Induction of endometriosis alters the peripheral and endometrial regulatory T cell population in the non-human primate

Non-human primate: the new frontier model of female reproductive engineering

Reproductive engineering encompasses a range of advanced tissue engineering techniques aimed at addressing infertility that is non-curable with current assisted reproductive technology (ART). The use of animal models has been crucial for these advancements, with a notable preference for non-human primates (NHPs) given their genetic, anatomical, and physiological similarities to humans. Therefore, NHPs are invaluable for studying reproductive engineering. Thus, in reproductive studies, NHPs bridge the anatomical and physiological gaps between rodent models and humans. Their shared features with humans, such as menstrual cycles, placentation, and hormonal regulation, allow for more accurate modeling of reproductive physiology and pathology. These traits make NHPs indispensable in the exploration of reproductive engineering, including infertility treatments, genetic engineering, and uterine transplantation. Reproductive engineering is a transformative field that addresses infertility and enhances reproductive health. By leveraging the unique traits of NHPs, researchers can deepen their understanding of reproductive processes and refine ART techniques for human use. Advances in genetic engineering have enabled the creation of transgenic NHP models, which have been used to modify genes to investigate roles for various purposes, and the process, as mentioned earlier, is closely related to the ART technique, including fertility, embryogenesis, and pregnancy. Therefore, the relation to reproductive studies and the necessity of the NHP model are prerequisites for reproductive engineering. The engineering of NHPs is critically related to integrating ethical practices and exploring complementary methodologies. This review overviews the types of NHP frequently used and studies using NHP for reproductive engineering. These studies may suggest a broader way to use NHP for reproductive engineering.

Influence of Hormonal Factors, Number of Sexual Partners, Surgical Intervention on Gastrointestinal and Urogenital Microbiota of Patients Endometriosis

PROBLEM

Endometriosis is associated with gastrointestinal (GI) and urogenital (UG) microbial dysbiosis in patients with endometriosis (P-EOSIS). Sexual partner exposure may contribute to microbial dysbiosis but has not been studied in P-EOSIS. We hypothesized that sexual partner number, hormonal and surgical therapy would affect GI/UG microbial dysbiosis in P-EOSIS.

METHODS OF STUDY

Urine, fecal and vaginal swabs from control (n = 15) and P-EOSIS (n = 33) were collected on the day of surgery (DOS) and ∼1-3 weeks post-surgical intervention (PSI). Control and P-EOSIS were grouped based on hormonal therapy (HT) to determine the effect of HT on microbial profiles, Control (HT n = 8; no HT n = 7) and P-EOSIS (HT n = 18; no HT n = 15). Samples underwent DNA extraction and sequencing of the V4 region of 16S rRNA gene. Sequences were processed using QIIME2 and amplicon sequence variants (ASV) were analyzed for microbial differences. Pearson's and Spearman correlation analyses determined associations among microbial features and sexual partner exposure.

RESULTS

P-EOSIS had microbial dysbiosis characterized by unique GI/UG bacteria and altered microbial richness and diversity. Hormonal and surgical intervention in P-EOSIS restored GI microbial diversity. Increased sexual partner exposure decreased GI/UG microbial diversity. P-EOSIS who had 10 or more sexual partners had greater microbial dysbiosis compared to 4-6 partners. Surgical intervention negatively correlated with sexual partner numbers and GI/UG microbial abundance.

DISCUSSION

Increased sexual partner exposure may enhance microbial dysbiosis in P-EOSIS and diminish the effectiveness of HT and surgical interventions.

Endometriosis and aspirin: a systematic review

Introduction

Endometriosis is delineated as a benign yet steroid-dependent disorder characterized by the ectopic presence of endometrial glandular and stromal cells outside the uterine cavity, affecting estimated 10%-15% of women of reproductive age, 20%-50% of all women with infertility and costing a great economic burden per-patient. Endometriosis exerts pervasive influence on multiple facets of female reproductive physiology. Given its characterization as a chronic inflammatory disorder, escalated levels of pro-inflammatory cytokines were unequivocally recognized as well-established characteristics of endometriosis, which might attribute to mechanisms like retrograde menstruation, progesterone receptor resistance, and immune dysregulation. Therapeutic utilization of non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin, analgesic agent for reducing pain, inflammation, and fever, could be holding promise in augmenting reproductive outcomes of endometriosis women. Therefore, the objective of this comprehensive review is to elucidate the intricate interplay between endometriosis and aspirin, both within the context of infertility and beyond. We meticulously explore potential pharmacological agents targeting endometriosis, which may concurrently optimize the efficacy of reproductive interventions, while also delving into the underlying mechanistic pathways linking endometriosis with inflammatory processes.

Methods

We conducted a comprehensive search in the data available in PubMed and the Web of Science using the terms 'endometriosis' and 'aspirin'. Then analyzed the identified articles based on established inclusion and exclusion criteria independently by three reviewers.

Results

The survey of the chosen terms revealed 72 articles, only 10 of which were considered for review.

Discussion

Based on the research available currently, it is not substantial enough to address the conclusion that aspirin shall be an effective therapeutic choice for endometriosis, further studies are needed to elucidate the efficacy, safety profile, and optimal dosing regimens of aspirin in the context of endometriosis treatment.

Molecular regulation of DNA damage and repair in female infertility: a systematic review

DNA damage is a key factor affecting gametogenesis and embryo development. The integrity and stability of DNA are fundamental to a woman's successful conception, embryonic development, pregnancy and the production of healthy offspring. Aging, reactive oxygen species, radiation therapy, and chemotherapy often induce oocyte DNA damage, diminished ovarian reserve, and infertility in women. With the increase of infertility population, there is an increasing need to study the relationship between infertility related diseases and DNA damage and repair. Researchers have tried various methods to reduce DNA damage in oocytes and enhance their DNA repair capabilities in an attempt to protect oocytes. In this review, we summarize recent advances in the DNA damage response mechanisms in infertility diseases such as PCOS, endometriosis, diminished ovarian reserve and hydrosalpinx, which has important implications for fertility preservation.

