Loss of invariant chain protects nonobese diabetic mice against type 1 diabetes

The invariant (Ii) chain acts as an essential chaperone to promote MHC class II surface expression, Ag presentation, and selection of CD4(+) T cells. We have examined its role in the development of type 1 diabetes in NOD mice and show that Ii chain-deficient NOD mice fail to develop type 1 diabetes. Surprisingly, Ii chain functional loss fails to disrupt in vitro presentation of islet Ags, in the context of NOD I-A(g7) molecules. Moreover, pathogenic effector cells could be shown to be present in Ii chain-deficient NOD mice because they were able to transfer diabetes to NOD.scid recipients. The ability of these cells to transfer diabetes was markedly enhanced by depletion of CD25 cells coupled with in vivo anti-CD25 treatment of recipient mice. The numbers of CD4(+)CD25(+)Foxp3(+) T cells in thymus and periphery of Ii chain-deficient NOD mice were similar to those found in normal NOD mice, in contrast to conventional CD4(+) T cells whose numbers were reduced. This suggests that regulatory T cells are unaffected in their selection and survival by the absence of Ii chain and that an alteration in the balance of effector to regulatory T cells contributes to diabetes prevention.     

Prevention of diabetes in nonobese diabetic mice mediated by CD1d-restricted nonclassical NKT cells

A role for regulatory lymphocytes has been demonstrated in the pathogenesis of type 1 diabetes in the NOD mouse but the nature of these cells is debated. CD1d-restricted NKT lymphocytes have been implicated in this process. Previous reports of reduced diabetes incidence in NOD mice in which the numbers of NKT cells are artificially increased have been attributed to the enhanced production of IL-4 by these cells and a role for classical NKT cells, using the Valpha14-Jalpha18 rearrangement. We now show that overexpression in NOD mice of CD1d-restricted TCR Valpha3.2(+)Vbeta9(+) NKT cells producing high levels of IFN-gamma but low amounts of IL-4 leads to prevention of type 1 diabetes, demonstrating a role for nonclassical CD1d-restricted NKT cells in the regulation of autoimmune diabetes.     

The role of Gr1+ cells after anti-CD20 treatment in type 1 diabetes in nonobese diabetic mice

Studies suggest that Gr1(+)CD11b(+) cells have immunoregulatory function, and these cells may play an important role in autoimmune diseases. In this study, we investigated the regulatory role of Gr1(+)CD11b(+) cells in protecting against type 1 diabetes in NOD mice. In this study, we showed that temporary B cell depletion induced the expansion of Gr1(+)CD11b(+) cells. Gr1(+)CD11b(+) cells not only directly suppress diabetogenic T cell function but also can induce regulatory T cell differentiation in a TGF-β-dependent manner. Furthermore, we found that Gr1(+)CD11b(+) cells could suppress diabetogenic CD4 and CD8 T cell function in an IL-10-, NO-, and cell contact-dependent manner. Interestingly, single anti-Gr1 mAb treatment can also induce a transient expansion of Gr1(+)CD11b(+) cells that delayed diabetes development in NOD mice. Our data suggest that Gr1(+)CD11b(+) cells contribute to the establishment of immune tolerance to pancreatic islet autoimmunity. Manipulation of Gr1(+)CD11b(+) cells could be considered as a novel immunotherapy for the prevention of type 1 diabetes.     

Salmonella typhimurium infection in nonobese diabetic mice generates immunomodulatory dendritic cells able to prevent type 1 diabetes

Infection, commencing across a wide age range, with a live, attenuated strain of Salmonella typhimurium, will halt the development of type 1 diabetes in the NOD mouse. The protective mechanism appears to involve the regulation of autoreactive T cells in a manner associated with long lasting changes in the innate immune compartment of these mice. We show in this study that autoreactive T cell priming and trafficking are altered in mice that have been infected previously by S. typhimurium. These changes are associated with sustained alterations in patterns of chemokine expression. We find that small numbers of dendritic cells from mice that have been previously infected with, but cleared all trace of a S. typhimurium infection are able to prevent the development of diabetes in the highly synchronized and aggressive cyclophosphamide-induced model. The effects we observe on autoreactive T cell trafficking are recapitulated by the immunomodulatory dendritic cell transfers in the cyclophosphamide model.     

