Dendritic cell paracrine IL-2 regulates phenotype and function of CD4+CD25+ Treg cells in vitro. (138.5)

Abstract

Abstract The development, expansion and function of mouse CD4+CD25+ regulatory T cells (Treg) requires intact IL-2 receptor and paracrine IL-2, but the identity of the paracrine supplier remains obscure. Herein we show in mice that Treg suppressive function in vitro depends on IL-2 from dendritic cells (DC). Anti-CD25 blocked not only Treg inhibition of DO11.10 CD4+CD25- effector cells, but also Treg inhibition of DC stimulatory function, suggesting a DC source of IL-2. We showed by IL-2 ELISPOT, intracytoplasmic flow cytometry and RT-PCR, and we confirmed by transfection studies using IL-2-promoter-driven reporters, that splenic and bone marrow-derived DCs constitutively produced IL-2, and that CpG-B increased IL-2 production. Though secreted IL-2 protein was readily detected in DC cultures by ELISPOT, little or no IL-2 protein was detected in DC cultures that contained Treg cells. The addition of anti-CD25 preserved the level of IL-2 protein detected in co-cultures of DC and Treg cells. Tregs failed to maintain levels of CD25 and foxp3 or to suppress CD4+CD25- effector cells proliferation and IL-2 production in cultures where DCs from IL-2 knockout mice were substituted for wild-type DCs. These results show that dendritic cells supply IL-2 to Tregs and that Treg phenotype and inhibitory function critically depends on paracrine IL-2 from dendritic cells.