Potential tools for predicting response to chemotherapy in OC: Assessment of immune dysbiosis, participant's self-rated health and microbial dynamics

Epithelial ovarian cancer (OC) is the deadliest female reproductive cancer; an estimated 13,270 women will die from OC in 2023. Platinum-based chemotherapy resistance mechanisms contribute to poor OC 5-year survival rates. Peripheral inflammation is linked to various disease states and we previously identified unique peritoneal microbial features predictive of OC. We hypothesized that unique peripheral immune profiles and peritoneal microbial features may be predictive of disease-free interval (time to recurrence) and response to chemotherapy in participants with OC. We also investigated self-rated health (SRH) scores in the context of peripheral inflammation as a potential screening tool for OC. Blood and peritoneal fluid were collected from participants with OC or a benign adnexal mass (BPM). Lymphocyte populations were analyzed using Fluorescence Activated Cell Sorting, serum cytokine levels were analyzed using the Human Th17 Magnetic Bead Panel assay and peritoneal fluid microbial features were analyzed using Next Generation Sequencing (NGS). Participants completed a standardized questionnaire on self-rated physical and emotional health. Participants were classified into three chemotherapy response categories: platinum-refractory, platinum-resistant or platinum-sensitive. A significant positive correlation was found between elevated inflammatory status on the day of surgery and longer disease-free interval. SRH measures did not correlate with immune status in participants with OC or a BPM. We identified a correlation between peritoneal microbial features and chemotherapy response. We conclude that immune dysbiosis may be useful in predicting OC recurrence. The immune findings reported here set the framework for additional studies utilizing immune profiles to predict platinum-based chemotherapy responsiveness in OC.

The Known, the Unknown and the Future of the Pathophysiology of Endometriosis

Endometriosis is one of the most common causes of chronic pelvic pain and infertility, affecting 10% of women of reproductive age. A delay of up to 9 years is estimated between the onset of symptoms and the diagnosis of endometriosis. Endometriosis is currently defined as the presence of endometrial epithelial and stromal cells at ectopic sites; however, advances in research on endometriosis have some authors believing that endometriosis should be re-defined as "a fibrotic condition in which endometrial stroma and epithelium can be identified". There are several theories on the etiology of the disease, but the origin of endometriosis remains unclear. This review addresses the role of microRNAs (miRNAs), which are naturally occurring post-transcriptional regulatory molecules, in endometriotic lesion development, the inflammatory environment within the peritoneal cavity, including the role that cytokines play during the development of the disease, and how animal models have helped in our understanding of the pathology of this enigmatic disease.

Foxp3+CD39+CD73+ regulatory T-cells are decreased in the peripheral blood of women with deep infiltrating endometriosis

Endometriosis's pathophysiology remains incompletely understood, with evidence pointing towards a dysregulated immune response. Regulatory T (Treg) cells, pivotal in maintaining self-tolerance, may facilitate the survival of ectopic endometrial cells within the abdominal cavity, thereby contributing to endometriosis development. This study aimed to assess the prevalence of CD39+CD73+ suppressor Treg cell subsets in the peripheral blood of endometriosis patients. This research focuses on the pivotal role of regulatory T-cells (Tregs), which are essential for maintaining immune tolerance and preventing autoimmune diseases. A case-control study was conducted, including 32 women diagnosed with endometriosis and 22 control subjects. The frequency of peripheral blood CD39+CD73+ suppressor Treg cells was quantified using flow cytometry. No significant differences were observed in the frequency of CD3+CD4+CD25High cells (Median [M]: 10.1; Interquartile Range [IQR]: 6.32‒18.3 vs. M: 9.72; IQR: 6.22-19.8) or CD3+CD4+CD25HighCD39+Foxp3+ cells (M: 31.1; IQR: 19.7-44.0 vs. M: 30.55; IQR: 18.5-45.5) between controls and patients. However, a significantly lower frequency of CD3+CD4+CD25HighCD39+CD73+ cells was observed in the endometriosis group compared to controls (M: 1.98; IQR: 0.0377-3.17 vs. M: 2.25; IQR: 0.50-4.08; p = 0.0483), suggesting a reduction in systemic immune tolerance among these patients. This finding highlights the potential role of CD39 and CD73 expression on Treg cells as biomarkers for assessing disease severity and progression. Furthermore, elucidating the mechanisms driving these alterations may unveil new therapeutic strategies to restore immune equilibrium and mitigate endometriosis symptoms.

The role of regulatory T-cells in the development of endometriosis

Endometriosis is a benign disease of the female reproductive tract, characterized by the process of chronic inflammation and alterations in immune response. It is estimated to affect 2-19% of women in the general population and is commonly associated with symptoms of chronic pelvic pain and infertility. Regulatory T cells (Treg) are a subpopulation of T lymphocytes that are potent suppressors of inflammatory immune response, essential in preventing destructive immunity in all tissues. In endometriosis, several studies have investigated the possible role of Treg cells in the development of the disease. Most studies to date are heterogeneous in methodology and are based on a small number of cases, which means that it is impossible to define their exact role at present. Based on current knowledge, it seems that disturbed Treg homeostasis, leading to increased systemic and local inflammation within ectopic and eutopic endometrium, is present in women who eventually develop endometriosis. It is also evident that different subsets of human Treg cells have different roles in suppressing the immune response. Recent studies in patients with endometriosis have investigated naive/resting FOXP3lowCD45RA+ Treg cells, which upon T cell receptor stimulation, differentiate into activated/effector FOXP3highCD45RA- Treg cells, characterized by a strong immunosuppressive activity. In addition, critical factors controlling expression of Treg/effector genes, including reactive oxygen species and heme-responsive master transcription factor BACH2, were found to be upregulated in endometriotic lesions. As shown recently for cancer microenvironments, microbial inflammation may also contribute to the local composition of FOXP3+ subpopulations in endometriotic lesions. Furthermore, cytokines, such as IL-7, which control the homeostasis of Treg subsets through the tyrosine phosphorylation STAT5 signalling pathway, have also been shown to be dysregulated. To better understand the role of Treg in the development of endometriosis, future studies should use clear definitions of Tregs along with specific characterization of the non-Treg (FOXP3lowCD45RA-) fraction, which itself is a mixture of follicular Tregs and cells producing inflammatory cytokines.

Disrupted Tuzzerella abundance and impaired L-glutamine levels induce Treg accumulation in ovarian endometriosis: a comprehensive multi-omics analysis

INTRODUCTION

The microbial community plays a crucial role in the pathological microenvironment. However, the structure of the microbial community within endometriotic lesions and its impact on the microenvironment is still limited.

METHODS

All 55 tissue samples, including ovarian ectopic (OEMs) and normal (NE) endometrium, were subjected to 16S rRNA sequencing, metabolomic and proteomic analysis.

