Characterization of the role of major histocompatibility complex in type 1 diabetes recurrence after islet transplantation.

BACKGROUND: Major histocompatibility complex (MHC) molecules are essential determinants of beta-cell destruction in type 1 diabetes (T1D). MHC class I- or class II-null nonobese diabetic (NOD) mice do not spontaneously develop autoimmune diabetes and are resistant to adoptive transfer of disease. Both CD4+ and CD8+ T cells are associated with graft destruction after syngeneic islet transplantation. MHC molecules within the graft (i.e., on beta-cells or donor lymphocytes) may influence the interactions between antigen presenting cells and effector T cells and, therefore, the survival outcome of the graft. METHODS: Donor islets from NOD mice deficient in one or both of beta2-microglobulin and class II transactivator genes were transplanted into diabetic NOD mice. Immunohistochemistry was performed to identify the phenotype of infiltrating cells and to assess graft insulin production. The presence of cytokines in the grafts was assayed by reverse transcription polymerase chain reaction. RESULTS: MHC class II-null islets demonstrated rates of rejection comparable with control wild-type (wt) islets. In contrast, MHC class I- and II-null islets demonstrated indefinite survival (over 100 days). Infiltrates of both failed and surviving grafts were comprised of cytotoxic lymphocytes (CTL), helper T cells, and macrophages. Grafts also showed the presence of both Th1- and Th2-type cytokines (interleukin [IL]-2, IL-4, IL-10, and interferon-gamma), independent of graft status. CONCLUSIONS: These results demonstrate the primary importance of MHC class I molecules in the pathogenesis of diabetes recurrence postislet transplantation. Conversely, MHC class II expression is not a necessary mechanistic component of transplant destruction. In addition, these results implicate MHC class I-restricted CTLs but not MHC class II-restricted T cells in disease recurrence.

Interleukin-4 but not interleukin-10 protects against spontaneous and recurrent type 1 diabetes by activated CD1d-restricted invariant natural killer T-cells.

In nonobese diabetic (NOD) mice, a deficiency in the number and function of invariant natural killer T-cells (iNKT cells) contributes to the onset of type 1 diabetes. The activation of CD1d-restricted iNKT cells by alpha-galactosylceramide (alpha-GalCer) corrects these deficiencies and protects against spontaneous and recurrent type 1 diabetes. Although interleukin (IL)-4 and IL-10 have been implicated in alpha-GalCer-induced protection from type 1 diabetes, a precise role for these cytokines in iNKT cell regulation of susceptibility to type 1 diabetes has not been identified. Here we use NOD.IL-4(-/-) and NOD.IL-10(-/-) knockout mice to further evaluate the roles of IL-4 and IL-10 in alpha-GalCer-induced protection from type 1 diabetes. We found that IL-4 but not IL-10 expression mediates protection against spontaneous type 1 diabetes, recurrent type 1 diabetes, and prolonged syngeneic islet graft function. Increased transforming growth factor-beta gene expression in pancreatic lymph nodes may be involved in alpha-GalCer-mediated protection in NOD.IL-10(-/-) knockout mice. Unlike the requirement of IL-7 and IL-15 to maintain iNKT cell homeostasis, IL-4 and IL-10 are not required for alpha-GalCer-induced iNKT cell expansion and/or survival. Our data identify an important role for IL-4 in the protection against type 1 diabetes by activated iNKT cells, and these findings have important implications for cytokine-based therapy of type 1 diabetes and islet transplantation.

Insulin-like growth factor (IGF)-I/IGF-binding protein-3 complex: therapeutic efficacy and mechanism of protection against type 1 diabetes.

IGF-I regulates islet beta-cell growth, survival, and metabolism and protects against type 1 diabetes (T1D). However, the therapeutic efficacy of free IGF-I may be limited by its biological half-life in vivo. We investigated whether prolongation of its half-life as an IGF-I/IGF binding protein (IGFBP)-3 complex affords increased protection against T1D and whether this occurs by influencing T cell function and/or islet beta-cell growth and survival. Administration of IGF-I either alone or as an IGF-I/IGFBP-3 complex reduced the severity of insulitis and delayed the onset of T1D in nonobese diabetic mice, but IGF-I/IGFBP-3 was significantly more effective. Protection from T1D elicited by IGF-I/IGFBP-3 was mediated by up-regulated CCL4 and down-regulated CCL3 gene expression in pancreatic draining lymph nodes, activation of the phosphatidylinositol 3-kinase and Akt/protein kinase B signaling pathway of beta-cells, reduced beta-cell apoptosis, and stimulation of beta-cell replication. Reduced beta-cell apoptosis resulted from elevated Bcl-2 and Bcl-X(L) activity and diminished caspase-9 activity, indicating a novel role for a mitochondrial-dependent pathway of beta-cell death. Thus, IGF-I/IGFBP-3 affords more efficient protection from insulitis, beta-cell destruction, and T1D than IGF-I, and this complex may represent an efficacious therapeutic treatment for the prevention of T1D.