IFN beta accelerates autoimmune type 1 diabetes in nonobese diabetic mice and breaks the tolerance to beta cells in nondiabetes-prone mice

Genetic and environmental factors are decisive in the etiology of type 1 diabetes. Viruses have been proposed as a triggering environmental event and some evidences have been reported: type I IFNs exist in the pancreata of diabetic patients and transgenic mice expressing these cytokines in beta cells develop diabetes. To determine the role of IFNbeta in diabetes, we studied transgenic mice expressing human IFNbeta in the beta cells. Autoimmune features were found: MHC class I islet hyperexpression, T and B cells infiltrating the islets and transfer of the disease by lymphocytes. Moreover, the expression of beta(2)-microglobulin, preproinsulin, and glucagon in the thymus was not altered by IFNbeta, thus suggesting that the disease is caused by a local effect of IFNbeta, strong enough to break the peripheral tolerance to beta cells. This is the first report of the generation of NOD (a model of spontaneous autoimmune diabetes) and nonobese-resistant (its homologous resistant) transgenic mice expressing a type I IFN in the islets: transgenic NOD and nonobese-resistant mice developed accelerated autoimmune diabetes with a high incidence of the disease. These results indicate that the antiviral cytokine IFNbeta breaks peripheral tolerance to beta cells, influences the insulitis progression and contributes to autoimmunity in diabetes and nondiabetes- prone mice.     

Systemic overexpression of IL-10 induces CD4+CD25+ cell populations in vivo and ameliorates type 1 diabetes in nonobese diabetic mice in a dose-dependent fashion

Early systemic treatment of nonobese diabetic mice with high doses of recombinant adeno-associated virus (rAAV) vector expressing murine IL-10 prevents type 1 diabetes. To determine the therapeutic parameters and immunological mechanisms underlying this observation, female nonobese diabetic mice at 4, 8, and 12 wk of age were given a single i.m. injection of rAAV-murine IL-10 (10(4), 10(6), 10(8), and 10(9) infectious units (IU)), rAAV-vector expressing truncated murine IL-10 fragment (10(9) IU), or saline. Transduction with rAAV-IL-10 at 10(9) IU completely prevented diabetes in all animals injected at all time points, including, surprisingly, 12-wk-old animals. Treatment with 10(8) IU provided no protection in the 12-wk-old injected mice, partial prevention in 8-wk-old mice, and full protection in all animals injected at 4 wk of age. All other treatment groups developed diabetes at a similar rate. The rAAV-IL-10 therapy attenuated pancreatic insulitis, decreased MHC II expression on CD11b+ cells, increased the population of CD11b+ cells, and modulated insulin autoantibody production. Interestingly, rAAV-IL-10 therapy dramatically increased the percentage of CD4+CD25+ regulatory T cells. Adoptive transfer studies suggest that rAAV-IL-10 treatment alters the capacity of splenocytes to impart type 1 diabetes in recipient animals. This study indicates the potential for immunomodulatory gene therapy to prevent autoimmune diseases, including type 1 diabetes, and implicates IL-10 as a molecule capable of increasing the percentages of regulatory cells in vivo.     

Testing the role of P2X7 receptors in the development of type 1 diabetes in nonobese diabetic mice

Although P2rx7 has been proposed as a type 1 diabetes (T1D) susceptibility gene in NOD mice, its potential pathogenic role has not been directly determined. To test this possibility, we generated a new NOD stock deficient in P2X(7) receptors. T1D development was not altered by P2X(7) ablation. Previous studies found CD38 knockout (KO) NOD mice developed accelerated T1D partly because of a loss of CD4(+) invariant NKT (iNKT) cells and Foxp3(+) regulatory T cells (Tregs). These immunoregulatory T cell populations are highly sensitive to NAD-induced cell death activated by ADP ribosyltransferase-2 (ART2)-mediated ADP ribosylation of P2X(7) receptors. Therefore, we asked whether T1D acceleration was suppressed in a double-KO NOD stock lacking both P2X(7) and CD38 by rescuing CD4(+) iNKT cells and Tregs from NAD-induced cell death. We demonstrated that P2X(7) was required for T1D acceleration induced by CD38 deficiency. The CD38 KO-induced defects in homeostasis of CD4(+) iNKT cells and Tregs were corrected by coablation of P2X(7). T1D acceleration in CD38-deficient NOD mice also requires ART2 expression. If increased ADP ribosylation of P2X(7) in CD38-deficient NOD mice underlies disease acceleration, then a comparable T1D incidence should be induced by coablation of both CD38 and ART2, or CD38 and P2X(7). However, a previously established NOD stock deficient in both CD38 and ART2 expression is T1D resistant. This study demonstrated the presence of a T1D resistance gene closely linked to the ablated Cd38 allele in the previously reported NOD stock also lacking ART2, but not in the newly generated CD38/P2X(7) double-KO line.     

