The characteristics of antigenic specificity of memory regulatory t cells in women with unexplained recurrent pregnancy loss.

Regulatory T cells (Tregs) proliferate after encountering the fetal antigen, which plays an important role in maintaining maternal-fetal tolerance. Activated Tregs increase number and function after antigen encounter and develop memory. Upon subsequent antigen exposure, Treg cells re-expand more rapidly. However, the characteristics of memory regulatory T cells (mTregs) during normal pregnancy and unexplained recurrent pregnancy loss (URPL) have not been elucidated well. In this study, we analyzed the proportion of Tregs and mTregs in the peripheral blood and their surface expression of PD-1, CCR6, and HLA-G in normal non-pregnant (n = 20) and pregnant (n = 20) women, and non-pregnant (n = 20) and pregnant URPL (n = 20) women. We found that the proportions of mTregs in lymphocytes, CD3+ T cells, CD4+ T cells, and Tregs were lower in pregnant URPL patients than in normal pregnant women. The proportions of CD4+CD45RO+ Th cells in lymphocytes, CD3+ T, and CD4+ T cells in the pregnant URPL group were the highest among the four groups (P < 0.05). There were no significant differences among the other three groups (P > 0.05). The proportions of CD4+/CCR6+/mTregs, CD4+/PD-1+/mTregs, CD4+/HLA-G+/mTregs were significantly lower in the non-pregnant normal group and non-pregnant URPL group than in normal pregnant group and pregnant URPL group (P < 0.05, respectively). The proportions of CD4+/CCR6+ mTregs, CD4+/PD-1+/mTregs, CD4+/HLA-G+/mTregs were lower in pregnant URPL group than in normal pregnant group (P < 0.05, respectively). These findings indicate that fetal antigen-specific mTregs play an important role in pregnancy maintenance, and the dysregulation of mTreg may contribute to URPL.