RESULTS

We found the abundance of Tuzzerella is significantly lower in OEMs compared to NE tissue (p < 0.01). We selected samples from these two groups that exhibited the most pronounced difference in Tuzzerella abundance for further metabolomic and proteomic analysis. Our findings indicated that endometriotic lesions were associated with a decrease in L-Glutamine levels. However, proteomic analysis revealed a significant upregulation of proteins related to the complement pathway, including C3, C7, C1S, CLU, and A2M. Subsequent metabolic and protein correlation predictions demonstrated a negative regulation between L-Glutamine and C7. In vitro experiments further confirmed that high concentrations of Glutamine significantly inhibit C7 protein expression. Additionally, immune cell infiltration analysis, multiplex immunofluorescence, and multifactorial testing demonstrated a positive correlation between C7 expression and the infiltration of regulatory T cells (Tregs) in ectopic lesions, while L-Glutamine was found to negatively regulate the expression of chemotactic factors for Tregs.

CONCLUSION

In this study, we found a clear multi-omics pathway alteration, "Tuzzerella (microbe)-L-Glutamine (metabolite)-C7 (protein)," which affects the infiltration of Tregs in endometriotic lesions. Our findings provide insights into endometriosis classification and personalized treatment strategies based on microbial structures.

Endometriosis affects the number of retrieved oocytes but not early embryonic development and live birth: a retrospective analysis of 716 IVF cycles

To investigate the potential effect of endometriosis on embryo development and clinical outcomes, a retrospective analysis of 716 women undergoing their first standard in vitro fertilization (sIVF) cycles (205 endometriosis and 511 with tubal factor infertility) was performed. The endometriosis group included women with an ultrasonographic or surgical diagnosis. Control subjects were women diagnosed with tubal factor infertility by laparoscopy or hysterosalpingogram. The primary outcome of the study was live birth. Cumulative live birth was also assessed in a subgroups analysis. After adjusting for confounders we found no significant difference in fertilization rate, blastulation, top-quality blastocyst, live birth, cumulative live birth (subgroups analysis) and miscarriage rate. In the endometriosis group, the number of retrieved oocytes was smaller (6.94 ± 4.06 Vs 7.50 ± 4.6, adjusted p < 0.05). We observed a statistically significant difference in the percentage of day-3 embryos with ≥8 blastomeres (33.12 ± 22.72 endometriosis vs, 40.77 ± 27.62 tubal factor, adjusted p < 0.01) and a negative correlation between the presence of endometriomas and a number of retrieved oocytes [B coefficient =-1.41, 95%CI (-2.31-0.51), adjusted p = 0.002]. Our results suggest that endometriosis affects the number of retrieved oocytes but not embryo development and live birth.

The deviations of CD4 + T cells during peripheral blood and peritoneal fluid of endometriosis: a systematic review and meta-analysis

OBJECTIVE

To assess whether endometriosis (EMs) was related to systematic and/or local deviations of cluster of differentiation (CD)4 + T cells.

METHODS

Until November 2022, we enrolled a total of 1363 EMs and 1564 healthy women from 32 studies who met the inclusion criteria.

RESULTS

After systematically retrieving the literature, we identified 1086 citations and 32 case-control studies were enrolled. Cumulative results suggested that there were insignificant deviations of CD4 + T cells during peripheral blood (PB) between EMs and healthy women (RR: - 0.83, I2 = 99%, p = 0.65), also no statistically significant difference was found between mild and severe EMs (RR: 3.19, I2 = 94%, p = 0.19). We also found insignificant deviations of CD4 + /CD8 + during PB between EMs and healthy women (RR: 0.09, I2 = 99%, p = 0.39), and between mild and severe EMs (RR: - 0.16, I2 = 99%, p = 0.29). The results might suggest that there was no significant correlation between EMs and systematic deviations of CD4 + T cells. When it came to local deviation during peritoneal fluid (PF), the polled results suggested that the frequency of CD4 + T cells during EMs was significantly lower than healthy women (RR: - 5.38, I2 = 93%, p = 0.01), and the ratio of CD4 + /CD8 + during EMs was significantly lower than healthy women (RR: - 0.13, I2 = 0%, p < 0.0001). However, there were insignificant deviations of CD4 + during PF between mild and severe EMs (RR: 1.65, I2 = 53%, p = 0.15), also there was an insignificant difference of CD4 + /CD8 + between mild and severe EMs (RR: - 0.09, I2 = 14%, p = 0.19). EMs might be closely related to local deviations of CD4 + T cells.

CONCLUSION

There was no obvious correlation between EMs and systematic deviations of CD4 + T cells, EMs might be closely related to local deviations of CD4 + T cells. Further study on the functional deviations and subpopulation distribution of CD4 + T cells is urgently needed.

Immunotherapy: A promising novel endometriosis therapy

Endometriosis is a common disease of the female reproductive system and has malignant features. Although endometriosis by itself is a benign disease, its erosive growth characteristics lead to severe pelvic pain and female infertility. Unfortunately, several aspects of the pathogenesis of endometriosis are still unclear. Furthermore, the clinical therapeutic methods are unsatisfactory. The recurrence rate of endometriosis is high. Accumulating evidence suggests that the onset and development of endometriosis are closely related to the abnormal function of the female autoimmune system, especially the function of some immune cells such as the aggregation of neutrophils, abnormal differentiation of macrophages, decreased cytotoxicity of NK cells, and abnormal function of T- and B-cell lines. Therefore, immunotherapy is probably a novel therapeutic strategy for endometriosis besides surgery and hormone therapy. However, information regarding the clinical application of immunotherapy in the treatment of endometriosis is very limited. This article aimed to review the effects of existing immunomodulators on the development of endometriosis, including immune cell regulators and immune factor regulators. These immunomodulators clinically or experimentally inhibit the pathogenesis and development of endometriosis lesions by acting on the immune cells, immune factors, or immune-related signaling pathways. Thus, immunotherapy is probably a novel and effective clinical treatment choice for endometriosis. Experimental studies of the detailed mechanism of immunotherapy and large-scale clinical studies about the effectiveness and safety of this promising therapeutic method are required in the future.

Immunopathogenesis of endometriosis: An overview of the role of innate and adaptive immune cells and their mediators

BACKGROUND

Endometriosis is a chronic inflammatory disease associated with the growth and proliferation of endometrial-like tissues outside the uterus. Although the exact etiology and mechanism of the pathogenesis of the disease have not been fully elucidated, the immune system cells and the mediators produced by them can be named as effective factors in the onset and progression of the disease.

