CXCR3+ Treg cells suppress Th1-immune responses through expression of the co-inhibitory receptors CD85k and Lag-3

CD4+Foxp3+ Treg cells are essential for maintaining self-tolerance and preventing excessive immune responses. In the context of Th1 immune responses, co-expression of the Th1 transcription factor T-bet with Foxp3 is essential for Treg cells to control Th1 responses. T-bet-dependent expression of CXCR3 directs Tregs to the site of inflammation, however, the suppressive mediators enabling effective control of Th1 responses at this site are unknown. In this study, we determined the signature of CXCR3+ Treg cells arising in Th1 settings and defined universal features of Treg cells in this context using multiple Th1-dominated models. Our analysis defined a set of Th1-specific co-inhibitory receptors that are specifically expressed in Treg cells during Th1 immune responses. Among these, we identified the novel co-inhibitory receptor CD85k as a functional mediator of the enhanced suppression of Th1 effector cells by CXCR3+ Treg cells.