Interferon-γ Limits Diabetogenic CD8+ T-Cell Effector Responses in Type 1 Diabetes

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.