Transciptome of ex vivo-isolated Foxp3+/-RORγt+/- CD4+ T cell populations

Foxp3-expressing regulatory (Treg) T cells are essential for immunological tolerance, where loss of this transcription factor leads to uncontrolled T cell responses and their associated clinical presentation of systemic autoimmunity in mice and humans. Importantly, Foxp3+ Tregs result from different origins and are either generated in the thymus (tTreg) or from conventional CD4+ T cells in the periphery (pTreg). In addition, Treg cells may adopt specific effector Treg phenotypes, reflecting the diversity of functional demands in the different tissues of the body. Here, we report that Foxp3+ T cells expressing the Th17 master transcription factor, RORγt, represent a stable effector Treg lineage that is specifically enriched in intestinal organs and gut-associated lymphoid tissues in mice possessing a complex microbial microflora. Simultaneous expression of Foxp3 and RORγt promotes the transcription of both Treg- and Th17-associated genes in Foxp3+RORγt+ T cells; however, epigenetic profiling of the Treg-specific demethylated region (TSDR) and other Treg-associated genes revealed a high degree of similarity between conventional Tregs and Foxp3+RORγt+ T cells, indicating that these cells have a stable regulatory, rather than inflammatory, function. Indeed, adoptive transfer of Foxp3+RORγt+ T cells in the context of T cell transfer colitis not only confirmed their Treg function and lineage stability in vivo, it also revealed a significantly enhanced regulatory capacity as compared to RORγt+ Treg cells. Thus, our data suggest that RORγt expression in Tregs is essential for optimal regulation of gut-specific immune responses, which renders them an important effector Treg lineage in the intestinal system. To study the global relationship in their gene expression profiles, we sorted Foxp3-RORγt- CD4+ T cells, Foxp3+(RORγt-) Treg cells, RORγt+(Foxp3-) and Foxp3+RORγt+ T cells from splenocytes, peripheral LN and mesenteric LN cells pooled together in order to avoid bias due to a specific tissue location.