spreads to other antigens such as IGRP.

Gut microbial metabolites limit the frequency of autoimmune T cells and protect against type 1 diabetes

Gut dysbiosis might underlie the pathogenesis of type 1 diabetes. In mice of the non-obese diabetic (NOD) strain, we found that key features of disease correlated inversely with blood and fecal concentrations of the microbial metabolites acetate and butyrate. We therefore fed NOD mice specialized diets designed to release large amounts of acetate or butyrate after bacterial fermentation in the colon. Each diet provided a high degree of protection from diabetes, even when administered after breakdown of immunotolerance. Feeding mice a combined acetate- and butyrate-yielding diet provided complete protection, which suggested that acetate and butyrate might operate through distinct mechanisms. Acetate markedly decreased the frequency of autoreactive T cells in lymphoid tissues, through effects on B cells and their ability to expand populations of autoreactive T cells. A diet containing butyrate boosted the number and function of regulatory T cells, whereas acetate- and butyrate-yielding diets enhanced gut integrity and decreased serum concentration of diabetogenic cytokines such as IL-21. Medicinal foods or metabolites might represent an effective and natural approach for countering the numerous immunological defects that contribute to T cell–dependent autoimmune diseases.

Autoimmunity to Both Proinsulin and IGRP Is Required for Diabetes in Nonobese Diabetic 8.3 TCR Transgenic Mice

T cells specific for proinsulin and islet-specific glucose-6-phosphatase catalytic subunit related protein (IGRP) induce diabetes in nonobese diabetic (NOD) mice. TCR transgenic mice with CD8+ T cells specific for IGRP206–214 (NOD8.3 mice) develop accelerated diabetes that requires CD4+ T cell help. We previously showed that immune responses against proinsulin are necessary for IGRP206–214-specific CD8+ T cells to expand. In this study, we show that diabetes development is dramatically reduced in NOD8.3 mice crossed to NOD mice tolerant to proinsulin (NOD-PI mice). This indicates that immunity to proinsulin is even required in the great majority of NOD8.3 mice that have a pre-existing repertoire of IGRP206–214-specific cells. However, protection from diabetes could be overcome by inducing islet inflammation either by a single dose of streptozotocin or anti-CD40 agonist Ab treatment. This suggests that islet inflammation can substitute for proinsulin-specific CD4+ T cell help to activate IGRP206–214-specific T cells.

NF-κB in Type 1 Diabetes

Type 1 diabetes is an autoimmune disease in which pancreatic beta cells are destroyed by autoreactive T cells. It is a common pediatric disease with increasing incidence. Islet transplantation may be a therapeutic option, however, the current limitations of this procedure mean that for most sufferers of type 1 diabetes there is no cure. The transcription factor NF-κB has been widely studied for its role in development of type 1 diabetes. Recent data have shown that NF-κB is required for activation of autoreactive T cells, and its hyperactivity in monocytes and dendritic cells results in altered cytokine secretion and antigen presentation, which ultimately contributes to the initiation of type 1 diabetes. NF-κB is also activated by a number of proinflammatory cytokines to regulate both the survival and death of beta cells. The critical role of NF-κB in type 1 diabetes renders it a promising pharmaceutical target in the intervention of this disease and further understanding of the NF-κB pathway will have an important implication on the development of novel and safe therapeutic strategies.

TNF Receptor 1 Deficiency Increases Regulatory T Cell Function in Nonobese Diabetic mice

TNF has been implicated in the pathogenesis of type 1 diabetes. When administered early in life, TNF accelerates and increases diabetes in NOD mice. However, when administered late, TNF decreases diabetes incidence and delays onset. TNFR1-deficient NOD mice were fully protected from diabetes and only showed mild peri-insulitis. To further dissect how TNFR1 deficiency affects type 1 diabetes, these mice were crossed to β cell-specific, highly diabetogenic TCR transgenic I-Ag7–restricted NOD4.1 mice and Kd-restricted NOD8.3 mice. TNFR1-deficient NOD4.1 and NOD8.3 mice were protected from diabetes and had significantly less insulitis compared with wild type NOD4.1 and NOD8.3 controls. Diabetic NOD4.1 mice rejected TNFR1-deficient islet grafts as efficiently as control islets, confirming that TNFR1 signaling is not directly required for β cell destruction. Flow cytometric analysis showed a significant increase in the number of CD4+CD25+Foxp3+ T regulatory cells in TNFR1-deficient mice. TNFR1-deficient T regulatory cells were functionally better at suppressing effector cells than were wild type T regulatory cells both in vitro and in vivo. This study suggests that blocking TNF signaling may be beneficial in increasing the function of T regulatory cells and suppression of type 1 diabetes.

