Abstract

Objective: In humans, multiple genes in the IL-2/IL-2R pathway are associated with T1D. However, no link between IL-2 responsiveness and CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Treg) has been demonstrated in T1D subjects despite the role of these IL-2-dependent cells in controlling autoimmunity. Here, we address whether altered IL-2 responsiveness impacts persistence of FOXP3 expression in Treg of T1D subjects.

Research design and methods: Persistence of Treg was assessed by culturing sorted CD4⁺CD25^hi nTreg with IL-2 and measuring FOXP3 expression over-time by flow cytometry for control and T1D populations. The effects of IL-2 on FOXP3 induction were assessed 48 hours following activation of CD4⁺CD25⁻ T cells with anti-CD3 antibody. Cytokine receptor expression and signaling upon exposure to IL-2, IL-7 and IL-15 was determined by flow cytometry and western blot analysis.

Results: Maintenance of FOXP3 expression in CD4⁺CD25⁺ Treg of T1D was diminished in the presence of IL-2, but not IL-7. Impaired responsiveness was not linked to altered expression of the IL-2R complex. Instead, IL-2R signaling was reduced in Treg and total CD4⁺ T cells of T1D. In some individuals, decreased STAT5 phosphorylation correlated with significantly higher expression of protein tyrosine phosphatase N2 (PTPN2), a negative regulator of IL-2R signaling.

Conclusions: Aberrant IL-2R signaling in CD4⁺ T cells of T1D subjects contributes to decreased persistence of FOXP3 expression that may impact establishment of tolerance. These findings suggest novel targets for treatment of T1D within the IL-2R pathway and suggest that an altered IL-2R signaling signature may be a biomarker for T1D.