Characterization of peripheral regulatory CD4+ T cells that prevent diabetes onset in nonobese diabetic mice

The period that precedes onset of insulin-dependent diabetes mellitus corresponds to an active dynamic state in which pathogenic autoreactive T cells are kept from destroying beta cells by regulatory T cells. In prediabetic nonobese diabetic (NOD) mice, CD4+ splenocytes were shown to prevent diabetes transfer in immunodeficient NOD recipients. We now demonstrate that regulatory splenocytes belong to the CD4+ CD62Lhigh T cell subset that comprises a vast majority of naive cells producing low levels of IL-2 and IFN-gamma and no IL-4 and IL-10 upon in vitro stimulation. Consistently, the inhibition of diabetes transfer was not mediated by IL-4 and IL-10. Regulatory cells homed to the pancreas and modified the migration of diabetogenic to the islets, which resulted in a decreased insulitis severity. The efficiency of CD62L+ T cells was dose dependent, independent of sex and disease prevalence. Protection mechanisms did not involve the CD62L molecule, an observation that may relate to the fact that CD4+ CD62Lhigh lymph node cells were less potent than their splenic counterparts. Regulatory T cells were detectable after weaning and persist until disease onset, sustaining the notion that diabetes is a late and abrupt event. Thus, the CD62L molecule appears as a unique marker that can discriminate diabetogenic (previously shown to be CD62L-) from regulatory T cells. The phenotypic and functional characteristics of protective CD4+ CD62L+ cells suggest they are different from Th2-, Tr1-, and NK T-type cells, reported to be implicated in the control of diabetes in NOD mice, and may represent a new immunoregulatory population.     

CD8+ T cell tolerance in nonobese diabetic mice is restored by insulin-dependent diabetes resistance alleles

Although candidate genes controlling autoimmune disease can now be identified, a major challenge that remains is defining the resulting cellular events mediated by each locus. In the current study we have used NOD-InsHA transgenic mice that express the influenza hemagglutinin (HA) as an islet Ag to compare the fate of HA-specific CD8+ T cells in diabetes susceptible NOD-InsHA mice with that observed in diabetes-resistant congenic mice having protective alleles at insulin-dependent diabetes (Idd) 3, Idd5.1, and Idd5.2 (Idd3/5 strain) or at Idd9.1, Idd9.2, and Idd9.3 (Idd9 strain). We demonstrate that protection from diabetes in each case is correlated with functional tolerance of endogenous islet-specific CD8+ T cells. However, by following the fate of naive, CFSE-labeled, islet Ag-specific CD8+ (HA-specific clone-4) or CD4+ (BDC2.5) T cells, we observed that tolerance is achieved differently in each protected strain. In Idd3/5 mice, tolerance occurs during the initial activation of islet Ag-specific CD8+ and CD4+ T cells in the pancreatic lymph nodes where CD25+ regulatory T cells (Tregs) effectively prevent their accumulation. In contrast, resistance alleles in Idd9 mice do not prevent the accumulation of islet Ag-specific CD8+ and CD4+ T cells in the pancreatic lymph nodes, indicating that tolerance occurs at a later checkpoint. These results underscore the variety of ways that autoimmunity can be prevented and identify the elimination of islet-specific CD8+ T cells as a common indicator of high-level protection.     

Elimination of maternally transmitted autoantibodies prevents diabetes in nonobese diabetic mice

The influence of maternally transmitted immunoglobulins on the development of autoimmune diabetes mellitus in genetically susceptible human progeny remains unknown. Given the presence of islet beta cell-reactive autoantibodies in prediabetic nonobese diabetic (NOD) mice, we abrogated the maternal transmission of such antibodies in order to assess their influence on the susceptibility of progeny to diabetes. First, we used B cell-deficient NOD mothers to eliminate the transmission of maternal immunoglobulins. In a complementary approach, we used immunoglobulin transgenic NOD mothers to exclude autoreactive specificities from the maternal B-cell repertoire. Finally, we implanted NOD embryos in pseudopregnant mothers of a non-autoimmune strain. The NOD progeny in all three groups were protected from spontaneous diabetes. These findings demonstrate that the maternal transmission of antibodies is a critical environmental parameter influencing the ontogeny of T cell-mediated destruction of islet beta cells in NOD mice. It will be important to definitively determine whether the transmission of maternal autoantibodies in humans affects diabetes progression in susceptible offspring.     

