The importance of the macrophage within the human endometrium

The physiological role of macrophages in reproductive organs

Background

Macrophages are essential immune cells critical to reproductive physiology. They regulate key processes such as follicular development, ovulation, and luteinization in the ovaries. Macrophages are also involved in endometrial remodeling, immune tolerance, and placentation in the uterus.

Methods

This review examined the biological characteristics of macrophages and their role in ovarian, uterine, and fallopian tube physiology. It focused on findings from both animal and human studies to provide a comprehensive understanding of macrophage functions.

Main Findings

In the ovaries, M1 macrophages play a role in folliculogenesis and ovulation through the inflammatory and angiogenic pathways. Macrophages also maintain the corpus luteum and vascular integrity. In the uterus, macrophages regulate tissue repair and remodeling during the menstrual cycle and play a critical role in implantation by maintaining immune tolerance and supporting decidualization. Dysregulation of the M1/M2 balance can cause implantation failure. In the fallopian tubes, macrophages mediate tissue repair and immune responses. Macrophage polarization dynamically adapts to physiological and pathological conditions in all reproductive organs highlighting the functional plasticity of these cells.

Conclusion

Macrophage polarization and functions are pivotal in maintaining reproductive health. Hence, understanding the role of macrophages in various reproductive organs provides a foundation for developing new therapies.

Mechanism of Endometrial Receptivity Affected by Fibroids

Fibroids are the most common benign tumors of the female reproductive system. Most patients with fibroids are asymptomatic, but the presence of fibroids can still cause some abnormal clinical symptoms, such as increased menstrual volume, abnormal uterine bleeding, pelvic pain, urinary tract and gastrointestinal tract compression symptoms, etc. The impact of fibroids on pregnancy is worth discussing. At present, it is believed that submucosal myoma and intramural myoma affecting uterine cavity shape affect the pregnancy outcome of patients, while the impact of type III intramural myoma on pregnancy is still controversial. A number of studies have found that in addition to direct contact with the endometrial compression, uterine myoma also affects the endometrial flexibility through other ways. In this review, we summarized the effects of fibroids on endometrial receptivity and discussed in depth the mechanisms of such effects, including secretion of cytokines, changes in endometrial blood flow and angiogenesis, effects on endometrial peristalsis and mechanical stress conduction, changes in uterine microecological environment, and abnormal signal transduction pathways. Understanding the mechanism of endometrial receptivity affected by fibroids is significant for exploring the treatment of fibroids, improving the pregnancy outcome of patients with fibroids and increasing the clinical pregnancy rate.

Mechanistic insights into intrauterine adhesions

Intrauterine adhesions (IUA), also known as Asherman's syndrome, arise from damage to the basal layer of the endometrium, frequently caused by intrauterine interventions. This damage leads to nonregenerative healing of endometrium resulting in replacement by fibrous connective tissue, which bring about the adherence of opposing endometrium to render the uterine cavity and/or cervical canal partially or completely obliterated. IUA is a common cause of the refractory uterine infertility. Hysteroscopy is the gold standard for diagnosis of IUA. However, the method of accurately predicting the likelihood of achieving a live birth in the future remains established. Classical treatments have shown limited success, particularly in severe cases. Therefore, utilizing new research methods to deepen the understanding of the pathogenesis of IUA will facilitate the new treatment approaches to be found. In this article we briefly described the advances in the pathogenesis of IUA, with focus on inflammation and parenchymal cellular homeostasis disruption, defects in autophagy and the role of ferroptosis, and we also outlined the progress in IUA therapy.

