Functional Regulation Of Th17 Cells At Maternal-fetal Interface Of Early Pregnancy In Humans

The embryo expresses antigens foreign to mother, and thus has been viewed as allograft. Induction of maternal tolerance to persistence of the alloantigen is a main purpose for maintenance of pregnancy. It has been proven that maternal-fetal interface exhibits a Th2 bias, including IL-4, IL-5 and IL-10 cytokines during pregnancy. Failure to establish such an immune milieu or Thl bias, such as interferon (IFN)-y and tumor necrosis factor (TNF)-a, is associated with fetal miscarriage. Regulatory T cells (Treg) play an important role in preventing from the autoimmune reaction and rejection of transplantation.The newly described Th17 cells are characterized by the production of IL-17A, IL-17F and IL-22, and are thought to clear extracellular pathogens that are not effectively handled by either Thl or Th2 cells. Mounting data from murine models and human studies of autoimmunity link Th17 to chronic inflammatory diseases. It is also demonstrated that Th17 cells has been implicated in the pathogenesis of several types of cancer and allograft rejection. Now that Th17 cells are in human PBMC, we propose to investigate whether Th17 cells are in human peripheral blood and deciduas during human first-trimester pregnancy, and they affect trophoblast functions.1. Th17 cells increase in decidua and peripheral blood of human first-trimester pregnancyWe found that the percentage of Th17 cells was significantly higher in PBMCs and decidua of first-trimester pregnancy than that of healthy non-pregnancy (1.68%±0.44 vs 0.61%±0.14), while the levels of Th17 cells gradually decreased along with pregnancy continuation to the secondary and third trimester (1.35%±0.57 and 0.86%±0.59). In third trimester, the ratio of Th17 cells was the same as that of healthy non-pregnancy. Th17 cells in the freshly isolated CD4+ T cells were significantly elevated in first-trimester deciduas compared to healthy secretory endometrium (1.53%±0.50 vs 2.84%±0.57 Fig. lb). We also found that the relative numbers of Th17 cells increased more markedly in the decidua than that of the peripheral blood.2. The differentiation of Th17 and Treg cells at maternal-fetal interfaceWe found that 19.5%±1.53% decidual CD4+ T cells were CD4+ CD45RA+ naive T cells in human first-trimester decidua. After the decidual naive CD4+ T cells co-cultured with trophoblasts and/or DSCs for 72h, the naive CD4+ T cells were then collected and analyzed for the percentage of Th17 cells by FCM. We found that trophoblasts, DSCs, especially their co-culture inhibited apparently the differentiation of Th17 cells. It has been demonstrated that this inhibition is via soluble molecules because of similar tendency of Th17 cell ratios between treatment by the co-culture or its supernatants. The supernatants inhibit Th17 cell differentiation, but promote Treg cell differentiation.17-βE2, progesterone and hCG had no effect on the development of Th17 cells. Therefore, the soluble molecules presented at maternal-fetal interface are beneficial for the predominance of Treg to Th17 cells.3. DSCs recruit peripheral Th17 cells into deciduaWe found that both peripheral blood and decidual Th17 cells were effector memory T cells. The expression of CCR6 ligand, CCL20, in human villous and decidual tissues of human first-trimester pregnancy was analyzed by immunohistochemistry. CCL20 was specifically positive on cytomembrane of villous cytotrophoblasts, syncytiotrophoblasts and invasive trophoblast cells in deciduas, and DSCs also expressed CCL20 moderately. Glandular epithelium and endometrial stromal cells (ESCs) of endometrium were weakly positive for CCL20. The freshly isolated peripheral CD4+ T cells were chemotactic to the supernatants from trophoblasts, DSCs or trophoblast-DSC co-culture, and we found that it was DSCs other than trophoblasts that recruited Th17 cells into decidua. Therefore, DSCs may attract selectively Th17 cells into decidua via a series of chemokines.It has been reported that Th17 cells are characterized by the expression of CCR6 and CCR2, and CCR6 is essential for the migration of Th17 cells. We have also found that DSCs released high level of CCR2 ligand, CCL2. We compared the effect of DSC supernatants with or without neutralizing antibody to CCL20 or CCL2 on the migration of Th17 cells. Our data show that anti-CCL2 neutralizing antibody abolishes substantially the migration of Th17 cells induced by DSC supernatants. However, there was no significant difference of Th17 cells migration induced by DSC supernatants with anti-CCL20 neutralizing antibody compared to DSC supernatants without anti-CCL20 neutralizing antibody, suggesting that the CCR2-CCL2 axis in the decidua mediates the localization of decidual Th17 cells.4. Th17 cells induce proliferation and invasion of human first-trimester trophoblast through secreting IL-17We found that trophoblasts and DSCs expressed IL-17 receptor. The supernatants from Th17 cells induced the proliferation and invasion of trophoblast mainly through secreting IL-17, which was similar to the effect of recombinant IL-17.We also found that the supernatants inhibited the apoptosis of trophoblasts via IL-17, suggesting that Th17 cells are involved in human first-trimester placentation.