Helios expression defines two distinct populations of Foxp3+ regulatory T cells

The transcription factor Helios is expressed in a subset of Foxp3 + Tregs and we have proposed that Helios is a marker of thymic derived Treg (tTreg). Other studies have suggested that Helios is primarily a marker of T cell activation. In order to study the two Treg subpopulations, we have generated Helios-GFP reporter mice and crossed them to Foxp3-RFP reporter mice. The expression pattern of Helios in the reporter mice is similar to that detected by intracellular staining. When Foxp3 + Helios + and Foxp3 + Helios − were isolated by FACS and transferred to normal mice, both phenotypes were stable. Both populations expressed a highly demethylated TSDR. A comparison of the two populations using RNA-Seq demonstrated 600 differentially expressed genes (500 higher in Helios + , 100 higher in Helios − ). The Helios + population expressed a more activated (Ly-6C − ) phenotype and had slightly higher suppressive capability in vitro. Both subsets were equivalent in their ability to suppress IBD in vivo, but the Helios + subset was more effective in the protection of RAG −/− mice from disease induced by transfer of splenocytes from scurfy mice. Thus, Helios expression can differentiate two distinct populations of Treg and may differentiate peripherally derived Treg (pTreg) from tTreg. This research was supported by the Intramural Research Program of the NIH, NIAID.