Background/Purpose: Our previous reports showed that the development of collagen-induced arthritis was suppressed in T-bet transgenic (T-bet Tg) mice. The regulatory mechanism might relate to dysfunction of Th-17 cell differentiation by the overexpression of T-bet gene. The purpose of this study is to clarify the effect of T-bet overexpression on Th-17 cell differentiation.

Methods:   T-bet overexpressing IFNγ deficient (T-bet Tg/IFNγ^-/-) mice were generated by crossing T-bet Tg mice under the promoter of CD2 gene with IFNγ deficient (IFNγ^-/-) mice. CD4⁺ T cells from C57BL/6 (WT), T-bet Tg, or T-bet Tg/IFNγ^-/- mice were cultured for Th-17 differentiation, and the cytokine production (IFNγ, IL-17) and the expression of transcription factors (T-bet, RORγt) was analyzed. We examined the expression of IL-6 receptor (IL-6R) constituted by CD126 and CD130 and the phosphorylation of STAT3 by IL-6 stimulation of CD4⁺ T cells. The mRNA expression of transcription factors (tbx21, rorc, stat3, stat1, runx1, irf4, nfkbiz, and ahr) associated with the Th-17 differentiation were examined in the Th-17 condition. We transduced retrovirus expressing T-bet gene into naïve CD4⁺ T cells of WT or IFNγ^-/- mice, and investigated cytokines and transcription factors expression. Moreover, we examined the expression of aryl hydrocarbon receptor (AHR) in Th-17 condition by flow cytometry in both T-bet Tg mice and retroviral transduction of T-bet gene. We investigated the facilitation of Th-17 differentiation by the addition of AHR ligand, 6-formylindolo [3,2-b] carbazole (FICZ), and analyzed the mRNA expression of cyp1a1, which was the AHR target gene.

Results:   In both T-bet Tg and T-bet Tg/IFNγ^-/- mice, RORγt expression and IL-17 production were inhibited in Th-17 condition, and IL-6R expression and STAT3 phosphorylation of CD4⁺ T cells were decreased. We also observed the inhibition of IL-17 production in CD4⁺ T cells of WT and IFNγ^-/- mice transduced with T-bet, whereas T-bet transduction in vitro had no effects on IL-6 receptor expression and STAT3 phosphorylation. The mRNA expression of nfkbiz was up-regulated, but rorc and ahr were down-regulated with T-bet overexpression in both T-bet Tg mice and T-bet gene transduction under the Th-17 condition. FACS analyses revealed that the expression of AHR was significantly decreased not only in T-bet Tg and T-bet Tg/IFNγ^-/- mice but also in T-bet gene transduced cells from both WT and IFNγ^-/- mice. IL-17 production and the expression of cyp1a1 by T-bet overexpression were not promoted by the addition of FICZ.

Conclusion:   T-bet overexpression in CD4+ T cells repressed Th-17 differentiation by suppression of IL-17 production, RORgt expression, and AHR expression. Our findings support the possibility that regulatory mechanisms of Th-17 differentiation by T-bet overexpression might be due to the IFNγ-independent suppression of AHR.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/t-bet-regulates-ahr-mediated-th-17-differentiation-independently-of-ifn%ce%b3/