Stable activity of diabetogenic cells with age in NOD mice: dynamics of reconstitution and adoptive diabetes transfer in immunocompromised mice

Fatty acid binding protein 4 promotes autoimmune diabetes by recruitment and activation of pancreatic islet macrophages

Both innate and adaptive immune cells are critical players in autoimmune destruction of insulin-producing β cells in type 1 diabetes. However, the early pathogenic events triggering the recruitment and activation of innate immune cells in islets remain obscure. Here we show that circulating fatty acid binding protein 4 (FABP4) level was significantly elevated in patients with type 1 diabetes and their first-degree relatives and positively correlated with the titers of several islet autoantibodies. In nonobese diabetic (NOD) mice, increased FABP4 expression in islet macrophages started from the neonatal period, well before the occurrence of overt diabetes. Furthermore, the spontaneous development of autoimmune diabetes in NOD mice was markedly reduced by pharmacological inhibition or genetic ablation of FABP4 or adoptive transfer of FABP4-deficient bone marrow cells. Mechanistically, FABP4 activated innate immune responses in islets by enhancing the infiltration and polarization of macrophages to proinflammatory M1 subtype, thus creating an inflammatory milieu required for activation of diabetogenic CD8+ T cells and shift of CD4+ helper T cells toward Th1 subtypes. These findings demonstrate FABP4 as a possible early mediator for β cell autoimmunity by facilitating crosstalk between innate and adaptive immune cells, suggesting that pharmacological inhibition of FABP4 may represent a promising therapeutic strategy for autoimmune diabetes.

Mechanisms of diabetic autoimmunity: I--the inductive interface between islets and the immune system at onset of inflammation

The mechanisms of autoimmune reactivity onset in type 1 diabetes (T1D) remain elusive despite extensive experimentation and discussion. We reconsider several key aspects of the early stages of autoimmunity at four levels: islets, pancreatic lymph nodes, thymic function and peripheral immune homeostasis. Antigen presentation is the islets and has the capacity to provoke immune sensitization, either in the process of physiological neonatal β cell apoptosis or as a consequence of cytolytic activity of self-reactive thymocytes that escaped negative regulation. Diabetogenic effectors are efficiently expanded in both the islets and the lymph nodes under conditions of empty lymphoid niches during a period of time coinciding with a synchronized wave of β cell apoptosis surrounding weaning. A major drive of effector cell activation and expansion is inherent peripheral lymphopenia characteristic of neonates, though it remains unclear when is autoimmunity triggered in subjects displaying hyperglycemia in late adolescence. Our analysis suggests that T1D evolves through coordinated activity of multiple physiological mechanisms of stimulation within specific characteristics of the neonate immune system.

Mechanisms of diabetic autoimmunity: II--Is diabetes a central or peripheral disorder of effector and regulatory cells?

Two competing hypotheses aiming to explain the onset of autoimmune reactions are discussed in the context of genetic and environmental predisposition to type 1 diabetes (T1D). The first hypothesis has evolved along characterization of the mechanisms of self-discrimination and attributes diabetic autoimmunity to escape of reactive T cells from central regulation in the thymus. The second considers frequent occurrence of autoimmune reactions within the immune homunculus, which are adequately suppressed by regulatory T cells originating from the thymus, and occasionally, insufficient suppression results in autoimmunity. Besides thymic dysfunction, deregulation of both effector and suppressor cells can in fact result from homeostatic aberrations at the peripheral level during initial stages of evolution of adaptive immunity. Pathogenic cells sensitized in the islets are efficiently expanded in the target tissue and pancreatic lymph nodes of lymphopenic neonates. In parallel, the same mechanisms of peripheral sensitization contribute to tolerization through education of naïve/effector T cells and expansion of regulatory T cells. Experimental evidence presented for each individual mechanism implies that T1D may result from a primary effector or suppressor immune abnormality. Disturbed self-tolerance leading to T1D may well result from peripheral deregulation of innate and adaptive immunity, with variable contribution of central thymic dysfunction.