Up-regulation of CD1d expression restores the immunoregulatory function of NKT cells and prevents autoimmune diabetes in nonobese diabetic mice

The immunoregulatory function of NKT cells is crucial for prevention of autoimmunity. The prototypical NKT cell Ag alpha-galactosylceramide is not present in mammalian cells, and little is known about the mechanism responsible for NKT cell recruitment and activation. Up-regulation of CD1d, the NKT cell restriction molecule, expressed on mononuclear cells infiltrating the target organ, could represent the physiological trigger for NKT cells to self-contain T cell immunity and to prevent autoimmune disease. Recognition of CD1d, either by itself or bound to self-ligands (selfCD1d), could drive NKT cells toward an immunoregulatory phenotype. Hence, ineffective NKT cell-mediated immunoregulation in autoimmune-prone individuals including nonobese diabetic (NOD) mice could be related to defective signals that regulate CD1d expression at time and site of autoimmunity. To test this hypothesis, we transgenically overexpressed CD1d molecules under the control of the insulin promoter within the pancreatic islets of NOD mice (insCD1d). Recognition of overexpressed CD1d molecules rescued NKT cell immunoregulatory function and prevented autoimmune diabetes in insCD1d transgenic NOD mice. Protection from diabetes was associated with a biased IL-4-secreting cytokine phenotype of NKT cells and alteration of the cytokine microenvironment in the pancreatic lymph nodes of transgenic mice. The net effect was a reduced development of the autoimmune T cell repertoire. Our findings suggest that up-regulation of CD1d expression during inflammation is critical to maintain T cell homeostasis and to prevent autoimmunity.     

Neonatal injection of CD3 antibody into nonobese diabetic mice reduces the incidence of insulitis and diabetes

Over 80% of nonobese diabetic (NOD) mice develop lymphocytic infiltrates of their pancreatic islets (insulitis) by 6 wk of age and 50% of the females are diabetic by 6 mo of age. The incidence of insulitis in NOD mice injected once as neonates with 250 micrograms of the CD3 antibody, 145.2C11, was 8% at 10 wk of age, increasing to 25% at 32 wk of age. Fewer than 10% of these animals developed diabetes by 8 mo of age. Neonatal administration of 145.2C11 reduced the proliferative responses of spleen cells to mitogen stimulation 2 and 4 wk postinjection and expression of TCR was reduced 1 to 5 wk postinjection. The percentage of CD4 and CD8 cells in the spleen was transiently reduced after injection and the frequency of Pgp-1+-high cells (putative memory cells) was increased 2 to 4 wk postinjection, suggesting that in vivo administration of the antibody caused some T cells to divide as well as transiently reducing T cell numbers. IL-2R expression was not detected on spleen cells in the 4 wk after antibody injection. The phenotypic and functional changes after neonatal CD3 antibody injection resolved by 8 wk of age. The control and injected mice grew normally and made equivalent IgG antibody responses to injected human IgG. Neonatally injected 145.2C11 antibody was cleared from the circulation with a terminal half-life approximating to 21 days but greater than 90% of antigen binding activity was lost 6 days after injection. Protection from diabetes did not follow neonatal elimination of T cells with CD4 and CD8 antibodies, nor the injection of a TCR subset antibody, F23.1. Our data suggest that the neonatal T cell repertoire is open to modulation by a single injection of a CD3 antibody and they offer a new experimental approach to immunotherapy in an animal model of type 1 diabetes.     

Molecular genetic analysis of the Idd4 locus implicates the IFN response in type 1 diabetes susceptibility in nonobese diabetic mice

High-resolution mapping and identification of the genes responsible for type 1 diabetes (T1D) has proved difficult because of the multigenic etiology and low penetrance of the disease phenotype in linkage studies. Mouse congenic strains have been useful in refining Idd susceptibility loci in the NOD mouse model and providing a framework for identification of genes underlying complex autoimmune syndromes. Previously, we used NOD and a nonobese diabetes-resistant strain to map the susceptibility to T1D to the Idd4 locus on chromosome 11. Here, we report high-resolution mapping of this locus to 1.4 megabases. The NOD Idd4 locus was fully sequenced, permitting a detailed comparison with C57BL/6 and DBA/2J strains, the progenitors of T1D resistance alleles found in the nonobese diabetes-resistant strain. Gene expression arrays and quantitative real-time PCR were used to prioritize Idd4 candidate genes by comparing macrophages/dendritic cells from congenic strains where allelic variation was confined to the Idd4 interval. The differentially expressed genes either were mapped to Idd4 or were components of the IFN response pathway regulated in trans by Idd4. Reflecting central roles of Idd4 genes in Ag presentation, arachidonic acid metabolism and inflammation, phagocytosis, and lymphocyte trafficking, our combined analyses identified Alox15, Alox12e, Psmb6, Pld2, and Cxcl16 as excellent candidate genes for the effects of the Idd4 locus.     

