Reduced IL-2R signaling in T1D subjects is pervasive in the memory CD4 T effector compartment and is mediated through intrinsic mechanisms

Abstract

Abstract The IL-2/IL-2R pathway is strongly implicated in type 1 diabetes (T1D). Yet, identifying the functional significance and underlying mechanisms of altered IL-2R signaling in T1D has been challenging due to variance in the subjects, cell types and the assays utilized. We performed a large, well-matched, cross-sectional study of control and T1D subjects (n>75 subjects per group), with an optimized IL-2/pSTAT5 assay (internal control CoV <7%). We found reduced responses to IL-2 in memory CD4 Treg and Teff cell populations of T1D subjects relative to controls. Known genetic risk alleles accounted for some, but not all, of the reduction in pSTAT5. To determine additional factors underlying reduced IL-2R signaling, we interrogated CD4 Teff cells of control and T1D subjects held constant for risk alleles associated with IL-2R signaling. IL-2 signaling in T1D memory CD4 Teff cells remained significantly lower than controls after in vitro activation and proliferation, suggesting a role for intrinsic factors. These intrinsic factors were not caused by divergence to MAPK or Akt signaling pathways, as measured by western blot. Instead, differences in basal activation state prior to in vitro activation correlated with IL-2 response, as measured by targeted flow and qPCR of activation and negative regulation. Thus, multiple factors including genetics, disease and activation state contribute to natural variation in IL-2 responsiveness, requiring precise assays and well-defined cohorts to reach solid conclusions. These findings offer a better understanding of the mechanisms contributing to reduced IL-2R signaling in T1D and have implications for development of more targeted IL-2-based therapies and stratification of patients for therapy.