The effects of IL-2 and Treg cells on dendritic cell homeostasis are mediated indirectly via activation of conventional T cells.

DC homeostasis is influenced by multiple factors, including the availability of GM-CSF and Flt3L, both of which exert positive effects on DC differentiation and survival. IL-2 and Treg cells have recently been proposed as negative regulators of DC numbers. It remains unclear whether their effects in immunosufficient mice are direct, or are mediated via activation of conventional T cells in response to deficiencies of IL-2 and/or Treg cells. Using a number of in vivo models, we have assessed the role of IL-2 and Treg-cell number on conventional splenic and LN DCs. We have found no evidence for a direct role of IL-2 or Treg cells in negatively regulating DC number. Our data indicate that the expansion of DCs in the absence of either IL-2 or Treg cells is an indirect effect secondary to the activation and proliferation of conventional T cells.