Is TGFβ as an anti-inflammatory cytokine required for differentiation of inflammatory TH17 cells?

Abstract

T-Helper 17 (TH17) cells are a CD4+ TH subset that plays a critical role in the pathophysiology of inflammatory disorders, especially chronic forms. It seems that the derivation of TH17 cells from their precursors take place in inflammatory microenvironment. The role of transforming growth factor (TGF)-β as an anti-inflammatory cytokine in TH17 cell differentiation is controversial. To address some of the discrepancies that exist among different studies, this study was undertaken to more clarify the TGFβ role in human TH17 cell differentiation. Here, CD4+ T-cells were isolated from peripheral blood samples and cultured in X-VIVO 15 serum-free medium. Purified cells were then treated with different combinations of polarizing cytokines (interleukin [IL]1-β, -6, and -23, with or without TGFβ), neutralizing anti-interferon (IFN)-γ and anti-IL-4 antibodies and polyclonal stimulators anti-CD3 and -CD28 antibodies, and then analyzed for IL-17, IFNγ, Foxp3, and CD25 expression by flow cytometry and for release of IL-17, -21, -22, and -10 into culture media by ELISA. The effects of selective inhibition of TGFβ signaling pathway on TH17 cell polarization were also determined by using small molecules SB-431542 and A83-01. The current study found that a combination of pro-inflammatory cytokines, including IL-1β, -6, and -23, but not TGFβ, could be used as a cytokine combination to induce development of human TH17 cells. It was also shown that TGFβ acted as a negative regulator in this regard and also led to reduced IL-17 and IL-22 production while inducing Foxp3 expression. Indeed, blocking of TGFβ signaling pathways by selective inhibitors up-regulated TH17 cell differentiation. From the data here, we concluded that TGFβ down-regulates human TH17 cell differentiation and that a presence of pro-inflammatory cytokines (along with IFNγ and IL-4 neutralizing antibodies) is sufficient for optimal differentiation of human TH17 cells.