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Type 1 diabetes development in the NOD mouse model is widely reported to be dependent on high-level production by autoreactive CD4+ and CD8+ T cells of interferon-γ (IFN-γ), generally considered a proinflammatory cytokine. However, IFN-γ can also participate in tolerance-induction pathways, indicating it is not solely proinflammatory. This study addresses how IFN-γ can suppress activation of diabetogenic CD8+ T cells. CD8+ T cells transgenically expressing the diabetogenic AI4 T-cell receptor adoptively transferred disease to otherwise unmanipulated NOD.IFN-γnull , but not standard NOD, mice. AI4 T cells only underwent vigorous intrasplenic proliferation in NOD.IFN-γnull recipients. Disease-protective IFN-γ could be derived from any lymphocyte source and suppressed diabetogenic CD8+ T-cell responses both directly and through an intermediary nonlymphoid cell population. Suppression was not dependent on regulatory T cells, but was associated with increased inhibitory STAT1 to STAT4 expression levels in pathogenic AI4 T cells. Importantly, IFN-γ exposure during activation reduced the cytotoxicity of human-origin type 1 diabetes-relevant autoreactive CD8+ T cells. Collectively, these results indicate that rather than marking the most proinflammatory lymphocytes in diabetes development, IFN-γ production could represent an attempted limitation of pathogenic CD8+ T-cell activation. Thus, great care should be taken when designing possible diabetic intervention approaches modulating IFN-γ production. [ABSTRACT FROM AUTHOR]

NKT cell activation by alpha-galactosylceramide (aGalCer) inhibits autoimmune diabetes in NOD mice, in part by inducing recruitment to pancreatic lymph nodes (PLNs) of mature disease-protective dendritic cells (DCs). However, how activated NKT cells promote DC maturation, and what downstream effect this has on diabetogenic T cells was unknown. Activated NKT cells produce a soluble factor(s) inducing maturation of DC towards a phenotype quite distinct from that generated by anti-CD40 stimulation. With anti-CD40 treatment of DC, it was thought that their enhanced capacity to stimulate the proliferation of T cells was, in part, due to the up-regulation of the costimulatory molecules B7-1 and B7-2. However, when DC were treated with soluble factor(s) from NKT cells they expressed 3 to 4-fold higher numbers of costimulatory molecules per cell but failed to demonstrate the same ability as anti-CD40 treated DC to stimulate the proliferation of a diabetogenic CD8 T cell clone (AI4) in vitro. In the absence of the NAD-glycohydrolase CD38, ADP-ribosyltransferase 2 (ART2) activates the apoptotic deletion of peripheral NKT cells. Due to this further decrease in NKT cell numbers, T1D is accelerated in CD38 deficient NOD mice. Furthermore, unlike in standard NOD mice, aGalCer pretreatment does not protect the CD38 deficient stock from T I D induced by adaptively transferred AI4 T cells. As a consequence of its small size and position in the plasma membrane, the ART2 catalytic site cannot be targeted by conventional antibodies. However, we found due to its small size (15 kDa) allowing for excellent biodistribution and low immunogenicity, a unique llama derived single chain antibody reagent can block ART2 enzymatic activity in vivo. Treatment of CD38 deficient NOD mice with the single chain antibody reagent can enhance the survival of NKT cells and thereby increase their number in PLN and spleen. We are now testing if using this llama single chain antibody to block the normally greatly increased apoptotic loss of NKT cells in CD38 deficient mice, restores the ability of aGalCer to induce T1D protective effects in this stock. [ABSTRACT FROM AUTHOR]