The Pathogenesis And Immunotherapy For Type 1 Diabetes In NOD Mice

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized bydestruction of insulin-producing pancreaticβcells, which is a complicated processthat likely results from the multiple defects of tolerance mechanisms. Development ofT1D is genetically controlled and thought to be initiated in susceptible individuals byenvironmental factors such as virus infections. The NOD mouse strain is an excellentmodel of T1D and an important tool for exploring tolerance mechanisms. The NODmouse strain developed spontaneous autoimmune diabetes, and the incidence ofspontaneous diabetes in the NOD mouse is 60% to 80% in females and 20% to 30%in males. Histological studies have shown that few immune cells infiltrate in isletsuntil about 3 to 4 weeks of age, the most mice show severe insulitis by 10 weeks ofage. Diabetes onset firstly occurs at 12 to 14 weeks of age in female NOD mice. Thepathological characteristics and clinical manifestations are similar with human T1D,including the presence of insulitis, pancreas-specific autoantibodies, autoreactiveCD4+ T cells and genetic linkage to type 1 diabetes found in humans. However, thepathogenesis of T1D is still not clear. In order to reveal the fundamental diseasemechanisms, researchers have used a wide variety of tools to study the mice duringthe past twenty years. In addition, researchers have developed a number of therapeuticinterventions in the animal model that have now been applied to human therapiesrecently.In order to further clarify the role of TH17 cells in type 1 diabetes, we comparedthe proportion of TH17 cells from spleen and the level of IL-17 from serum andpancreata in NOD mice with age-matched BALB/c and C57BL/6 mice. Our resultsshowed that the proportion of TH17 cells from spleen increased significantly in NODmice. In addition, the level of IL-17 was also significantly increased from pancreasand serum in NOD mice. The results suggested that TH17 cells were closely related toT1D.Functional abnormalities of DCs have been demonstrated in type 1 diabetic patients and in NOD mice. First, we found that the frequency and the absolute numberof DCs were significantly decreased and the levels of the pro-inflammatory cytokineswere elevated in NOD mice compared to age-matched BALB/c and C57BL/6 mice.Then, our results demonstrated that CFA treatment effectively reduced the incidenceof T1D and alleviated insulitis. CFA could increase significantly the proportion ofDCs and recover the function of DCs, however, the frequency of the regulatory Tcells, NK and NKT cells was not significantly changed after CFA treatment. Finally,our results suggested that the IFN-γinduced by CFA administration preventeddiabetes through a mechanism of inhibition of pathogenic IL-17 production in NODmice.For the sake of exploring the defense mechanisms, we design two sets oftreatment strategies to prevent T1D in NOD mice. First, we performed CFAprotective model and found a single CFA treatment can effectively prevent T1D.Because of the obvious side effects, CFA is not suitable for use in humans. The next,we found that intermittent treatment with 200 ng of IL-12 can prevent diabetes andenhance survival in NOD mice. Moreover, IL-12, a possible therapeutic agent againstinfectious diseases and tumors, may also be valuable in the clinical treatment ofdiabetes.The dendritic cell is one important source of IL-12 which is a potentimmunoregulatory molecule that is a pivotal Th1-associated cytokine. To examinewhether IL-12 treatment Prevents diabetes in NOD mice, we performed the treatmentwith various dose of IL-12. The findings indicated that Intermittent treatment withvarious dose of IL-12, especially the IL-12 (200ng) ground, delayed and preventeddiabetes. IL-12 treatment effectively suppressed the insulitis and increased the numberof healthy islets, meanwhile, the level of IL-17 was significantly decreased and theTH17-associated pro-inflammation cytokines IL-1β, IL-6 and IL-23 were markedlyreduced. More importantly, IL-12 treatment induced the secretion of IFN-γthat ispotent inhibitor of the TH17 cells. Therefore, IFN-γinduced with IntermittentAdministration of IL-12 prevents diabetes by suppress the pathogenicIL-17-producing cells. These results suggested a new strategy for the therapy of T1Dand of other TH17 cell-mediated autoimmune disease. In view of the above results, we can draw a conclusion that the TH17 cells isclosely related to spontaneous diabetes in NOD mice, and the absolute number andthe function of DCs were impaired in NOD mice and that the levels of theTh17-associated pro-inflammatory cytokines, IL-1β, IL-6 and IL-23, were elevated inNOD mice. However, the level of IL-12 and IFN-γwas significantly reduced. UnderCFA and intermittent IL-12 treatment, the pathogenic TH17 cells were obviouslysuppressed by inducing protective IFN-γ.