Reciprocal Expression of IL-35 and IL-10 Defines Two Distinct Effector Treg Subsets that Are Required for Maintenance of Immune Tolerance

Regulatory T cells (Tregs) can exert their functions through multiple suppressive mechanisms; however, it is unclear how Tregs exactly employ these mechanisms. In this study, we found that interleukin-35 (IL-35)-producing Tregs were a distinct effector population from the IL-10-producing subset. We also revealed that these two subsets of effector Tregs have different transcription factor dependency. Terminal differentiation regulator Blimp1 was only critical for IL-10 production, but not for IL-35; Foxp3 was essential for IL-35 but dispensable for IL-10 production. Furthermore, we demonstrated that IL-35-producing and IL-10-producing Tregs have a different activation status, do not share the same geographic locations in secondary lymphoid organs, and work in a complementary way to prevent autoimmunity. Thus, our study highlights the importance of effector Treg generation. We also provide evidence of Treg activation status tuning the generation of distinct effector Treg subsets, which work cooperatively to maintain immune tolerance.