JEG-3 Trophoblast Cells Producing Human Chorionic Gonadotropin Promote Conversion of Human CD4+FOXP3- T Cells into CD4+FOXP3+ Regulatory T Cells and Foster T Cell Suppressive Activity.

The pregnancy hormone human Chorionic Gonadotropin (hCG) reportedly modulates innate and adaptive immune responses and contributes thereby to fetal survival. More precisely, hCG has been shown to support human Treg cell homing into the fetal-maternal interface and enhance number and function of Treg cells in murine pregnancy. Here, we aimed to study whether hCG and hCG-producing human trophoblast cell lines induce Treg cells from CD4+FOXP3- T cells and promote T cell suppressive activity. CD4+FOXP3- T cells were isolated from peripheral blood of normal pregnant women and cultured in the presence of hCG-producing (JEG-3, HTR-8) and non-producing (SWAN-71) cell lines. To confirm the participation of hCG in Treg cell conversion, the experiments were performed in the presence of anti-hCG and additional experiments were run with recombinant or urine-purified hCG. After culture the number of CD4+FOXP3+ Treg cells as well as the suppressive capacity of total T cells was assessed. hCG-producing JEG-3 cells as well as recombinant and urine-purified hCG induced CD4+FOXP3+ Treg cells from CD4+FOXP3- T cells. Blockage of hCG impaired Treg cell induction. Moreover, hCG-producing JEG-3 cells increased suppressive activity of CD4+FOXP3- T cells through an antigen-independent pathway. Our results propose another mechanism through which hCG modulates the female immune system during pregnancy in favor of the fetus.

Human chorionic gonadotropin as a central regulator of pregnancy immune tolerance.

Normal pregnancy is characterized by an early expansion of regulatory T cells (Tregs), which is known to contribute to fetal tolerance. However, mechanisms and factors behind Treg expansion are not yet defined. Recently, we proposed that the pregnancy hormone human chorionic gonadotropin (hCG) efficiently attracts human Tregs to trophoblasts, favoring their accumulation locally. In this study, we hypothesized that hCG not only acts as a chemoattractant of Tregs but also plays a central role in pregnancy-induced immune tolerance. Virgin, normal pregnant, and abortion-prone female mice were treated either with 10 IU/ml hCG or PBS at days 0, 2, 4, and 6 of pregnancy. The hCG effect on Treg frequency and cytokine secretion was determined in Foxp3(gfp) females. hCG impact on Treg suppressive capacity was studied in vitro. In vivo, we investigated whether hCG enhances Treg suppressive capacity indirectly by modulating dendritic cell maturation in an established mouse model of disturbed fetal tolerance. Application of hCG increased Treg frequency in vivo and their suppressive activity in vitro. In females having spontaneous abortions, hCG provoked not only an augmentation of Treg numbers, but also normalized fetal abortion rates. hCG-generated Tregs were fully functional and could confer tolerance when adoptively transferred. hCG also retained dendritic cells in a tolerogenic state that is likely to contribute to both Treg expansion and prevention of abortion. Our results position hCG in a novel, so far unknown role as modulator of immune tolerance during pregnancy.

Luteinizing hormone contributes to fetal tolerance by regulating adaptive immune responses.

PROBLEM: Pregnancy hormones were proposed to be crucially involved in fetal tolerance. Recently, we showed that human chorionic gonadotropin (hCG) not only increases the number and activity of regulatory T cells (Treg) but also retains tolerogenic dendritic cells (DCs). Here, we investigate whether the highly homologous luteinizing hormone (LH) modulates Treg number and DC phenotype and thereby supports pregnancy. METHOD OF STUDY: Abortion-prone females were treated with LH or PBS on different gestation days. Pregnancy outcome and the number and phenotype of Treg and DCs were evaluated in the periphery and locally. RESULTS: We discovered that LH application completely prevented fetal rejection in abortion-prone females. This protective effect was associated with a Treg augmentation peripherally and locally. Moreover, LH reduced the number of total and mature DCs. CONCLUSION: Our data suggest that LH, similar to hCG, is involved in the regulation of adaptive immune responses, thus contributing to fetal tolerance.