The influence of exendin-4 intervention on -obese diabetic mouse blood and the pancreatic tissue immune microenvironment

The aim of the study was to determine the influence of exendin-4 intervention on non-obese diabetic (NOD) mouse blood and the pancreatic tissue immune microenvironment. A total of 40 clean NOD mice were used in the study and randomly divided into 4 groups (n=10/group). The first group was blank control group D with normal saline intervention, and with different doses of exendin, i.e.,-4 2, 4 and 8 µg/kg/day. The three remaining groups were: i) Low-dose group A; ii) medium-dose group B; and iii) high-dose group C. Mice in the four groups went through intervention for 8 weeks. Their mass and blood glucose levels were tested each week. After 8 weeks, the mice were sacrificed, and mouse serum samples were reserved. The ELISA method was used to test peripheral blood (PB), IL-2, IFN-γ and IL-10 levels. Pancreatic samples were created. Immunohistochemistry was used to observe the infiltration degree of mouse pancreatitis and the local expression state of pancreatic IL-10. Mouse pancreatic tissues were suspended in pancreatic cell suspension. Flow cytometry was used to test the state of T-cell subsets CD4 and CD25. Mouse pancreatitis in control group D was mainly at grade 2and 3. Under a light microscope, it was observed that pancreatic cell morphology was in disorder, and the size and quantity of the pancreas was small. Mouse pancreatitis in the exendin-4 low-dose group A, medium-dose group B and high-dose group C was mainly at grade 0 and 1. Under a light microscope, it was observed that pancreatic cell morphology improved, the infiltration degree of lymphocyte was improved and pancreatic islet size was restored somewhat. Additionally, a few brownish granules were identified within the pancreatic sample cells in control group D. There were many brownish granules with deep color within the pancreatic sample cells in exendin-4 low-dose group A, medium-dose group B and high-dose group C. IL-10 immunohistochemistry scores in the low-dose group A, medium-dose group B and high-dose group C were 3.82±0.72, 4.34±0.86 and 4.81±0.94, respectively, and were higher than the score of 2.25±0.63 in control group D. CD4+CD25+T-cell proportions in mouse pancreatic tissues of low-dose group A, medium-dose group B and high-dose group C were 5.31, 5.53 and 5.74%, respectively, which were higher than that of the CD4+CD25+T-cell proportion (1.62% in control group D). The CD4+CD25^high T-cell proportion in CD4+T-cells in group A, B and C increased. Compared with control group D, serum IL-10 levels in the exendin-4 low-dose group A, medium-dose group B and high-dose group C increased (P<0.05), while levels of IL-2 and IFN-γ decreased (P<0.05). Additionally, the difference of serum IL-10, IL-2 and IFN-γ levels in the low-dose group A, medium-dose group B and high-dose group C was of statistical significance (P<0.05). Exendin-4 intervention can increase quantities of CD4 and CD8+T cells in NOD mouse pancreases, with PB IL-10 expression and local expression of IL-10 in pancreatic tissues. It also can inhibit the expression of serum IL-2 and IFN-γ, regulate the organism immune microenvironment and prevent diabetes. CD4+CD25^high T cells increase in NOD tumor infiltration lymphocytes mediated by exendin-4 intervention, which may be related to the fact that exendin-4 inhibits the lethal effect of CD8+T cells through contact among cells and eventually exerts immunosuppressive effect.

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.

RNase L contributes to experimentally induced type 1 diabetes onset in mice

The cause of type 1 diabetes continues to be a focus of investigation. Studies have revealed that interferon α (IFNα) in pancreatic islets after viral infection or treatment with double-stranded RNA (dsRNA), a mimic of viral infection, is associated with the onset of type 1 diabetes. However, how IFNα contributes to the onset of type 1 diabetes is obscure. In this study, we found that 2-5A-dependent RNase L (RNase L), an IFNα-inducible enzyme that functions in the antiviral and antiproliferative activities of IFN, played an important role in dsRNA-induced onset of type 1 diabetes. Using RNase L-deficient, rat insulin promoter-B7.1 transgenic mice, which are more vulnerable to harmful environmental factors such as viral infection, we demonstrated that deficiency of RNase L in mice resulted in a significant delay of diabetes onset induced by polyinosinic:polycytidylic acid (poly I:C), a type of synthetic dsRNA, and streptozotocin, a drug which can artificially induce type 1-like diabetes in experimental animals. Immunohistochemical staining results indicated that the population of infiltrated CD8(+)T cells was remarkably reduced in the islets of RNase L-deficient mice, indicating that RNase L may contribute to type 1 diabetes onset through regulating immune responses. Furthermore, RNase L was responsible for the expression of certain proinflammatory genes in the pancreas under induced conditions. Our findings provide new insights into the molecular mechanism underlying β-cell destruction and may indicate novel therapeutic strategies for treatment and prevention of the disease based on the selective regulation and inhibition of RNase L.