Transfer experiments of iNKT cell subsets reveal the pathogenic role of CD4− iNKT cells containing the iNKT17 cell population in the development of diabetes. Reconstitution of immunodeficient

NOD mice with CD4− iNKT cells enhanced the incidence of diabetes after injection of a low dose of BDC2.5 T cells. Similar exacerbation of diabetes incidence was observed this website after reconstitution with the NK1.1− CD4− iNKT cell population, which exhibits a high frequency of iNKT17 cells. However, due to cell number limitations most of our experiments were performed with the whole CD4− iNKT cell population. Treatment with anti-IL-17 antibodies abolished the pathogenic role of CD4− iNKT cells suggesting that iNKT17 cells are the critical players in the exacerbation MLN8237 of diabetes, however, we cannot rule out that other cell types producing IL-17 are also participating.

Unfortunately, we could not directly demonstrate that only iNKT17 cells were involved in the deleterious effect of CD4− iNKT cells since there is presently no specific surface marker to purify this cell population. IFN-γ is also produced by CD4− iNKT cells and this cytokine could also participate in the exacerbation of diabetes; however, no exacerbation was observed after reconstitution with NK1.1+ CD4− iNKT cells producing high amounts of IFN-γ but low levels of IL-17. Of note, CD4− iNKT cells alone do not induce diabetes after transfer into immunodeficient NOD mice (data not shown). Therefore, we can propose that iNKT17 cells enhanced diabetes Calpain incidence through different mechanisms. In vitro data have shown that IL-17 synergizes with other cytokines

such as IFN-γ and IL-1α/β to induce iNOS expression and subsequent NO production in insulinoma cells or in pancreatic islets of NOD mice 42. Similarly in the pancreas, IL-17 produced by iNKT cells could synergize with IFN-γ secreted by BDC2.5 T cells to induce high expression of NO in β-cells resulting in their destruction. A deleterious loop could take place since β-cell death induced by NO would promote self-antigen presentation by DCs to BDC2.5 T cells. This mechanism could explain the higher frequency of BDC2.5 T cells observed in the PLNs and the pancreas of mice transferred with CD4− iNKT cells as compared with mice devoid of iNKT cells. Furthermore, it has been shown that IL-17A and IL-17F can induce CXCL10 chemokine expression in lung epithelial cells 43, 44. Production of CXCL10 by pancreatic β-cells could contribute to the recruitment of auto reactive T cells expressing the CXCR3 chemokine receptor as previously shown in several mouse models of type 1 diabetes (T10) 45, 46. Thus, iNKT17 cells might not be involved in the initiation of the insulitis but rather could participate in the exacerbation of -β-cell death and diabetes onset. Our data reveal a functional dichotomy between CD4+ and CD4− iNKT cell subsets in the control of diabetes development.