TGFβ in the context of an inflammatory cytokine milieu supports de novo differentiation of IL-17-producing T cells

We describe de novo generation of IL-17-producing T cells from naive CD4 T cells, induced in cocultures of naive CD4 T cells and naturally occurring CD4(+) CD25(+) T cells (Treg) in the presence of TLR3, TLR4, or TLR9 stimuli. Treg can be substituted by TGF beta 1, which, together with the proinflammatory cytokine IL-6, supports the differentiation of IL-17-producing T cells, a process that is amplified by IL-1 beta and TNF alpha. We could not detect a role for IL-23 in the differentiation of IL-17-producing T cells but confirmed its importance for their survival and expansion. Transcription factors GATA-3 and T-bet, as well as its target Hlx, are absent in IL-17-producing T cells, and they do not express the negative regulator for TGF beta signaling, Smad7. Our data indicate that, in the presence of IL-6, TGF beta 1 subverts Th1 and Th2 differentiation for the generation of IL-17-producing T cells.