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 Foxp3gfp 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.

Various physiologically relevant processes are regulated by the interaction of the receptor tyrosine kinase (c-Kit) and its ligand stem cell factor (SCF), with SCF known to be the most important growth factor for mast cells (MCs). In spite of their traditional role in allergic disorders and innate immunity, MCs have lately emerged as versatile modulators of a variety of physiologic and pathologic processes. Here we show that MCs are critical for pregnancy success. Uterine MCs presented a unique phenotype, accumulated during receptivity and expanded upon pregnancy establishment. KitW-sh/W-sh mice, whose MC deficiency is based on restricted c-Kit gene expression, exhibited severely impaired implantation, which could be completely rescued by systemic or local transfer of wild-type bone marrow-derived MCs. Transferred wild-type MCs favored normal implantation, induced optimal spiral artery remodeling and promoted the expression of MC proteases, transforming growth factor-β and connective tissue growth factor. MCs contributed to trophoblast survival, placentation and fetal growth through secretion of the glycan-binding protein galectin-1. Our data unveil unrecognized roles for MCs at the fetomaternal interface with critical implications in reproductive medicine.

BackgroundMast cells (MCs) have long been suspected as important players for implantation based on the fact that their degranulation causes the release of pivotal factors, e.g., histamine, MMPs, tryptase and VEGF, which are known to be involved in the attachment and posterior invasion of the embryo into the uterus. Moreover, MC degranulation correlates with angiogenesis during pregnancy. The number of MCs in the uterus has been shown to fluctuate during menstrual cycle in human and estrus cycle in rat and mouse indicating a hormonal influence on their recruitment from the periphery to the uterus. However, the mechanisms behind MC migration to the uterus are still unknown.Methodology/Principal FindingsWe first utilized migration assays to show that MCs are able to migrate to the uterus and to the fetal-maternal interface upon up-regulation of the expression of chemokine receptors by hormonal changes. By using a model of ovariectomized animals, we provide clear evidences that also in vivo, estradiol and progesterone attract MC to the uterus and further provoke their maturation and degranulation.Conclusion/SignificanceWe propose that estradiol and progesterone modulate the migration of MCs from the periphery to the uterus and their degranulation, which may prepare the uterus for implantation.

Abstract-Heme Oxygenase-1 (HO-1) and its metabolite carbon monoxide (CO) promote implantation and placentation.Pregnancy disorders such as preeclampsia and intrauterine growth restriction are linked to both HO-1 diminution and impaired remodeling of maternal spiral arteries (SAs). Here, we investigated whether CO is able to prevent preeclampsia and intrauterine growth restriction through the modulation of uterine natural killer (uNK) cells that are necessary for initiation of SA remodeling. Hmox1 +/− or Hmox1 −/− implantations presented fewer uNK cell numbers and lower expression of uNK-related angiogeneic factors compared with Hmox1 +/+ sites. Quantitative histology revealed that Hmox1 +/− and Hmox1 −/− implantations had shallow SA development that was accompanied by intrauterine growth restriction and gestational hypertension. Application of CO at low dose during early to midgestation prevented intrauterine growth restriction in Hmox1 +/− mothers, this being associated with enhanced in situ proliferation of uNK cells and normalization of angiogenic parameters. Most importantly, CO improved SA remodeling and normalized blood pressure, ensuring a proper fetal growth. Thus, CO emerges as a key molecular player in pregnancy success by modulating uNK cells, which results in promotion of SA remodeling, adequate fetal support/growth, and prevention of hypertension. Linzke et al Targeting uNK Cells to Suppress Hypertension 581 Materials and Methods AnimalsFor analysis of implantation sites, Hmox1-competent or Hmox1-deficient BALB/c mice were used. These mice were initially provided by Dr Saw Feng-Yet and bred and maintained in our facility. The progeny obtained from breeding Hmox1 +/− female animals and Hmox1 +/− male animals were genotyped and recorded. C57BL/6 male animals were obtained from Charles River (Sulzfeld, Germany). The mice were maintained in our husbandry with a 12-hour light/ dark cycle and with food and water ad libitum. All experiments were approved by German authorities (Saxony-Anhalt's Ministry 2 -868).Hmox1 For all experiments, the detection of a vaginal plug indicated day 0 of pregnancy. Animals were euthanized on days 8, 10, 12, or 18 of pregnancy. Whole implantation sites for paraffin embedding were kept in 4% paraformaldehyde with 0.1% saccharose for 6 hours. For RNA isolation, tissue of MLAp and DB was carefully washed with cold sterile PBS (pH 7.4), snap frozen, and stored at −80°C. Tissue of MLAp and DB was stored in RPMI 1640 with 10% FBS and 1% penicillin and streptomycin for flow cytometry. CO InhalationFollowing our standard protocol, Hmox1 +/+ or Hmox1 +/− female animals were exposed to CO (50 ppm) day-long from day 3 to 8 of pregnancy. 5,6 Control animals inhaled the same air mixture without CO. The exposure of animals to mixed air or CO took place in cages placed in a 98-L Plexiglas animal chamber (A-Chamber; BioSpherix, NY). Duration of exposure and dosage was previously tested and established. Both time exposure and dose prevented fetal death without any toxic side effects. 5,6 Blo...