Activated THP-1 Macrophage-Derived Factors Increase the Cytokine, Fractalkine, and EGF Secretions, the Invasion-Related MMP Production, and Antioxidant Activity of HEC-1A Endometrium Cells

Endometrium receptivity is a multifactor-regulated process involving progesterone receptor-regulated signaling, cytokines and chemokines, and additional growth regulatory factors. In the female reproductive system, macrophages have distinct roles in the regulation of receptivity, embryo implantation, immune tolerance, and angiogenesis or oxidative stress. In the present study, we investigated the effects of PMA-activated THP-1 macrophages on the receptivity-related genes, cytokines and chemokines, growth regulators, and oxidative stress-related molecules of HEC-1A endometrium cells. We established a non-contact co-culture in which the culture medium of the PMA-activated macrophages exhibiting the pro-inflammatory phenotype was used for the treatment of the endometrial cells. In the endometrium cells, the expression of the growth-related factors activin and bone morphogenetic protein 2, the growth hormone EGF, and the activation of the downstream signaling molecules pERK1/2 and pAkt were analyzed by ELISA and Western blot. The secretions of cytokines and chemokines, which are involved in the establishment of endometrial receptivity, and the expression of matrix metalloproteinases implicated in invasion were also determined. Based on the results, the PMA-activated THP-1 macrophages exhibiting a pro-inflammatory phenotype may play a role in the regulation of HEC-1A endometrium cells. They alter the secretion of cytokines and chemokines, as well as the protein level of MMPs of HEC-1A cells. Moreover, activated THP-1 macrophages may elevate oxidative stress protection of HEC-1A endometrium cells. All these suggest that pro-inflammatory macrophages have a special role in the regulation of receptivity-related and implantation-related factors of HEC-1A cells.

An integrated single-cell reference atlas of the human endometrium

The complex and dynamic cellular composition of the human endometrium remains poorly understood. Previous endometrial single-cell atlases profiled few donors and lacked consensus in defining cell types. We introduce the Human Endometrial Cell Atlas (HECA), a high-resolution single-cell reference atlas (313,527 cells) combining published and new endometrial single-cell transcriptomics datasets of 63 women with and without endometriosis. HECA assigns consensus and identifies previously unreported cell types, mapped in situ using spatial transcriptomics and validated using a new independent single-nuclei dataset (312,246 nuclei, 63 donors). In the functionalis, we identify intricate stromal-epithelial cell coordination via transforming growth factor beta (TGFβ) signaling. In the basalis, we define signaling between fibroblasts and an epithelial population expressing progenitor markers. Integration of HECA with large-scale endometriosis genome-wide association study data pinpoints decidualized stromal cells and macrophages as most likely dysregulated in endometriosis. The HECA is a valuable resource for studying endometrial physiology and disorders, and for guiding microphysiological in vitro systems development.

Amphiregulin secreted by umbilical cord multipotent stromal cells protects against ferroptosis of macrophages via the activating transcription factor 3-CD36 axis to alleviate endometrial fibrosis

Endometrium fibrosis is the leading cause of uterine infertility. Macrophages participated in the occurrence and development of endometrial fibrosis. We previously reported that human umbilical cord multipotent stromal cells (hUC-MSCs) exerted their therapeutic effect in a macrophage-dependent manner in endometrial fibrosis. However precise mechanisms by which hUC-MSCs may influence macrophages in endometrial fibrosis remain largely unexplored. Here, we demonstrated that abnormal iron and lipid metabolism occurred in patients with intrauterine adhesions (IUA) and murine models. Ferroptosis has been proven to contribute to the progression of fibrotic diseases. Our results revealed that pharmacological activation of ferroptosis by Erastin aggravated endometrial fibrosis, while inhibition of ferroptosis by Ferrostatin-1 ameliorated endometrial fibrosis in vivo. Moreover, ferroptosis of macrophages was significantly upregulated in endometria of IUA murine models. Of note, transcriptome profiles revealed that CD36 gene expression was significantly increased in patients with IUA and immunofluorescence analysis showed CD36 protein was mainly located in macrophages. Silencing CD36 in macrophages could reverse cell ferroptosis. Dual luciferase reporter assay revealed that CD36 was the direct target of activation transcription factor 3 (ATF3). Furthermore, through establishing coculture system and IUA murine models, we found that hUC-MSCs had a protective role against macrophage ferroptosis and alleviated endometrial fibrosis related to decreased CD36 and ATF3. The effect of hUC-MSCs on macrophage ferroptosis was attributed to the upregulation of amphiregulin (AREG). Our data highlighted that macrophage ferroptosis occurred in endometrial fibrosis via the ATF3-CD36 pathway and hUC-MSCs protected against macrophage ferroptosis to alleviate endometrial fibrosis via secreting AREG. These findings provided a potential target for therapeutic implications of endometrial fibrosis.

