Loss of Bcl3 influences gene expression in Tregs and Treg subsets [Bcl3-WT_Treg_bulkRNAseq]

Peripherally induced regulatory T cells (pTregs) expressing the retinoic acid receptor-related orphan-receptor gamma t (RORγt) are indispensable for intestinal immune homeostasis. Previous studies have determined the role of the atypical NFκB inhibitor Bcl3 in the development of colitis. In this study we analyzed the influence of Bcl3 on pTreg development and functionality in healthy mice and under colitogenic conditions. Our findings reveal that expression of Bcl3, in health, limits not just the development of pTregs in a T cell intrinsic manner but also the formation of a RORγt+Helios+ double positive subset (DPTreg) expressing an activated transcriptional profile. Consequently, loss of Bcl3 in Tregs does not impede their suppressive capacity in a model of T cell transfer colitis but moreover leads to increased production of anti-inflammatory cytokines IL-10 and TGFβ. We further demonstrate that lack of Bcl3 in Tregs results in trans-differentiation towards Th17-like cells. Finally, we provide a Bcl3 dependent gene signature in pTregs including altered signaling of the cytokines IL-2, IL-6 and TNFα. We therefore conclude that expression of Bcl3 regulates the sensitivity of Tregs towards homeostatic cytokines and consequently limits the formation of an unphysiological number of RORγt+ Tregs.