Pancreas-infiltrating Th1 cells and diabetes develop in IL-12-deficient nonobese diabetic mice.

IL-12 and IL-12 antagonist administration to nonobese diabetic (NOD) mice accelerates and prevents insulin-dependent diabetes mellitus (IDDM), respectively. To further define the role of endogenous IL-12 in the development of diabetogenic Th1 cells, IL-12-deficient NOD mice were generated and analyzed. Th1 responses to exogenous Ags were reduced by approximately 80% in draining lymph nodes of these mice, and addition of IL-12, but not IL-18, restored Th1 development in vitro, indicating a nonredundant role of IL-12. Moreover, spontaneous Th1 responses to a self Ag, the tyrosine phosphatase-like IA-2, were undetectable in lymphoid organs from IL-12-deficient, in contrast to wild-type, NOD mice. Nevertheless, wild-type and IL-12-deficient NOD mice developed similar insulitis and IDDM. Both in wild-type and IL-12-deficient NOD mice, approximately 20% of pancreas-infiltrating CD4+ T cells produced IFN-gamma, whereas very few produced IL-10 or IL-4, indicating that IDDM was associated with a type 1 T cell infiltrate in the target organ. T cell recruitment in the pancreas seemed favored in IL-12-deficient NOD mice, as revealed by increased P-selectin ligand expression on pancreas-infiltrating T cells, and this could, at least in part, compensate for the defective Th1 cell pool recruitable from peripheral lymphoid organs. Residual Th1 cells could also accumulate in the pancreas of IL-12-deficient NOD mice because Th2 cells were not induced, in contrast to wild-type NOD mice treated with an IL-12 antagonist. Thus, a regulatory pathway seems necessary to counteract the pathogenic Th1 cells that develop in the absence of IL-12 in a spontaneous chronic progressive autoimmune disease under polygenic control, such as IDDM.     

NK3-like NK cells are involved in protective effect of polyinosinic-polycytidylic acid on type 1 diabetes in nonobese diabetic mice

Type 1 diabetes in NOD mice is characterized by the uncontrolled Th1 immune responses and deficiency of regulatory or suppressor cells. Previous study has shown that NOD mice treated with polyinosinic-polycytidylic acid (poly(I:C)) have a markedly reduced incidence of diabetes, but the underlying mechanisms remain unclear. In this study, we report that the prevention of diabetes by poly(I:C) is associated with the formation of Th2-enriched environment in spleen and pancreas. We further show that the prevention of diabetes and the formation of Th2-enriched environment depend on the presence of NK cells. Long-term poly(I:C)-treated NK cells exhibit a NK3-like phenotype, and are involved in the induction of Th2 bias of spleen cells in response to islet autoantigens via TGF-beta-dependent manner. Therefore, NK cells mediate the protective effect of poly(I:C) possibly through the promotion of Th2 bias of immune responses. These findings suggest that NK cells can participate in the regulation of autoimmune diabetes.     

NKT cells stimulated by long fatty acyl chain sulfatides significantly reduces the incidence of type 1 diabetes in nonobese diabetic mice

Sulfatide-reactive type II NKT cells have been shown to regulate autoimmunity and anti-tumor immunity. Although, two major isoforms of sulfatide, C16:0 and C24:0, are enriched in the pancreas, their relative role in autoimmune diabetes is not known. Here, we report that sulfatide/CD1d-tetramer(+) cells accumulate in the draining pancreatic lymph nodes, and that treatment of NOD mice with sulfatide or C24:0 was more efficient than C16:0 in stimulating the NKT cell-mediated transfer of a delay in onset from T1D into NOD.Scid recipients. Using NOD.CD1d(-/-) mice, we show that this delay of T1D is CD1d-dependent. Interestingly, the latter delay or protection from T1D is associated with the enhanced secretion of IL-10 rather than IFN-g by C24:0-treated CD4(+) T cells and the deviation of the islet-reactive diabetogenic T cell response. Both C16:0 and C24:0 sulfatide isoforms are unable to activate and expand type I iNKT cells. Collectively, these data suggest that C24:0 stimulated type II NKT cells may regulate protection from T1D by activating DCs to secrete IL-10 and suppress the activation and expansion of type I iNKT cells and diabetogenic T cells. Our results raise the possibility that C24:0 may be used therapeutically to delay the onset and protect from T1D in humans.     