IL-4-induced M2 macrophages inhibit fibrosis of endometrial stromal cells

BACKGROUND

Intrauterine adhesions (IUA) refers to endometrial fibrosis caused by irreversible damage of the endometrial basal layer. As the key regulators in tissue repair, regeneration, and fibrosis, macrophages play an essential role in endometrial regeneration and repair during the normal menstrual cycle. However, the mechanism of macrophages involved in IUA remains unclear.

METHODS

In the late stages of proliferation, the endometrium was collected to make paraffin sections. HE and Masson staining were used to observing endometrial morphology and endometrial fibrosis. Immunohistochemistry and Western blotting were used to detect the expression level of fibrosis indexes COL1A1 and α-SMA. The macrophage infiltration was evaluated by immunohistochemistry for the expression levels of CD 206 and CD163. Next, we cultured the primary human endometrial stromal cells (HESCs), and then an IUA cell model was established with 10 ng/ml TGF-β1 for 72 h. THP 1 cells were differentiated by 100 ng/ml PMA into macrophages for 48 h, then macrophages were polarized to M2 macrophages by 20 ng/ml IL-4 for 24 h. The culture supernatants (M(IL-4) -S) of M2 macrophages were applied to the IUA cell model. The expression of fibrosis markers was then assessed using immunofluorescence and Western blotting.

RESULTS

The results show that Patients with IUA have fewer endometrial glands and significantly increased fibrosis levels. Moreover, the infiltration of CD206-positive (M2) macrophages was significantly reduced in IUA patients, and negatively correlated with the expression of endometrial fibrosis indexes α-SMA and COL1A1. In addition, the primary HESCs treated with 10 ng/ml TGF-β1 for 72 h were found to have significantly increased levels of fibrosis indexes. Furthermore, supernatants from IL4-induced M2 macrophages inhibit the TGF-β1-induced fibrosis of HESCs.

CONCLUSIONS

M2 macrophages may negatively regulate the expression of COL1A1 and α-SMA, inhibiting the TGF-β1-induced fibrosis of HESCs. Our study suggests that targeting macrophage phenotypes and promoting the polarization of macrophages to M2 may become a novel strategy for the clinical treatment of IUA.

Murine modeling of menstruation identifies immune correlates of protection during Chlamydia muridarum challenge

The menstrual cycle influences the risk of acquiring sexually transmitted infections (STIs), including Chlamydia trachomatis (C. trachomatis), although the underlying immune contributions are poorly defined. A mouse model simulating the immune-mediated process of menstruation could provide valuable insights into tissue-specific determinants of protection against chlamydial infection within the cervicovaginal and uterine mucosae comprising the female reproductive tract (FRT). Here, we used the pseudopregnancy approach in naïve C57Bl/6 mice and performed vaginal challenge with Chlamydia muridarum (C. muridarum) at decidualization, endometrial tissue remodeling, or uterine repair. This strategy identified that the time frame comprising uterine repair correlated with robust infection and greater bacterial burden as compared with mice on hormonal contraception, while challenges during endometrial remodeling were least likely to result in a productive infection. By comparing the infection site at early time points following chlamydial challenge, we found that a greater abundance of innate effector populations and proinflammatory signaling, including IFNγ correlated with protection. FRT immune profiling in uninfected mice over pseudopregnancy or in pig-tailed macaques over the menstrual cycle identified NK cell infiltration into the cervicovaginal tissues and lumen over the course of endometrial remodeling. Notably, NK cell depletion over this time frame reversed protection, with mice now productively infected with C. muridarum following challenge. This study shows that the pseudopregnancy murine menstruation model recapitulates immune changes in the FRT as a result of endometrial remodeling and identifies NK cell localization at the FRT as essential for immune protection against primary C. muridarum infection.

