Endogenous IL‐2 production governs the in vitro induction of FoxP3‐expressing adaptive Treg in the NOD mouse

Abstract

Lack of self‐tolerance to [beta] cells in Type 1 diabetes (T1D) is in part due to defects in the development and function of FoxP3‐expressing immunoregulatory CD4+ T cells (Treg). IL‐2 has been shown to be involved in Treg differentiation and maintenance. In addition, the IL‐2 gene located in the IDD3 locus is a candidate for diabetes susceptibility. To explore the role of IL‐2 in the development of adaptive Treg and T1D, NOD mice congenic for the C57BL/6 IDD3 interval(NOD.IDD3) and which have a reduced incidence of diabetes were studied. Stimulated CD25‐CD4+ T cells from NOD.IDD3 versus NOD mice produced ~2‐fold more IL‐2. To test the respective T cells to differentiate into adaptive Treg, CD25‐CD4+ T cells were stimulated with anti‐CD3 & CD28 antibodies and varying concentrations of TGF‐β1. A 3‐fold increase in FoxP3‐expressing cells was detected in NOD.IDD3 versus NOD cultures. Notably, the addition of anti‐IL‐2 ab blocked the induction of FoxP3‐expressing T cells in both sets of cultures. Furthermore, an equivalent frequency of FoxP3‐expressing T cells was detected in NOD.IDD3 and NOD cultures supplemented with IL‐2. These results demonstrate that elevated IL‐2 production by stimulated NOD.IDD3 CD25‐CD4+ T cells increases the efficiency of adaptive Treg differentiation. Furthermore, reduced production of IL‐2 by CD25‐CD4+ T cells in NOD mice may limit the induction of adaptive Treg and contribute to T1D.