Eomesodermin Expression in CD4+ T Cells Restricts Peripheral Foxp3 Induction

Abstract

CD4+ T cells polarize into effector Th subsets characterized by signature transcription factors and cytokines. Although T-bet drives Th1 responses and represses the alternative Th2, Th17, and Foxp3+ regulatory T cell fates, the role of the T-bet–related transcription factor eomesodermin (Eomes) in CD4+ T cells is less well understood. In this study, we analyze the expression and effects of Eomes in mouse CD4+ T lymphocytes. We find that Eomes is readily expressed in activated CD4+ Th1 T cells in vivo. Eomes+ CD4+ T cells accumulated in old mice, under lymphopenic conditions in a T cell transfer model of colitis, and upon oral Ag administration. However, despite its expression, genetic deletion of Eomes in CD4+ T cells did not impact on IFN-γ production nor increase Th2 or Th17 responses. In contrast, Eomes deficiency favored the accumulation of Foxp3+ cells in old mice, after in vivo differentiation of Eomes-deficient naive CD4+ T cells, and in response to oral Ag in a cell-intrinsic way. Enforced Eomes expression during in vitro regulatory T cell induction also reduced Foxp3 transcription. Likewise, bystander Eomes-deficient CD4+ T cells were more efficient at protecting from experimental autoimmune encephalitis compared with wild-type CD4+ T cells. This enhanced capacity of Eomes-deficient CD4+ T cells to inhibit EAE in trans was associated with an enhanced frequency of Foxp3+ cells. Our data identify a novel role for Eomes in CD4+ T cells and indicate that Eomes expression may act by limiting Foxp3 induction, which may contribute to the association of EOMES to susceptibility to multiple sclerosis.