Endometrial TGFβ signaling fosters early pregnancy development by remodeling the fetomaternal interface

The endometrium is a unique and highly regenerative tissue with crucial roles during the reproductive lifespan of a woman. As the first site of contact between mother and embryo, the endometrium, and its critical processes of decidualization and immune cell recruitment, play a leading role in the establishment of pregnancy, embryonic development, and reproductive capacity. These integral processes are achieved by the concerted actions of steroid hormones and a myriad of growth factor signaling pathways. This review focuses on the roles of the transforming growth factor β (TGFβ) pathway in the endometrium during the earliest stages of pregnancy through the lens of immune cell regulation and function. We discuss how key ligands in the TGFβ family signal through downstream SMAD transcription factors and ultimately remodel the endometrium into a state suitable for embryo implantation and development. We also focus on the key roles of the TGFβ signaling pathway in recruiting uterine natural killer cells and their collective remodeling of the decidua and spiral arteries. By providing key details about immune cell populations and TGFβ signaling within the endometrium, it is our goal to shed light on the intricate remodeling that is required to achieve a successful pregnancy.

Infertility in patients with uterine fibroids: a debate about the hypothetical mechanisms

Fibroids are benign tumours of the myometrium and are the most common gynaecologic abnormality. Although most fibroids are asymptomatic, they can cause symptoms like heavy menstrual bleeding, pelvic pain, sexual dysfunction, pressure complaints, and infertility. The association between fibroids and infertility has been debated for decades. It is generally acknowledged that the closer the fibroid is to the uterine cavity and the endometrium lining, the more unfavourable effect it might have on fertility, reducing the odds for successful implantation and gestation. Based on the limited available literature, we propose and discuss seven hypotheses on the underlying mechanism by which fibroids may reduce fertility. (i) Fibroids can cause sexual dysfunction, as fibroids can cause dyspareunia, pelvic pain, and prolonged and heavy menstrual bleeding, which could interfere with sexual arousal and as a consequence the frequency of intercourse, resulting in a reduced probability of conception. (ii) Mechanical compression by fibroids on theinterstitial part of the fallopian tubes or deformation of uterine cavity could disturb oocyte and sperm transport. (iii) Fibroids can disturb peristalsis of the junctional zone in the myometrium, which could negatively influence oocyte and sperm transport as well as implantation. In addition, fibroids could induce a detrimental environment for implantation in other ways, by: (iv) changing the vagino-uterine microbiome; (v) disturbing the levels of inflammation and autophagy; (vi) inducing molecular changes in the endometrium; and (vii) inducing aberrant angiogenesis and altering the endometrial blood supply. After the discussion of these hypotheses, the implication of the influence of fibroids on early pregnancy loss is discussed. Surgical fibroid treatment is not tailored nor focussed on the pathophysiology of the fibroid; consequently it may be accompanied by recurrence of fibroids and risks of complications. Unravelling the pathogenic mechanisms about how fibroids influence fertility is essential to evolve classic surgical fibroid treatment. Instead of treatment of fibroid-related symptoms, the research should supports development of fibroid-targeted (pharmaceutical) treatment that is compatible with an active wish to become pregnant.