Autoreactive Cytotoxic T Lymphocytes Acquire Higher Expression of Cytotoxic Effector Markers in the Islets of NOD Mice after Priming in Pancreatic Lymph Nodes

Cytotoxic T lymphocytes (CTLs) that cause type 1 diabetes are activated in draining lymph nodes and become concentrated as fully active CTLs in inflamed pancreatic islets. It is unclear whether CTL function is driven by signals received in the lymph node or also in the inflamed tissue. We studied whether the development of cytotoxicity requires further activation in islets. Autoreactive CTLs found in the islets of diabetes-prone NOD mice had acquired much higher expression of the cytotoxic effector markers granzyme B, interferon γ, and CD107a than had those in the pancreatic lymph node (PLN). Increased expression seemed to result from stimulation in the islet itself. T cells held up from migrating from the PLN by administration of the sphingosine-1-phosphate agonist FTY720 did not increase expression of cytotoxic molecules in the PLN. Stimulation did not require antigen presentation or cytokine secretion by the target β cells because it was not affected by the absence of class I major histocompatibility complex expression or by the overexpression of suppressor of cytokine signaling-1. Activation of CD40-expressing cells stimulated increased CTL function and β-cell destruction, suggesting that signals derived from CD40-expressing cells promote the acquisition of cytotoxicity in the islet environment. These data provide in vivo evidence that stimulation of cytotoxic effector molecule expression occurs in inflamed islets and is independent of β cells.

Perinatal tolerance to proinsulin is sufficient to prevent autoimmune diabetes

High-affinity self-reactive thymocytes are purged in the thymus, and residual self-reactive T cells, which are detectable in healthy subjects, are controlled by peripheral tolerance mechanisms. Breakdown in these mechanisms results in autoimmune disease, but antigen-specific therapy to augment natural mechanisms can prevent this. We aimed to determine when antigen-specific therapy is most effective. Islet autoantigens, proinsulin (PI), and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) were expressed in the antigen-presenting cells (APCs) of autoimmune diabetes-prone nonobese diabetic (NOD) mice in a temporally controlled manner. PI expression from gestation until weaning was sufficient to completely protect NOD mice from diabetes, insulitis, and development of insulin autoantibodies. Insulin-specific T cells were significantly diminished, were naive, and did not express IFN-γ when challenged. This long-lasting effect from a brief period of treatment suggests that autoreactive T cells are not produced subsequently. We tracked IGRP206-214-specific CD8+ T cells in NOD mice expressing IGRP in APCs. When IGRP was expressed only until weaning, IGRP206-214-specific CD8+ T cells were not detected later in life. Thus, anti-islet autoimmunity is determined during early life, and autoreactive T cells are not generated in later life. Bolstering tolerance to islet antigens in the perinatal period is sufficient to impart lasting protection from diabetes.

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.

Intra‐islet proliferation of cytotoxic T lymphocytes contributes to insulitis progression

Infiltration of pancreatic islets by immune cells, termed insulitis, increases progressively once it begins and leads to clinical type 1 diabetes. But even after diagnosis some islets remain unaffected and infiltration is patchy rather than uniform. Traffic of autoreactive T cells into the pancreas is likely to contribute to insulitis progression but it could also depend on T‐cell proliferation within islets. This study utilizes transgenic NOD mice to assess the relative contributions of these two mechanisms. Progression of insulitis in NOD8.3 TCR transgenic mice was mildly reduced by inhibition of T‐cell migration with the drug FTY720. In FTY720‐treated mice, reduced beta cell MHC class I expression prevented progression of insulitis both within affected islets and to previously unaffected islets. CTL proliferation was significantly reduced in islets with reduced or absent beta cell expression of MHC class I protein. This indicates that intra‐islet proliferation, apparently dependent on beta cell antigen presentation, in addition to recruitment, is a significant factor in progression of insulitis.

An Algorithm Guiding Patient Responses to Real-Time-Continuous Glucose Monitoring Improves Quality of Life

OBJECTIVE This study evaluated the impact on quality of life (QoL) of an algorithm guiding the responses of continuous subcutaneous insulin infusion (CSII)-treated type 1 diabetes (T1D) patients using real-time (RT)-continuous glucose monitoring (CGM). RESEARCH DESIGN AND METHODS Sixty CSII-treated T1D participants (13-70 years old, glycosylated hemoglobin [HbA1c] ≤ 9.5%), including adult and adolescent subgroups, were randomized in age-, gender-, and HbA1c-matched pairs. Phase 1 was an open 16-week multicenter randomized controlled trial; Group A received CSII/RT-CGM with the algorithm, and Group B received CSII/RT-CGM without algorithm. Phase 2 was the 16-32-week follow-up study; Group A returned to usual care (CSII without RT-CGM), and Group B was provided with algorithm at 16 weeks. QoL was assessed by DQOL (adults) and DQOLY (adolescents) questionnaires at baseline, 16 weeks, and 32 weeks. Higher scores (range 1-5) indicate poorer QoL. Analysis was by analysis of variance (between group for baseline-16 weeks) and paired two-tailed t tests (within group for baseline and 32 weeks) with significance at P < 0.05. RESULTS Withdrawals left 28 of 30 patients in Group A and 27 of 30 patients in Group B at 32 weeks. In Phase 1, QoL in Group A (2.16 [0.44] baseline to 1.86 [0.40] at 16 weeks) improved compared with Group B (2.03 [0.47] to 2.03 [0.50]) (P = 0.002). Change in QoL correlated with changes in HbA1c (R = 0.36; P = 0.007). In Phase 2, Group A QoL was better at 32 weeks compared with baseline (2.16 [0.44] vs. 2.02 [0.43]) (P = 0.04) but was not in Group B (2.03 [0.47] vs. 1.99 [0.51]) (P = not significant). CONCLUSIONS An algorithm guiding CSII-treated T1D responses to RT-CGM improved QoL, which persisted post-RT-CGM withdrawal. Algorithm provision at RT-CGM initiation was required to benefit QoL.