AIMS

We aim to attempt to review studies on the role of the immune system in endometriosis to better understand the pathogenesis of endometriosis.

CONTENT

Abundant production of inflammatory mediators by neutrophils and macrophages and reduced cytotoxicity of defined cells promote endometriosis at the early stages of the disease. Following an increase in the inflammation of the environment, the body takes compensatory mechanisms to reduce inflammation and establish homeostasis. For this purpose, the body produces remodeling and anti-inflammatory factors leading to slow conversion of the inflammatory environment into a non-inflammatory environment with proliferative and immunosuppressive properties. Environmental conditions induce M2 macrophages, TH2 cells, and Tregs differentiation, promoting disease progression by producing angiogenic and immunosuppressive factors. However, the exact molecular mechanism involved in changing inflammatory to non-inflammatory conditions is not yet fully understood.

IMPLICATIONS

Due to the common characteristics of endometriotic cells and cancer cells, most potential treatment options for endometriosis have been suggested due to the results of these methods in the treatment of cancer. In this pathway, immune system cells and soluble mediators can be used as targets.

Effects of endometriosis on immunity and mucosal microbial community dynamics in female olive baboons

Endometriosis is defined as the growth of endometrial tissue in ectopic locations, and is associated with altered immune and microbial phenotypes. It is unclear if these changes are the result of the disease or may be causative. We induced endometriosis in non-human primates (Papio Anubis) to test our hypothesis that the growth of endometriotic lesions results in alterations in immune and microbial dynamics that may advance disease progression. Baboon samples were collected pre-inoculation (prior to disease induction), at 3, 6, 9, and 15 months after disease induction. Tolerant regulatory T-cells (Tregs) and inflammatory T-helper 17 (Th17) cells were identified in peripheral blood and within the eutopic/ectopic endometrial tissues. Microbiome communities were identified in fecal/urine samples. The induction of endometriosis decreased peripheral Tregs cells while Th17 cells increased at all post-induction collections, thus reducing the Tregs:Th17 cells ratio, indicating systemic inflammation. Microbiome diversity and abundance were altered at each sample site after disease induction. Thus, induction of endometriosis in baboons caused an immune shift toward an inflammatory profile and altered mucosal microbial profiles, which may drive inflammation through production of inflammatory mediators. Immune and microbial profiling may lead to innovative diagnostic tools and novel therapies for endometriosis treatment.

Placenta Previa Complicated with Endometriosis: Contemporary Clinical Management, Molecular Mechanisms, and Future Research Opportunities

Endometriosis is a common gynecological disease characterized by chronic inflammation, with an estimated prevalence of approximately 5–15% in reproductive-aged women. This study aimed to assess the relationship between placenta previa (PP) and endometriosis. We performed a systematic review of the literature until 30 June 2021, and 24 studies met the inclusion criteria. Using an adjusted pooled analysis, we found that women with endometriosis had a significantly increased rate of PP (adjusted odds ratio (OR) 3.17, 95% confidence interval (CI) 2.58–3.89) compared to those without endometriosis. In an unadjusted analysis, severe endometriosis was associated with an increased prevalence of PP (OR 11.86, 95% CI 4.32–32.57), whereas non-severe endometriosis was not (OR 2.16, 95% CI 0.95–4.89). Notably, one study showed that PP with endometriosis was associated with increased intraoperative bleeding (1.515 mL versus 870 mL, p < 0.01) compared to those without endometriosis. Unfortunately, no studies assessed the molecular mechanisms underlying PP in patients with endometriosis. Our findings suggest that there is a strong association between endometriosis and a higher incidence of PP, as well as poor surgical outcomes during cesarean delivery. Therefore, the development of novel therapeutic agents or methods is warranted to prevent PP in women with endometriosis.

Endometriotic Peritoneal Fluid Stimulates Recruitment of CD4+CD25highFOXP3+ Treg Cells

Endometriosis is a common gynecological disorder characterized by the presence of endometrial-like tissue outside the uterus. The disease is associated with disturbed local and systemic immunity. It has been reported that the proportion of CD4⁺CD25^highFOXP3⁺ Treg cells may be significantly increased in the peritoneal fluid of patients with endometriosis. Therefore, the aim of our study was to investigate whether the proportions of Treg cells in the peritoneal cavity of patients with endometriosis are related to the chemotactic and stimulatory activity of the local peritoneal milieu. The peritoneal fluid was collected from 13 women with ovarian endometriosis and 12 control women without the disease. T cell populations were analyzed by flow cytometry, cytokines and chemokines were evaluated using the cytometric bead kit, and cell chemotaxis was studied by cell migration assay. We confirmed that the proportions of Treg cells are increased in the peritoneal fluid of women with endometriosis as compared to the control women. Endometriosis was also associated with elevated concentrations of IL-6, IL-10, and TGF-β1/2 as well as CCL20, CXCL8, CXCL9, and CXCL10. We did not reveal any changes in the proportion of peritoneal Th17 cells and concentrations of IL-17A. Peritoneal Treg cells positively correlated with concentrations of TGF-β, IL-10, and CCL20. Endometriotic peritoneal fluid stimulated chemotaxis of both CD4⁺ and Treg cells. This chemotactic activity positively correlated with concentrations of CCL20. CCL20 stimulated the migration of Treg cells, and the chemotactic activity of the endometriotic peritoneal fluid was inhibited by neutralizing anti-CCL20 antibodies. These results imply that increased proportions of the peritoneal Treg cells in women with endometriosis may result from attraction and activation by local chemokines and cytokines, especially CCL20 and TGF-β. Since Treg cells contribute to the immunopathogenesis of endometriosis, their chemotaxis and activation may be considered as a target for therapeutic intervention.

