Interaction between Kynurenine and Aryl Hydrocarbon Receptor in Regulating the Balance of T helper 17 Cells and Regulatory T-cells in Decidua during Early Gestation

Objective: To investigate whether kynurenine/aryl hydrocarbon receptor (AHR) affects the maternal-fetal tolerance by involving the differentiation of T helper 17 (Th17)/regulatory T (Treg) cells, and to provide theoretical basic for new treatment of unexplained abortion. Methods: Flow cytometry (FCM) was used to detect the expression of AHR in peripheral/decidual CD4(+) T, Treg, and Th17 cells. The effect of Kyn on the differentiation of peripheral/decidual nave T-cells under Treg-/Th17-polarizing condition was detected by FCM; enzyme-linked immunosorbent assay was performed to examine the level of Kyn in villus and decidual tissues from normal pregnancy (NP) and unexplained abortion (UA). Student's t-test in the case of two groups or one-way ANOVA in multiple groups was used. Results: AHR expression in CD4(+) T-cells was decreased in decidua versus blood in early pregnancy (P < 0.0001). Kyn could promote the differentiation of peripheral and decidual nave T-cells to Th17 cells under Treg-polarizing conditions (P < 0.01). There was no statistical significance about the concentration of Kyn in decidual or villi tissues between NP and UA, and compared with NP, the expression of AHR in decidual CD4(+) T-cells from UA was increased (P < 0.001). Conclusions: Kyn/AHR promotes Th17 and restricts Treg cells' differentiation, which is involved in maintaining the balance of Treg/Th17 cells at the maternalufetal interface.