Targeting CD301+ macrophages inhibits endometrial fibrosis and improves pregnancy outcome

Macrophages are a key and heterogeneous cell population involved in endometrial repair and regeneration during the menstrual cycle, but their role in the development of intrauterine adhesion (IUA) and sequential endometrial fibrosis remains unclear. Here, we reported that CD301+ macrophages were significantly increased and showed their most active interaction with profibrotic cells in the endometria of IUA patients compared with the normal endometria by single-cell RNA sequencing, bulk RNA sequencing, and experimental verification. Increasing CD301+ macrophages promoted the differentiation of endometrial stromal cells into myofibroblasts and resulted in extracellular matrix accumulation, which destroyed the physiological architecture of endometrial tissue, drove endometrial fibrosis, and ultimately led to female infertility or adverse pregnancy outcomes. Mechanistically, CD301+ macrophages secreted GAS6 to activate the AXL/NF-κB pathway, upregulating the profibrotic protein synthesis. Targeted deletion of CD301+ macrophages or inhibition of AXL by Bemcentinib blunted the pathology and improved the outcomes of pregnancy in mice, supporting the therapeutic potential of targeting CD301+ macrophages for treating endometrial fibrosis.

S100A8 and S100A9 are associated with endometrial shedding during menstruation

Matrix metalloproteinases (MMPs) and their major source, endometrial stromal cells (ESCs), play important roles in menstruation. However, other mechanisms in endometrial shedding may be unexplored. This study focused on four proteins: S100A8 and S100A9 (alarmins) are binding partners and induce MMPs, MMP-3 cycle-dependently plays a key role in the proteolytic cascade, and CD147, which has S100A9 as its ligand, induces MMPs. Immunostaining for these proteins was performed on 118 resected specimens. The percentage and location of each positive reaction in ESCs were measured and compared using Image J. The influence of leukocytes on S100A8 or S100A9 immunopositivity was also examined. From the premenstrual phase, S100A8 and MMP-3 began to have overlapping expressions in ESCs of the superficial layer, and ESC detachment was found within these sites. S100A9 was expressed from the late secretory phase and CD147 already from earlier. Later, the expression sites of S100A9 and CD147 included those of S100A8. Before menstruation, S100A8 or S100A9 expression was not affected by leukocytes. These results suggest that the local formation of S100A8/S100A9 complex, which occurs specifically in ESCs upon progesterone withdrawal, induces the local expression of MMP-3 and serves as a switch to the lysis phase.

Hormonal stimulation reduces numbers and impairs function of human uterine natural killer cells during implantation

STUDY QUESTION

How does an altered maternal hormonal environment, such as that seen during superovulation with gonadotropins in ART, impact human uterine immune cell distribution and function during the window of implantation?

SUMMARY ANSWER

Hormonal stimulation with gonadotropins alters abundance of maternal immune cells including uterine natural killer (uNK) cells and reduces uNK cell ability to promote extravillous trophoblast (EVT) invasion.

WHAT IS KNOWN ALREADY

An altered maternal hormonal environment, seen following ART, can lead to increased risk for adverse perinatal outcomes associated with disordered placentation. Maternal immune cells play an essential role in invasion of EVTs, a process required for proper establishment of the placenta, and adverse perinatal outcomes have been associated with altered immune cell populations. How ART impacts maternal immune cells and whether this can in turn affect implantation and placentation in humans remain unknown.

STUDY DESIGN, SIZE, DURATION

A prospective cohort study was carried out between 2018 and 2021 on 51 subjects: 20 from natural cycles 8 days after LH surge; and 31 from stimulated IVF cycles 7 days after egg retrieval.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Endometrial biopsies and peripheral blood samples were collected during the window of implantation in subjects with regular menstrual cycles or undergoing superovulation. Serum estradiol and progesterone levels were measured by chemiluminescent competitive immunoassay. Immune cell populations in blood and endometrium were analyzed using flow cytometry. uNK cells were purified using fluorescence-activated cell sorting and were subjected to RNA sequencing (RNA-seq). Functional changes in uNK cells due to hormonal stimulation were evaluated using the implantation-on-a-chip (IOC) device, a novel bioengineered platform using human primary cells that mimics early processes that occur during pregnancy in a physiologically relevant manner. Unpaired t-tests, one-way ANOVA, and pairwise multiple comparison tests were used to statistically evaluate differences.