Peritoneal Fluid from Patients with Ovarian Endometriosis Displays Immunosuppressive Potential and Stimulates Th2 Response

Endometriosis is a common gynaecological disorder characterized by the ectopic growth of endometrial tissue outside the uterine cavity. It is associated with chronic pelvic inflammation and autoimmune reactivity manifesting by autoantibody production and abrogated cellular immune responses. Endometriotic peritoneal fluid contains various infiltrating leucocyte populations and a bulk of proinflammatory and immunoregulatory cytokines. However, the nature and significance of the peritoneal milieu in women with endometriosis still remains obscure. Therefore, the aim of the present study was to investigate the immunoregulatory activity of the peritoneal fluid (PF) from women with endometriosis. The peritoneal fluid samples were collected during laparoscopic surgery from 30 women with and without endometriosis. Immunoregulatory cytokines (IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-γ and TNF) and chemokines (CCL2, CCL5, CXCL8 and CXCL9) were evaluated in PF and culture supernatants generated by unstimulated and CD3/CD28/IL-2-stimulated CD4⁺ T cells cultured in the presence of PF. The effect of PF on the generation of Treg and Th17 cells in CD4⁺ T cell cultures, as well as the natural cytotoxic activity of peripheral blood mononuclear cells, was also investigated. Concentrations of IL-6, IL-10, CCL2, CXCL8 and CXCL9 were significantly upregulated in the PF from women with endometriosis when compared to control women, whereas concentrations of other cytokines and chemokines were unaffected. The culturing of unstimulated and CD3/CD28/IL-2-stimulated CD4⁺ T cells in the presence of endometriotic PF resulted in the downregulation of their IL-2, IFN-γ, IL-17A and TNF production as compared to culture medium alone. On the other side, endometriotic PF significantly stimulated the production of IL-4 and IL-10. Endometriotic PF also stimulated the release of CCL2 and CXCL8, whereas the production of CCL5 and CXCL9 was downregulated. Endometriotic PF stimulated the generation of Treg cells and had an inhibitory effect on the generation of Th17 cells in cultures of CD4⁺ T cells. It also inhibited the NK cell cytotoxic activity of the peripheral blood lymphocytes. These results strongly imply that the PF from patients with endometriosis has immunoregulatory/immunosuppressive activity and shifts the Th1/Th2 cytokine balance toward the Th2 response, which may account for deviation of local and systemic immune responses. However, a similar trend, albeit not a statistically significant one, was also observed in case of PF from women without endometriosis, thus suggesting that peritoneal milieu may in general display some immunoregulatory/immunosuppressive properties. It should be stressed, however, that our present observations were made on a relatively small number of PF samples and further studies are needed to reveal possible mechanism(s) responsible for this phenomenon.

Clinical consequences of defective decidualization

Decidualization is characterized by a series of genetic, metabolic, morphological, biochemical, vascular and immune changes occurring in the endometrial stroma in response to the implanting embryo or even before conception and involves the stromal cells of the endometrium. It is a fundamental reproductive event occurring in mammalian species with hemochorial placentation. A growing body of experimental and clinical evidence strongly suggests that defective or disrupted decidualization contributes to the establishment of an inappropriate maternal-fetal interface. This has relevant clinical consequences, ranging from recurrent implantation failure and recurrent pregnancy loss in early pregnancy to several significant complications of advanced gestation. Moreover, recent evidence indicates that selected diseases of the endometrium, such as chronic endometritis and endometriosis, can have a detrimental impact on the decidualization response in the endometrium and may help explain some aspects of the reduced reproductive outcome associated with these conditions. Further research efforts are needed to fully understand the biomolecular mechanisms ans events underlying an abnormal decidualization response. This will permit the development of new diagnostic and therapeutic strategies aimed to improve the likelihood of achieveing a successful pregnancy.

THE EFFECTS OF ETANERCEPT AND CABERGOLINE ON ENDOMETRIOTIC IMPLANTS, UTERUS AND OVARIES IN RAT ENDOMETRIOSIS MODEL

The pathophysiology of endometriosis is still unknown and treatment options remain controversial. Searches focus on angiogenesis, stem cells, immunologic and inflammatory factors. This study investigated the effects of etanercept and cabergoline on ovaries, ectopic, and eutopic endometrium in an endometriosis rat model. This randomized, placebo-controlled, blinded study included 50 rats, Co(control), Sh(Sham), Cb(cabergoline), E(etanercept), and E + Cb(etanercept + cabergoline) groups. After surgical induction of endometriosis, 2^nd operation was performed for endometriotic volume and AMH level. After 15 days of treatment: AMH level, flow cytometry, implant volume, histologic scores, immunohistochemical staining of ectopic, eutopic endometrium, and ovary were evaluated at 3^rd operation. All groups had significantly reduced volume, TNF-α, VEGF, and CD 146/PDGF-Rβ staining of endometriotic implants comparing to the Sh group (p < 0.05).TNF-α staining of eutopic endometrium in all treatment groups was similar to Sh and Co groups (p > 0.05). E and E + Cb groups significantly decreased TNF-α staining in the ovary comparing to Sh, Co, and Cb groups (p < 0.05). All treatment groups had significantly higher AFC compared to the Sh group. CD25⁺ Cells' median percentage was significantly increased in the E + Cb group compared to Co, Sh, Cb, and E group. E + Cb group had a significantly higher CD5⁺ Cells' level than the Co group (p = 0.035). In conclusion; Etanercept and/or Cabergoline decreased volume, TNF-α, VEGF, and CD 146/PDGF-Rβ staining of the ectopic endometrial implant. E and E + Cb treatment decreased TNF-α levels in the ovary. E + Cb also increased peripheral blood CD25⁺ & CD5⁺ Cell's.

Effect of Human Chorionic Gonadotropin Injection Before Frozen Embryo Transfer on Pregnancy Outcomes in Endometriosis-Associated Infertility

Purpose: The aim of this study was to investigate the effect of human chorionic gonadotropin (hCG) in hormone replacement (HT) regime for frozen thawed embryo transfer in women with endometriosis (EM). Methods: We performed a retrospective, database-search, cohort study and included data on EM patients who underwent frozen embryo transfer (FET) between January 1, 2009 and August 31, 2018. According to the protocols for FET cycle, the patients were divided into two groups: control group (n = 296) and hCG group (n = 355). Clinical pregnancy rate, live birth rate, early abortion rate, late abortion rate, and ectopic pregnancy rate were compared between the two groups. Results: There was a significant increase in clinical pregnancy rate in the hCG group (57.7 vs. 49%, p = 0.027) compared with the control group. The live birth rate in the hCG group (45.6 vs. 38.5%, p = 0.080) was also elevated, but this difference was not statistically significant. Conclusion: hCG administration in HT regime for FET increases the pregnancy rate in women with EM.

Alteration of systemic and uterine endometrial immune populations in patients with endometriosis

PROBLEM

Endometriosis is defined as growth of endometrial tissue in ectopic locations; it is associated with infertility and chronic pain and affects ~12% of reproductive-aged women. Although inflammation is known to play a key role in endometriosis, knowledge related to immune phenotypes associated with this disease is lacking. This study aimed to characterize immune profiles in patients with endometriosis, to assess inflammatory mediators, to and determine if surgical and/or hormonal therapies restore immune homeostasis.

