Background: Polymorphisms within the IL2RA gene (CD25) is a risk factor for multiple sclerosis (MS), raising the possibility that IL2 promotes pathogenesis. Though IL2 is a treatment in some autoimmune conditions, its role in MS is poorly understood.
Objectives: The objective was to examine early IL2 dependent activation signals in CD4 and CD8 T cell effector populations and Treg cells in relapsing multiple sclerosis (RMS) patients and healthy controls (HC). The goal was to test the hypothesis that strength of IL2 signals will be different between treatment naive RMS and HC that will likely reflect on disease progression and/or severity.
Methods: We stimulated PBMC from HC (15) and newly diagnosed RMS (37) with IL2 and quantified the activation of STAT5, primary response of IL2. Treatment was not a confounder as all of the RMS samples were treatment naïve at the time of collection. The level of activation of STAT5 (pSTAT-Y694) in CD4 and CD8 effector T cells (naïve, central memory, effector memory and terminal effectors) and Tregs was determined by multi-dimensional phosphoflow cytometry. The data were analyzed by conventional gating strategies as well as using unbiased hierarchical, algorithm-based approaches, t-SNE and FlowSOM.
Results: From conventional flow-cytometry analysis, we found that IL2 dependent activation of STAT5 was significantly greater in all CD4 effector T cell populations and in CD8 naïve, central memory and effector memory T cell populations. Notably, the frequency of response was the same in RMS or HC CD4 and CD8 cells but the magnitude of response was quite different. From t-SNE and FlowSOM analysis, we identified non-overlapping populations of IL2 responders between HC and RMS, a finding that was unexpected. Both t-SNE and FlowSOM revealed distinct IL2 responding and non-responding Treg populations between RMS and HC with no difference found on flow cytometry. Stratifying RMS into self-identified racial groups, we observed differences in IL2 responding CD8 T cell populations between African ancestry and European ancestry.
Conclusions: In summary, our data reveal differences in IL2 response within effector and regulatory T cell populations between RMS and HC and between African ancestry and European Ancestry RMS. The correlation of these findings on disease activity and treatment response is being explored.
Supported by DOD grant PR151462 (SLB and CR), 5T32GM008361-26 (BP), AAI fellowship (BP) and R21 MD015319-01 (CR and WM).