Regulatory T cells (Treg cells or Tregs) belong to a subset of CD4 T cells that express the biomarkers FOXP3 and CD25 in addition to CD4 and function to keep immune homeostasis by suppressing the development of effector T cells in particular Th17 cells that participate in the pathogenesis of a number of autoimmune diseases by producing IL-17 which promotes inflammation [67–70]. The gene discussed is IL17A; the disease is autoimmune disease.