METHODS OF STUDY

Samples from nine controls and 20 histologically confirmed endometriosis patients were collected upon surgery and ~1-3 weeks post-surgical intervention. Subjects were either not utilizing hormonal suppression or were currently on monophasic hormonal therapy. Tolerant regulatory T cells (Tregs = natural [nTregs] +inducible [iTregs]) and inflammatory T helper 17 (Th17) cells were identified in peripheral blood via flow cytometry and within the eutopic/ectopic endometrial tissues via immunohistochemistry and real-time-qPCR. Cytokines were assessed via 10-plex-ELISA.

RESULTS

Patients with endometriosis not utilizing hormonal therapy exhibited lower iTregs (tolerant), greater Th17 (inflammatory), and a reduction in Treg/Th17 ratio (P < .05), indicative of systemic inflammation. Treg and Th17 localizations were enhanced within the ectopic endometrial implant, which promotes lesion development. Hormonal therapy decreased systemic and local inflammation (eutopic/ectopic endometrium) via decreased iTregs and Th17 cells in patients with endometriosis (P < .05). Thus, imbalance within immune populations correlated with increased inflammation in patients with endometriosis, which was mitigated by hormonal therapy.

CONCLUSIONS

Patients with endometriosis exhibited systemic and localized inflammation within ectopic and endometrial tissues. Hormonal therapy dampened inflammation caused by disease.

CD200 and CD200R Expression on Peripheral Blood Lymphocytes and Serum CD200 Concentration as a New Marker of Endometriosis

The causes of endometriosis (EMS) remain unknown; however, a number of immunological abnormalities contribute to the pathogenesis of the disease. The cluster of differentiation-200 (CD200) and its receptor (CD200R) maintain peripheral self-tolerance by negatively regulating immune responses. In this comparative cross-sectional study, we investigated the expression of CD200 and CD200R on T and B lymphocytes and the serum level of soluble CD200 (sCD200) using flow cytometry and ELISA, respectively. Peripheral blood samples were collected from 54 female patients and 20 healthy, age-matched controls. Results were tested for correlation with disease severity and selected clinical parameters. We demonstrated that the differences in sCD200 levels (p = 0.001), the frequencies of CD200-positive T and B lymphocytes (p < 0.001 and p = 0.004, respectively), and the frequencies of CD200R-positive T and B lymphocytes (p < 0.001 for all comparisons) in the study group correlated positively with disease severity. Receiver operating characteristic (ROC) analysis indicated that aberrant expression of CD200/CD200R might serve as a marker to distinguish between EMS cases. Finally, negative co-stimulatory factors may contribute to the induction and persistence of inflammation associated with EMS. It seems that it is essential to determine whether alteration in the CD200/CD200R pathway can be therapeutically targeted in EMS.

Role of Regulatory T Cells in Regulating Fetal-Maternal Immune Tolerance in Healthy Pregnancies and Reproductive Diseases

Regulatory T cells (Tregs) are a specialized subset of T lymphocytes that function as suppressive immune cells and inhibit various elements of immune response in vitro and in vivo. While there are constraints on the number or function of Tregs which can be exploited to evoke an effective anti-tumor response, sufficient expansion of Tregs is essential for successful organ transplantation and for promoting tolerance of self and foreign antigens. The immune-suppressive property of Tregs equips this T lymphocyte subpopulation with a pivotal role in the establishment and maintenance of maternal tolerance to fetal alloantigens, which is necessary for successful pregnancy. Elevation in the level of pregnancy-related hormones including estrogen, progesterone and human chorionic gonadotropin promotes the recruitment and expansion of Tregs, directly implicating these cells in the regulation of fetal-maternal immune tolerance. Current studies have provided evidence that a defect in the number or function of Tregs contributes to the etiology of several reproductive diseases, such as recurrent spontaneous abortion, endometriosis, and pre-eclampsia. In this review, we provide insight into the underlying mechanism through which Tregs contribute to pregnancy-related immune tolerance and demonstrate the association between deficiencies in Tregs and the development of reproductive diseases.

Regulatory T cells in embryo implantation and the immune response to pregnancy

At implantation, the embryo expresses paternally derived alloantigens and evokes inflammation that can threaten reproductive success. To ensure a robust placenta and sustainable pregnancy, an active state of maternal immune tolerance mediated by CD4+ regulatory T cells (Tregs) is essential. Tregs operate to inhibit effector immunity, contain inflammation, and support maternal vascular adaptations, thereby facilitating trophoblast invasion and placental access to the maternal blood supply. Insufficient Treg numbers or inadequate functional competence are implicated in idiopathic infertility and recurrent miscarriage as well as later-onset pregnancy complications stemming from placental insufficiency, including preeclampsia and fetal growth restriction. In this Review, we summarize the mechanisms acting in the conception environment to drive the Treg response and discuss prospects for targeting the T cell compartment to alleviate immune-based reproductive disorders.

The Immunopathophysiology of Endometriosis

Endometriosis is a chronic, inflammatory, estrogen-dependent disease characterized by the growth of endometrial tissue outside of the uterine cavity. Although the etiology of endometriosis remains elusive, immunological dysfunction has been proposed as a critical facilitator of ectopic lesion growth following retrograde menstruation of endometrial debris. However, it is not clear whether this immune dysfunction is a cause or consequence of endometriosis. Thus, here we provide in-depth insights into our current understanding of the immunopathophysiology of endometriosis and highlight challenges and opportunities for future research. With the explosion of successful immune-based therapies targeting various chronic inflammatory conditions, it is crucial to determine whether immune dysfunction can be therapeutically targeted in endometriosis.

Animal models of endometriosis: Replicating the aetiology and symptoms of the human disorder

Endometriosis is a chronic incurable disorder that affects 1 in 10 women of reproductive age: associated symptoms include chronic pain and infertility. The aetiology of endometriosis remains poorly understood but patients, clinicians and researchers are all in agreement that new non-surgical therapies are urgently needed to reduce the severity of symptoms. Preclinical testing of drugs requires the development and validation of models that recapitulate the key features of the disorder. In this review we describe the best-validated animal models (primate, rodent, xenograft) and their contributions to our understanding of the factors underpinning the development of symptoms. We consider the evidence that these models have provided the platform for identification of new therapeutic interventions and reflect on future directions for research and drug validation.

