Modulation of Cytokine Secretion Allows CD4 T Cells Secreting IL-10 and IL-17 to Simultaneously Participate in Maintaining Tolerance and Immunity.

CD4 T cells secreting IL-10 or IL-17 are frequent at mucosal sites, where their equilibrium is important for simultaneously maintaining tolerance and immunity to the resident microbiota. The mode of action of these cells, however, is as yet incompletely understood. In this study, we have combined ex vivo analysis of CD4 T cells producing IL-10 or/and IL-17 with assessment of clonal populations isolated ex vivo using a cytokine catch assay. We found that circulating CD4 T cells secreting IL-10 or/and IL-17 ex vivo include both conventional FOXP3- CD4 T cells and FOXP3+ Helios- Treg. Upon assessment of clonal populations derived from single ex vivo isolated cytokine secreting cells, we found that IL-10 or/and IL-17 secreting cells prevalently secrete one or the other cytokine depending on the type of stimulation, the time after stimulation and the presence of microbial products. Namely, IL-10 secretion by clonal cells was prevalent at early time points after TCR mediated stimulation, was independent of co-stimulation and was increased in the presence of the microbial fermentation product butyrate. In contrast, IL-17 secretion was higher at later time points after TCR mediated stimulation and in the presence of co-stimulatory signals. Taken together, these results provide insights into the mechanisms that, through modulation of cytokine secretion depending on conditions, allow IL-10 and IL-17 producing CD4 T cells to contribute to maintain tolerance to microbes locally, while retaining the ability to participate in protective immune responses at distant sites.