Identification of Cellular Sources of IL-2 Needed for Regulatory T Cell Development and Homeostasis

The cytokine IL-2 is critical for promoting the development, homeostasis, and function of regulatory T (Treg) cells. The cellular sources of IL-2 that promote these processes remain unclear. T cells, B cells, and dendritic cells (DCs) are known to make IL-2 in peripheral tissues. We found that T cells and DCs in the thymus also make IL-2. To identify cellular sources of IL-2 in Treg cell development and homeostasis, we used mice to selectively delete in T cells, B cells, and DCs. Because IL-15 can partially substitute for IL-2 in Treg cell development, we carried out the majority of these studies on an background. Deletion of in B cells, DCs, or both these subsets had no effect on Treg cell development, either in wild-type (WT) or mice. Deletion of in T cells had minimal effects in WT mice but virtually eliminated developing Treg cells in mice. In the spleen and most peripheral lymphoid organs, deletion of in B cells, DCs, or both subsets had no effect on Treg cell homeostasis. In contrast, deletion of in T cells led to a significant decrease in Treg cells in either WT or mice. The one exception was the mesenteric lymph nodes where significantly fewer Treg cells were observed when was deleted in both T cells and DCs. Thus, T cells are the sole source of IL-2 needed for Treg cell development, but DCs can contribute to Treg cell homeostasis in select organs.