Implications of immune dysfunction on endometriosis associated infertility

Endometriosis is a complex, inflammatory disease that affects 6-10% of reproductive-aged women. Almost half of the women with endometriosis experience infertility. Despite the excessive prevalence, the pathogenesis of endometriosis and its associated infertility is unknown and a cure is not available. While many theories have been suggested to link endometriosis and infertility, a consensus among investigators has not emerged. In this extensive review of the literature as well as research from our laboratory, we provide potential insights into the role of immune dysfunction in endometriosis associated infertility. We discuss the implication of the peritoneal inflammatory microenvironment on various factors that contribute to infertility such as hormonal imbalance, oxidative stress and how these could further lead to poor oocyte, sperm and embryo quality, impaired receptivity of the endometrium and implantation failure.

Suppressive regulatory T cells and latent transforming growth factor-β-expressing macrophages are altered in the peritoneal fluid of patients with endometriosis

BACKGROUND

Endometriosis is a known cause of infertility. Differences in immune tolerance caused by regulatory T cells (Tregs) and transforming growth factor-β (TGF-β) are thought to be involved in the pathology of endometriosis. Evidence has indicated that Tregs can be separated into three functionally and phenotypically distinct subpopulations and that activated TGF-β is released from latency-associated peptide (LAP) on the surfaces of specific cells. The aim of this study was to examine differences in Treg subpopulations and LAP in the peripheral blood (PB) and peritoneal fluid (PF) of patients with and without endometriosis.

METHODS

PB and PF were collected from 28 women with laparoscopically and histopathologically diagnosed endometriosis and 20 disease-free women who were subjected to laparoscopic surgery. Three subpopulations of CD4⁺ T lymphocytes (CD45RA⁺FoxP3^low resting Tregs, CD45RA^-FoxP3^high effector Tregs, and CD45RA^-FoxP3^low non-Tregs) and CD11b⁺ mononuclear cells expressing LAP were analyzed by flow cytometry using specific monoclonal antibodies.

RESULTS

Proportions of suppressive Tregs (resting and effector Tregs) were significantly higher in the PF samples of patients with endometriosis than in those of control women (P = 0.02 and P < 0.01, respectively) but did not differ between the PB samples of patients and controls. The percentage of CD11b⁺LAP⁺ macrophages was significantly lower in PF samples of patients with endometriosis than in those of controls (P < 0.01) but was not altered in the PB samples.

CONCLUSION

Proportions of suppressive Tregs and LAP⁺ macrophages are altered locally in the PF of endometriosis patients.

Nonhuman Primates: A Vital Model for Basic and Applied Research on Female Reproduction, Prenatal Development, and Women's Health

The comparative biology of reproduction and development in mammalian species is remarkable. Hence, because of similarities in environmental and neuroendocrine control of the reproductive axis, the cyclic function of the ovary and reproductive tract, establishment and control of the maternal-fetal-placental unit during pregnancy, and reproductive aging from puberty through menopause, nonhuman primates (NHPs) are valuable models for research related to women's reproductive health and its disorders. This chapter provides examples of research over the past 10+ years using Old World monkeys (notably macaque species), baboons, and to a lesser extent New World monkeys (especially marmosets) that contributed to our understanding of the etiology and therapies or prevention of: (1) ovarian disorders, e.g., polycystic ovary syndrome, mitochondrial DNA-based diseases from the oocyte; (2) uterine disorders, for example, endometriosis and uterine transplantation; and (3) pregnancy disorders, for example, preterm labor and delivery, environmental factors. Also, emerging opportunities such as viral (e.g., Zika) induced fetal defects and germline genomic editing to generate valuable primate models of human diseases (e.g., Huntington and muscular dystrophy) are addressed. Although the high costs, specialized resources, and ethical debate challenge the use of primates in biomedical research, their inclusion in fertility and infertility research is vital for continued improvements in women's reproductive health.

Endometrial receptivity in the eutopic endometrium of women with endometriosis: it is affected, and let me show you why

The endometrium maintains complex controls on proliferation and apoptosis as part of repetitive menstrual cycles that prepare the endometrium for the window of implantation and pregnancy. The reliance on inflammatory mechanisms for both implantation and menstruation creates the opportunity in the setting of endometriosis for establishment of chronic inflammation that is disruptive to endometrial receptivity, causing both infertility and abnormal bleeding. Clinically, there can be little doubt that the endometrium of women with endometriosis is less receptive to embryo implantation, and strong evidence exists to suggest that endometrial changes are associated with decreased cycle fecundity as a result of this disease. Here we provide unifying concepts regarding those changes and how they are coordinated to promote progesterone resistance and estrogen dominance through aberrant cell signaling pathways and reduced expression of key homeostatic proteins in eutopic endometrium of women with endometriosis.

Uterine Leukocyte Function and Dysfunction: A Hypothesis on the Impact of Endometriosis

Endometriosis is a chronic inflammatory disease characterized by the growth of endometrial glands and stroma outside of the uterus. The disease affects approximately 10-15% of women of reproductive age and presents with clinical symptoms of pelvic pain and infertility. Changes in the leukocyte populations within the ectopic tissue and eutopic endometrium have been reported, and data suggest these alterations contribute to the pathology and symptoms of the disease. In this review, we discussed differences when comparing uterine NK cells and regulatory T cells within the eutopic endometrium between patients with endometriosis and healthy patients, and how these differences relate to implantation failure and/or decreased clearance of menstrual tissue in patients with the disease. The data demonstrate a critical need to examine endometrium and menstrual tissue in patients with endometriosis excluded from studies examining unknown causes of infertility and heavy menstrual bleeding. The information gathered from excluded patients will further enhance our understanding of how the immune system contributes to the pathophysiology of endometriosis and help to identify biomarkers for patients at higher risk for developing endometriosis-associated infertility.

A current view of the role of epigenetic changes in the aetiopathogenesis of endometriosis

The purpose of the study was to examine the role of epigenetic changes in the aetiopathogenesis of endometriosis. The analysis and review of the relevant current literature in English language related to the role of epigenetic changes in the aetiopathogenesis of endometriosis. Epigenetic changes are common denominators for hormonal, immunological and inflammatory aberrations which play a key role in the aetiopathogenesis of endometriosis. Many internal and external factors may cause the different running of the epigenetic mechanism. As yet fully unknown genetic factors may increase the sensitivity of the epigenetic mechanism to various internal and external factors. The breakdown of epigenetic regulation is the main factor initiating the pathogenetic mechanisms for endometriosis formation.

