ABSTRACT: TNF is a pleiotropic cytokine that exerts immunomodulatory functions mostly mediated by its interaction with the receptor TNFR2, highly expressed by regulatory T cells. However, Tregs can also produce TNF, and the existence of an autocrine TNF-TNFR2 loop has been proposed. Here, we describe that, indeed, both human and mouse Tregs can produce TNF in physiological conditions, in several mouse organs, and in mouse models of chronic inflammation and cancer. However, TNF production and TNFR2 expression are mutually exclusive in Tregs: indeed, TNFR2+ and TNFR2- Treg subsets are respectively poor and strong TNF producers. In TNFR2+ cells, TNF is both transcriptionally and post-transcriptionally controlled, through the repressing activity of microRNA-146a. The two subsets of TNFR2+ and TNFR2- Tregs partially maintain their different ability to produce TNF, when separately stimulated ex vivo. However, when cocultured, the TNFR2+ cells greatly outnumber the TNFR2- counterpart, and induce in TNFR2- cells the upregulation of Foxp3 and TNFR2, an event that is associated with the transfer of cytoplasmic material from TNFR2+ to TNFR2- cells. Functionally, TNFR2+ Tregs are endowed with superior suppressive activity, in association with a better survival in vitro. This phenotype could be attributed to an improved resistance to oxidative stress, as revealed by gene expression analysis and intracellular ROS staining. Overall, our data indicate that Tregs exist in two states, respectively committed to TNF production or TNF sensing through TNFR2, which cooperate in promoting the suppressive function of the whole Treg pool.