MAIN RESULTS AND THE ROLE OF CHANCE

Baseline characteristics were comparable for both groups. As expected, serum estradiol levels on the day of biopsy were significantly higher in stimulated (superovulated) patients (P = 0.0005). In the setting of superovulation, we found an endometrium-specific reduction in the density of bulk CD56+ uNK cells (P < 0.05), as well as in the uNK3 subpopulation (P = 0.025) specifically (CD103+ NK cells). In stimulated samples, we also found that the proportion of endometrial B cells was increased (P < 0.0001). Our findings were specific to the endometrium and not seen in peripheral blood. On the IOC device, uNK cells from naturally cycling secretory endometrium promote EVT invasion (P = 0.03). However, uNK cells from hormonally stimulated endometrium were unable to significantly promote EVT invasion, as measured by area of invasion, depth of invasion, and number of invaded EVTs by area. Bulk RNA-seq of sorted uNK cells from stimulated and unstimulated endometrium revealed changes in signaling pathways associated with immune cell trafficking/movement and inflammation.

LIMITATIONS, REASONS FOR CAUTION

Patient numbers utilized for the study were low but were enough to identify significant overall population differences in select immune cell types. With additional power and deeper immune phenotyping, we may detect additional differences in immune cell composition of blood and endometrium in the setting of hormonal stimulation. Flow cytometry was performed on targeted immune cell populations that have shown involvement in early pregnancy. A more unbiased approach might identify changes in novel maternal immune cells not investigated in this study. We performed RNA-seq only on uNK cells, which demonstrated differences in gene expression. Ovarian stimulation may also impact gene expression and function of other subsets of immune cells, as well as other cell types within the endometrium. Finally, the IOC device, while a major improvement over existing in vitro methods to study early pregnancy, does not include all possible maternal cells present during early pregnancy, which could impact functional effects seen. Immune cells other than uNK cells may impact invasion of EVTs in vitro and in vivo, though these remain to be tested.

WIDER IMPLICATIONS OF THE FINDINGS

These findings demonstrate that hormonal stimulation affects the distribution of uNK cells during the implantation window and reduces the proinvasive effects of uNK cells during early pregnancy. Our results provide a potential mechanism by which fresh IVF cycles may increase risk of disorders of placentation, previously linked to adverse perinatal outcomes.

STUDY FUNDING/COMPETING INTEREST(S)

Research reported in this publication was supported by the University of Pennsylvania University Research Funding (to M.M.), the Eunice Kennedy Shriver National Institute of Child Health and Human Development (P50HD068157 to M.M., S.S., and S.M.), National Center for Advancing Translational Sciences of the National Institutes of Health (TL1TR001880 to J.K.), the Institute for Translational Medicine and Therapeutics of the Perelman School of Medicine at the University of Pennsylvania, the Children's Hospital of Philadelphia Research Institute (to S.M.G.), and the National Institute of Allergy and Infectious Diseases (K08AI151265 to S.M.G.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. All authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Dysregulation of immune response in PCOS organ system

Polycystic ovary syndrome (PCOS) is the most common reproductive endocrine disorder affecting women, which can lead to infertility. Infertility, obesity, hirsutism, acne, and irregular menstruation are just a few of the issues that PCOS can be linked to. PCOS has a complicated pathophysiology and a range of clinical symptoms. Chronic low-grade inflammation is one of the features of PCOS. The inflammatory environment involves immune and metabolic disturbances. Numerous organ systems across the body, in addition to the female reproductive system, have been affected by the pathogenic role of immunological dysregulation in PCOS in recent years. Insulin resistance and hyperandrogenism are associated with immune cell dysfunction and cytokine imbalance. More importantly, obesity is also involved in immune dysfunction in PCOS, leading to an inflammatory environment in women with PCOS. Hormone, obesity, and metabolic interactions contribute to the pathogenesis of PCOS. Hormone imbalance may also contribute to the development of autoimmune diseases. The aim of this review is to summarize the pathophysiological role of immune dysregulation in various organ systems of PCOS patients and provide new ideas for systemic treatment of PCOS in the future.

