Continuous T cell receptor signals maintain a functional regulatory T cell pool

During development, thymocytes bearing a moderately self-reactive T cell receptor (TCR) can be selected to become regulatory T (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. TCRpos (FoxP3+ CD4+ CD25high cells from CαF/F FoxP3 I eGFP mice) and TCRneg (FoxP3+ TCR– CD4+ CD25high cells from Mx-Cre CαF/F FoxP3 I eGFP mice) Treg cells were FACS sorted 6 weeks after poly(I:C) injection. Cells from 3-5 mice were pooled for sorting, and 4 replicates for the controls (TCRpos) as well as 5 replicates for the Mx-Cre (TCRneg) mice were generated. mRNA from 3-5 x 105 cells was purified with a RNeasy Micro kit (Qiagen), amplified, labeled and hybridized to Affymetrix M430 V2 microarrays