The molecular mechanism of the extrathymic generation of adaptive, or inducible, CD4+Foxp3+ regulatory T cells (iTregs) remains incompletely defined. We show that exposure of splenic CD4+CD25 +Foxp3- cells to IL-2, but not other common g-chain cytokines, resulted in Stat5 phosphorylation and induced Foxp3 expression in ∼10% of the cells. Thus, IL-2/Stat5 signaling may be critical for Foxp3 induction in peripheral CD4+CD25+Foxp3- iTreg precursors. In this study, to further define the role of IL-2 in the formation of iTreg precursors as well as their subsequent Foxp3 expression, we designed a two-step iTreg differentiation model. During the initial " conditioning" step, CD4+CD25-Foxp3- naive T cells were activated by TCR stimulation. Inhibition of IL-2 signaling via Jak3-Stat5 was required during this step to generate CD4+CD25 +Foxp3- cells containing iTreg precursors. During the subsequent Foxp3-induction step driven by cytokines, IL-2 was the most potent cytokine to induce Foxp3 expression in these iTreg precursors. This two-step method generated a large number of iTregs with relatively stable expression of Foxp3, which were able to prevent CD4+CD45RBhigh cell-mediated colitis in Rag1-/- mice. In consideration of this information, whereas initial inhibition of IL-2 signaling upon T cell priming generates iTreg precursors, subsequent activation of IL-2 signaling in these precursors induces the expression of Foxp3. These findings advance the understanding of iTreg differentiation and may facilitate the therapeutic use of iTregs in immune disorders.
ASJC Scopus subject areas
- Immunology and Allergy