Essential role of interferon-regulatory factor 4 in regulating diabetogenic CD4+ T and innate immune cells in autoimmune diabetes in NOD mice

Haploinsufficiency of the transcription factor interferon-regulatory factor 4 (IRF4) prevents the onset of spontaneous diabetes in NOD mice. However, the immunological mechanisms of the IRF4-mediated disease regulation remain unclear. This study aims to investigate the role of IRF4 in the pathogenesis of autoimmune diabetes by conducting adoptive transfer experiments using donor IRF4 gene-deficient CD4+ T cells from BDC2.5-transgenic (Tg) NOD mice and recipient Rag1-knockout NOD mice, respectively. Through this approach, we analyzed both clinical and immunological phenotypes of the recipient mice. Additionally, IRF4-deficient BDC2.5 CD4+ T cells were stimulated to assess their immunological and metabolic phenotypes in vitro. The findings revealed that diabetes was completely prevented in the recipients with Irf4-/- T cells and was approximately 50% lower in those with Irf4+/- T cells than in wild type (WT) controls, whereas Irf4-/- recipients with WT T cells only showed a delayed onset of diabetes. Islet-infiltrating T cells isolated from recipients with Irf4+/- T cells exhibited significantly lower proliferation and IFN-γ/IL-17 double-positive cell fraction rates compared with those in WT controls. Irf4-/- BDC2.5 CD4+ T cells stimulated in vitro showed a reduced number of cell divisions, decreased antigen-specific T-cell markers, and impairment of glycolytic capacity compared with those observed in WT controls. We concluded that IRF4 predominantly regulates the diabetogenic potential in a dose-dependent manner by mediating the proliferation and differentiation of islet-infiltrating T cells while playing an adjunctive role in the innate immune responses toward diabetes progression in NOD mice.