Blockade of tumor necrosis factor-related apoptosis-inducing ligand exacerbates type 1 diabetes in NOD mice.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is expressed in different tissues and cells, including pancreas and lymphocytes, and can induce apoptosis in various tumor cells but not in most normal cells. The specific roles of TRAIL in health and disease remain unclear. Here we show by cDNA array analyses that TRAIL gene expression is upregulated in pancreatic islets during the development of autoimmune type 1 diabetes in nonobese diabetic (NOD) mice and in Min6 islet beta-cells activated by TNF-alpha + interferon-gamma. However, stimulation of freshly isolated pancreatic islets or Min6 cells with TRAIL did not induce their apoptosis. TRAIL blockade exacerbates the onset of type 1 diabetes in NOD.Scid recipients of transferred diabetogenic T-cells and in cyclophosphamide-treated NOD mice. TRAIL inhibits the proliferation of NOD diabetogenic T-cells by suppressing interleukin (IL)-2 production and cell cycle progression, and this inhibition can be rescued in the presence of exogenous IL-2. cDNA array and Western blot analyses indicate that TRAIL upregulates the expression of the cdk inhibitor p27(kip1). Our data suggest that TRAIL is an important immune regulator of the development of type 1 diabetes.

Regulation of autoimmune disease by natural killer T cells.

Natural killer T (NKT) cells express phenotypic characteristics shared by conventional natural killer cells and T cells, and reside in several primary and secondary lymphoid as well as nonlymphoid organs. Although these cells possess important effector functions in immunity against cancer and microbial pathogens, their immunoregulatory function has received much recent attention. There is convincing evidence to suggest a regulatory role for these cells in the control of susceptibility to autoimmune disease. NKT cells are reduced in number and function in autoimmune disease prone mice and humans. Studies conducted in mice have shown that transfer of NKT cells to disease-susceptible recipients prevents the development of autoimmune disease. The recent discovery that alpha-galactosylceramide, a glycolipid, can specifically target NKT cells expressing the invariant T cell receptor (TCR) to proliferate and produce an array of regulatory cytokines and chemokines has generated considerable interest to utilize these cells as targets of new therapeutic interventions for the immunoregulation of autoimmune disease

Regulatory natural killer T cells protect against spontaneous and recurrent type 1 diabetes.

Autoimmune diseases, especially type 1 diabetes (T1D), may be caused by dysregulation of the immune system, which leads to hyporesponsiveness of regulatory T helper 2 (Th2) cells and promotion of autoimmune Th1 cells. Natural killer T (NKT) cells, which comprise a minor subpopulation of T cells, play a critical role in immunoregulation as a result of a rapid burst of IL-4 and IFN-gamma secretion. These cells are functionally and numerically deficient in individuals at risk of T1D, as well as in nonobese diabetic (NOD) mice. It is conceivable that protection from T1D may be achieved by correction of this deficiency. Alpha-galactosylceramide (alpha-GalCer) specifically binds to NKT cells in a CD1-dependent manner and stimulates these cells to proliferate and to produce various cytokines, including IFN-gamma, IL-4, and IL-10. In this review, we present evidence that a multiple-dose alpha-GalCer treatment regimen, which is known to promote a dominant Th2 environment, can prevent the onset of spontaneous and cyclophosphamide (CY)-accelerated T1D. This protection is associated with elevated IL-4 and IL-10 in the spleen and pancreas of protected female NOD mice. Concomitantly, IFN-gamma levels are reduced in both tissues. More importantly, the protective effect of gamma-GalCer in CY-accelerated T1D is abrogated by the in vivo blockade of IL-10 activity. We also show that alpha-GalCer treatment significantly prolongs syngeneic islet graft survival in recipient diabetic NOD mice. These findings raise the possibility that alpha-GalCer treatment may be used therapeutically to prevent the onset and recurrence of human T1D.

Role of donor MHC class III genes in the destruction of transplanted islets in NOD mice.

MHC class III genes are important in immune regulation and inflammation, and the gene products of this region are well conserved between species. Their role in diabetes is, however, unknown. We used islets from NOD mice that lacked expression of both MHC class I and class II molecules to test the effect of class III differences on the injury of transplanted NOD islets. Loss of islet MHC class I was highly protective, while deletion of MHC class II had no benefit on islet survival. However the combined absence of both MHC class I and class II expression by NOD islets resulted in a delayed form of injury, when islets were transplanted to NOD mice. As neither MHC class I or II molecules were expressed by donor islet tissue, these results suggest a previously unrecognized and important contribution of MHC class III differences on islet injury following transplantation.

ICA69(null) nonobese diabetic mice develop diabetes, but resist disease acceleration by cyclophosphamide.

ICA69 (islet cell Ag 69 kDa) is a diabetes-associated autoantigen with high expression levels in beta cells and brain. Its function is unknown, but knockout of its Caenorhabditis elegans homologue, ric-19, compromised neurotransmission. We disrupted the murine gene, ica-1, in 129-strain mice. These animals aged normally, but speed-congenic ICA69(null) nonobese diabetic (NOD) mice developed mid-life lethality, reminiscent of NOD-specific, late lethal seizures in glutamic acid decarboxylase 65-deficient mice. In contrast to wild-type and heterozygous animals, ICA69(null) NOD congenics fail to generate, even after immunization, cross-reactive T cells that recognize the dominant Tep69 epitope in ICA69, and its environmental mimicry Ag, the ABBOS epitope in BSA. This antigenic mimicry is thus driven by the endogenous self Ag, and not initiated by the environmental mimic. Insulitis, spontaneous, and adoptively transferred diabetes develop normally in ICA69(null) NOD congenics. Like glutamic acid decarboxylase 65, ICA69 is not an obligate autoantigen in diabetes. Unexpectedly, ICA69(null) NOD mice were resistant to cyclophosphamide (CY)-accelerated diabetes. Transplantation experiments with hemopoietic and islet tissue linked CY resistance to ICA69 deficiency in islets. CY-accelerated diabetes involves not only ablation of lymphoid cells, but ICA69-dependent drug toxicity in beta cells that boosts autoreactivity in the regenerating lymphoid system.