Continuous T Cell Receptor Signals Maintain a Functional Regulatory T Cell Pool

• Foxp3 expression and gene-specific hypomethylation are unaffected by TCR ablation
• TCR expression is critical for effector Treg cell differentiation and maintenance
• The homeostatic proliferation of Treg cells depends on TCR signals
• TCR ablation impairs the functional abilities of Treg cells

SummaryRegulatory T (Treg) cells maintain immune homeostasis and prevent inflammatory and autoimmune responses. During development, thymocytes bearing a moderately self-reactive T cell receptor (TCR) can be selected to become Treg cells. Several observations suggest that also in the periphery mature Treg cells continuously receive self-reactive TCR signals. However, the importance of this inherent autoreactivity for Treg cell biology remains poorly defined. To address this open question, we genetically ablated the TCR of mature Treg cells in vivo. These experiments revealed that TCR-induced Treg lineage-defining Foxp3 expression and gene hypomethylation were uncoupled from TCR input in mature Treg cells. However, Treg cell homeostasis, cell-type-specific gene expression and suppressive function critically depend on continuous triggering of their TCR.