Nakashima et al.[48] showed the accumulation of IL-17+ T cells in the deciduas in women MAPK inhibitor with inevitable abortion. Decidual IL-17+ T cells were mostly CD4+ T cells and a few CD8+ cells also expressed IL-17 in this study. In addition, the number of decidual IL-17+ cells was positively correlated with the number of decidual neutrophils. However, they could not find any difference in the number of decidual IL-17+ T cells between women with missed abortion and normal pregnancy. From these results, the authors concluded that decidual IL-17+ cells might be involved in the inflammation of the late stage of abortive process, not the causative factor of abortion.[48] Because their data of IL-17+

cells were limited to inevitable abortion, not to RPL, it may be difficult to generalize the results as the immunologic mechanism of RPL. A series of studies concerning Th17 cells have been reported regarding RPL in the past 2 years. Wang et al.[70] found an increase in Th17 cells in the peripheral blood and decidua of women with unexplained RPL as compared to normal pregnant women. Serum IL-17 and IL-23 levels were significantly higher in women with RPL. Furthermore, Th17-related CHIR-99021 chemical structure molecules such as IL-17, IL-23, and retinoid orphan receptor C (RORC) were significantly expressed in the deciduas of women with RPL. The number of Th17 cells inversely correlated

with that of regulatory T cells in the peripheral blood and deciduas. The same group has reported another Th17 cell study in women with RPL.[73] They found that the proportions of peripheral blood CCR6+ CD4+ T and CCR6+ IL17+ T cells were significantly

elevated in women with RPL as compared to healthy pregnant women undergoing elective abortion. In ex vivo culture study, IL-17 production from CD4+ T cells was significantly higher Dimethyl sulfoxide in women with RPL and regulatory T cells from women with RPL were less suppressive to the expression of IL-17 as compared to control women. Similarly, a decrease in CD4+ CD25bright Foxp3+ regulatory T cells and increase in Th17 cells have been reported in the peripheral blood of women with RPL in comparison with normal healthy pregnant women.[64] The ratio of Th17/regulatory T cells was significantly increased in women with RPL as compared to normal pregnant and non-pregnant women. The proportion of regulatory T cells negatively correlated with the proportion of Th17 cells (Table 1). Serum IL-17 levels correlated positively with Th17 cells and the ratio of Th17/regulatory T cells.[64] These results suggest that regulatory T cells inhibit IL-17 expression and suppressive function of regulatory T cells on Th17 cells may decrease in women with RPL. Our group recently published a study that investigated pro-inflammatory cytokines (TNF-α, IFN-γ, and IL-17), anti-inflammatory cytokine IL-10, and Foxp3 in the PBMCs of idiopathic women with RPL.