Endometriosis-induced changes in regulatory T cells - insights towards developing permanent contraception

BACKGROUND

Endometriosis is a gynecological disorder that is associated with alterations in the immune system that contributes to its pathology as well as its associated infertility.

MAIN FINDINGS

This brief report summarizes our findings related to the changes in T regulatory cells (Tregs) that may affect the uterine environment and impact the fertility of women and nonhuman primates with endometriosis.

PRINCIPAL CONCLUSION

Targeted therapies that could reduce Tregs within the reproductive tract may have a potential as long-lasting or permanent contraception.

Menstrual blood-derived stromal stem cells from women with and without endometriosis reveal different phenotypic and functional characteristics

Retrograde flow of menstrual blood cells during menstruation is considered as the dominant theory for the development of endometriosis. Moreover, current evidence suggests that endometrial-derived stem cells are key players in the pathogenesis of endometriosis. In particular, endometrial stromal stem cells have been suggested to be involved in the pathogenesis of this disease. Here, we aimed to use menstrual blood, as a novel source of endometrial stem cells, to investigate whether stromal stem cells from endometriosis (E-MenSCs) and non-endometriosis (NE-MenSCs) women differed regarding their morphology, CD marker expression pattern, proliferation, invasion and adhesion capacities and their ability to express certain immunomodulatory molecules. E-MenSCs were morphologically different from NE-MenSCs and showed higher expression of CD9, CD10 and CD29. Furthermore, E-MenSCs had higher proliferation and invasion potentials compared with NE-MenSCs. The amount of indoleamine 2,3-dioxygenase-1 (IDO1) and cyclooxygenase-2 (COX-2) in E-MenSCs co-cultured with allogenic peripheral blood mononuclear cells (PBMCs) was shown to be higher both at the gene and protein levels, and higher IDO1 activity was detected in the endometriosis group. However, NE-MenSCs revealed increased concentrations of forkhead transcription factor-3 (FOXP3) when compared with E-MenSCs. Nonetheless, interferon (IFN)-γ, Interleukin (IL)-10 and monocyte chemoattractant protein-1 (MCP-1) levels were higher in the supernatant of E-MenSCs-PBMC co-cultures. Here, we showed that there are inherent differences between E-MenSCs and NE-MenSCs. These findings propose the key role MenSCs could play in the pathogenesis of endometriosis and further support the retrograde and stem cell theories of endometriosis. Hence, considering its renewable and easily available nature, menstrual blood could be viewed as a reliable and inexpensive material for studies addressing the cellular and molecular aspects of endometriosis.

Effects of IL8 and immune cells on the regulation of luteal progesterone secretion

Recent studies have suggested that chemokines may mediate the luteolytic action of prostaglandin F2α (PGF). Our objective was to identify chemokines induced by PGF in vivo and to determine the effects of interleukin 8 (IL8) on specific luteal cell types in vitro. Mid-cycle cows were injected with saline or PGF, ovaries were removed after 0.5-4 h, and expression of chemokine was analyzed by qPCR. In vitro expression of IL8 was analyzed after PGF administration and with cell signaling inhibitors to determine the mechanism of PGF-induced chemokine expression. Purified neutrophils were analyzed for migration and activation in response to IL8 and PGF. Purified luteal cell types (steroidogenic, endothelial, and fibroblast cells) were used to identify which cells respond to chemokines. Neutrophils and peripheral blood mononuclear cells (PBMCs) were cocultured with steroidogenic cells to determine their effect on progesterone production. IL8, CXCL2, CCL2, and CCL8 transcripts were rapidly increased following PGF treatment in vivo. The stimulatory action of PGF on IL8 mRNA expression in vitro was prevented by inhibition of p38 and JNK signaling. IL8, but not PGF, TNF, or TGFB1, stimulated neutrophil migration. IL8 had no apparent action in purified luteal steroidogenic, endothelial, or fibroblast cells, but stimulated ERK phosphorylation in neutrophils. In coculture experiments neither IL8 nor activated neutrophils altered basal or LH-stimulated luteal cell progesterone synthesis. In contrast, activated PBMCs inhibited LH-stimulated progesterone synthesis from cultured luteal cells. These data implicate a complex cascade of events during luteolysis, involving chemokine signaling, neutrophil recruitment, and immune cell action within the corpus luteum.

Seminal fluid and the generation of regulatory T cells for embryo implantation

T regulatory (Treg) cells are essential mediators of the maternal immune adaptation necessary for embryo implantation. In mice, insufficient Treg cell activity results in implantation failure, or constrains placental function and fetal growth. In women, Treg cell deficiency is linked with unexplained infertility, miscarriage, and pre-eclampsia. To devise strategies to improve Treg cell function, it is essential to define the origin of the Treg cells in gestational tissues, and the regulators that control their functional competence and recruitment. Male seminal fluid is a potent source of the Treg cell-inducing agents TGFβ and prostaglandin E, and coitus is one key factor involved in expanding the pool of inducible Treg cells that react with paternal alloantigens shared by conceptus tissues. In mice, coitus initiates a sequence of events whereby female dendritic cells cross-present seminal fluid antigens and activate T cells, which in turn circulate via the blood to be sequestered into the endometrium. Similar events may occur in the human genital tract, where seminal fluid induces immune cell changes that appear competent to prime Treg cells. Improved understanding of how seminal fluid influences Treg cells in women should ultimately assist in the development of new therapies for immune-mediated pathologies of pregnancy.

Control of uterine microenvironment by foxp3(+) cells facilitates embryo implantation

Implantation of the fertilized egg into the maternal uterus depends on the fine balance between inflammatory and anti-inflammatory processes. Whilst regulatory T cells (Tregs) are reportedly involved in protection of allogeneic fetuses against rejection by the maternal immune system, their role for pregnancy to establish, e.g., blastocyst implantation, is not clear. By using 2-photon imaging we show that Foxp3(+) cells accumulated in the mouse uterus during the receptive phase of the estrus cycle. Seminal fluid further fostered Treg expansion. Depletion of Tregs in two Foxp3.DTR-based models prior to pairing drastically impaired implantation and resulted in infiltration of activated T effector cells as well as in uterine inflammation and fibrosis in both allogeneic and syngeneic mating combinations. Genetic deletion of the homing receptor CCR7 interfered with accumulation of Tregs in the uterus and implantation indicating that homing of Tregs to the uterus was mediated by CCR7. Our results demonstrate that Tregs play a critical role in embryo implantation by preventing the development of a hostile uterine microenvironment.