MneSCs exert a supportive role in establishing a pregnancy-friendly microenvironment by inhibiting TH17 polarization.

• MenSCs downregulate RORC and inhibit T CD4 + TH17 polarization. • MenSCs managed to generate Tregs in a TH17 favored condition. • Inhibition of PGE2 synergize with the capacity of MenSCs to hinder TH17 differentiation. • MenSCs produce a considerable amount of IDO and increased Treg/Th17 ratio. Uncontrolled TH17 differentiation has been suggested to play a role in the pathogenesis of pregnancy loss. We recently showed that menstrual blood stromal/stem cells (MenSCs) alter functional features of natural killer cells. Here, we hypothesized that MenSCs could modulate differentiation of TH17 cells. MenSCs were collected from 18 apparently healthy women and characterized. Bone marrow mesenchymal stem cells (BMSCs) served as a control. TH17 polarization and proliferation of purified T CD4+ cells were assessed by flow cytometry in a well-defined co-culture system containing T CD4+ cells and MenSCs or BMSCs. Indoleamine 2,3-Dioxygenase (IDO) activity was evaluated in MenSC and BMSC culture supernatants by a colorimetric assay. The impact of MenSCs on expression of transcription factors, RORC, T-bet, Gata3, NRP-1 and Helios were studied by qPCR. MenSCs significantly inhibited TH17 differentiation (p = 0.0383) and percentage of the cells co-expressing IL-17 and IFN-γ (p = 0.0023). PGE2 blockade significantly reduced percentage and proliferation of T CD4+IL-17+ (p = 0.003, p = 0.0018), T CD4+ IFN-γ+ (p = 0.002, p = 0.0022) and T CD4+IL-17+ IFN-γ+ (p = 0.004, p = 0.02) cells. MenSCs produced a considerable activity of IDO (p = 0.0002), induced a significant rise in the Treg frequency (p = 0.0091) and a sharp increase in TH17/Tregs ratio (p = 0.0022). MenSCs increased expression of NRP1 (p = 0.001), while downregulated expression of RORC in T cells (p = 0.001). Our results suggest a supportive role for MenSCs in establishing a pregnancy-friendly microenvironment in the uterus and put forth the idea that inherent abnormalities of MenSCs may be a basis for dysregulated endometrial immune network leading to pregnancy loss. [ABSTRACT FROM AUTHOR]