CD4+Foxp3+ Treg consist of two indistinguishable subsets induced in either the thymus or the periphery. In addition to their suppressive activities, IL-6 can convert natural Treg to pro-inflammatory IL-17-producing cells, but those induced with IL-2 and TGF-beta remain Treg. Unlike mouse CD4+CD25(-) cells, which rapidly become polyclonal Foxp3+CD25+ Treg when activated appropriately with IL-2 and TGF-beta, human T cells require multiple stimulations to become similar suppressor cells.