Early Th1 response in unprimed nonobese diabetic mice to the tyrosine phosphatase-like insulinoma-associated protein 2, an autoantigen in type 1 diabetes

The insulinoma-associated protein 2 (IA-2) is a phosphatase-like autoantigen inducing T and B cell responses associated with human insulin-dependent diabetes mellitus (IDDM). We now report that T cell responses to IA-2 can also be detected in the nonobese diabetic (NOD) mouse, a model of human IDDM. Cytokine secretion in response to purified mouse rIA-2, characterized by high IFN-gamma and relatively low IL-10 and IL-6 secretion, was elicited in spleen cells from unprimed NOD mice. Conversely, no response to IA-2 was induced in spleen cells from BALB/c, C57BL/6, or Biozzi AB/H mice that express, like NOD, the I-A(g7) class II molecule, but are not susceptible to spontaneous IDDM. The IA-2-induced IFN-gamma response in NOD spleen cells could already be detected at 3 wk and peaked at 8 wk of age, whereas the IL-10 secretion was maximal at 4 wk of age and then waned. IA-2-dependent IFN-gamma secretion was induced in CD4(+) cells from spleen as well as pancreatic and mesenteric lymph nodes. It required Ag presentation by I-A(g7) molecules and engagement of the CD4 coreceptor. Interestingly, cytokines were produced in the absence of cell proliferation and IL-2 secretion. The biological relevance of the response to IA-2 is indicated by the enhanced IDDM following a single injection of the recombinant protein emulsified in IFA into 18-day-old NOD mice. In addition, IFN-gamma production in response to IA-2 and IDDM acceleration could be induced by IL-12 administration to 12-day-old NOD mice. These results identify IA-2 as an early T cell-inducing autoantigen in the NOD mouse and indicate a role for the IA-2-induced Th1 cell response in IDDM pathogenesis.     

ICOS mediates the development of insulin-dependent diabetes mellitus in nonobese diabetic mice

Initiation of diabetes in NOD mice can be mediated by the costimulatory signals received by T cells. The ICOS is found on Ag-experienced T cells where it acts as a potent regulator of T cell responses. To determine the function of ICOS in diabetes, we followed the course of autoimmune disease and examined T cells in ICOS-deficient NOD mice. The presence of ICOS was indispensable for the development of insulitis and hyperglycemia in NOD mice. In T cells, the deletion of ICOS resulted in a decreased production of the Th1 cytokine IFN-gamma, whereas the numbers of regulatory T cells remained unchanged. We conclude that ICOS is critically important for the induction of the autoimmune process that leads to diabetes.     

Inosine protects against the development of diabetes in multiple-low-dose streptozotocin and nonobese diabetic mouse models of type 1 diabetes

Inosine, a naturally occurring purine, was long considered to be an inactive metabolite of adenosine. However, recently inosine has been shown to be an immunomodulator and anti-inflammatory agent. The aim of this study was to determine whether inosine influences anti-inflammatory effects and affects the development of type 1 diabetes in murine models. Type 1 diabetes was induced either chemically by streptozotocin or genetically using the nonobese diabetic mouse (NOD) model. Mice were treated with inosine (100 or 200 mg kg(-1)d(-1)d) and diabetes incidence was monitored. The effect of inosine on pancreas immune cell infiltration, oxidative stress, and cytokine profile also was determined. For the transplantation model islets were placed under the renal capsule of NOD mice and inosine (200 mg kg(-1)d d(-1)d) treatment started the day of islet transplantation. Graft rejection was diagnosed by return of hyperglycemia accompanied by glucosuria and ketonuria. Inosine reduced the incidence of diabetes in both streptozotocin-induced diabetes and spontaneous diabetes in NOD mice. Inosine decreased pancreatic leukocyte infiltration and oxidative stress in addition to switching the cytokine profile from a Th1 to a Th2 profile. Inosine prolonged pancreatic islet graft survival, increased the number of surviving beta cells, and reduced the number of infiltrating leukocytes. Inosine protects against both the development of diabetes and against the rejection of transplanted islets. The purine exerts anti-inflammatory effects in the pancreas, which is its likely mode of action. The use of inosine should be considered as a potential preventative therapy in humans susceptible to developing Type 1 diabetes and as a possible antirejection therapy for islet transplant recipients.