Mixed-Culture Propagation of Uterine-Tissue-Resident Macrophages and Their Expression Properties of Steroidogenic Molecules

Tissue-resident macrophages (Mø) play tissue/organ-specific roles, and the physiological/pathological implications of uterine Mø in fertility and infertility are not yet fully understood. Herein, we report a simple propagation method for tissue-resident Mø by mixed culture with the respective tissue/organ-residing cells as the niche. We successfully propagated mouse uterine Mø by mixed culture with fibroblastic cells that exhibited properties of endometrial stromal cells. Propagated mouse uterine Mø were CD206- and arginase-1-positive; iNOS- and MHC-II-negative, indicating M2 polarization; and highly phagocytic, similar to endometrial Mø. Furthermore, uterine Mø were observed to express steroidogenic molecules including SRD5A1 and exhibited gap junction formation, likely with endometrial stromal cells. Accordingly, uterine Mø propagated by mixed culture may provide a new tool for studying immune-endocrine interactions related to fertility and infertility, particularly androgen's intracrine actions in preparing the uterine tissue environment to support implantation and pregnancy as well as in the etiology of endometriosis.

Characterising the immune cell phenotype of ectopic adenomyosis lesions compared with eutopic endometrium: A systematic review

Inflammation is implicated in the symptomatology and the pathogenesis of adenomyosis. Injury at the endo-myometrial interface causes inflammation and may facilitate the invasion of endometrium into the myometrium, forming adenomyosis lesions. Their presence causes local inflammation, resulting in heavy menstrual bleeding, chronic pelvic pain, and subfertility. Immunological differences have been described in the eutopic endometrium from women with adenomyosis compared to healthy endometrium, and differences are also expected in the adenomyotic lesions compared with the correctly sited eutopic endometrium. This systematic review retrieved relevant articles from three databases with additional manual citation chaining from inception to 24th October 2022. Twenty-two eligible studies were selected in accordance with PRISMA guidelines. Risk of bias assessments were performed, and the findings presented thematically. Ectopic endometrial stroma contained an increased density of macrophages compared with eutopic endometrium in adenomyosis. This was associated with an increase in pro-inflammatory cytokines (IL-6, IL-8, ILβ-1, C-X-C Motif Chemokine Receptor 1(CXCR1), Monocyte Chemoattractant Protein-1 (MCP-1)), and an imbalance of anti-inflammatory cytokines (IL-22, IL-37). Cells in ectopic lesions also contained a higher levels of toll-like receptors and immune-mediated enzymes. However, the studies were heterogeneous, with inconsistent reporting of immune cell density within epithelial or stromal compartments, and inclusion of samples from different menstrual cycle phases in the same group for analysis. A detailed understanding of the immune cell phenotypes present in eutopic and ectopic endometrium in adenomyosis and associated dysregulated inflammatory processes will provide further insight into the pathogenesis, to enable identification of fertility-sparing treatments as an alternative to hysterectomy.

Decreased Glycolysis at Menstruation is Associated with Increased Menstrual Blood Loss

Heavy menstrual bleeding (HMB) is common and severely affects the quality of life of the afflicted women. While HMB is known to be caused by impaired endometrial repair after menstruation, its more proximate cause remains unknown. To investigate whether glycolysis plays any role in endometrial repair and thus HMB, we conducted two mouse experiments using a mouse model of simulated menstruation. We performed immunohistochemistry analyses of proteins involved in glycolysis as well as pro- and anti-inflammatory cytokines in endometrium from decidualized and non-decidualized uterine horns. We also assessed the extent of endometrial repair by staging endometrial morphology from decidualization to full repair using histological scoring of uterine sections and quantitated the amount of menstrual blood loss (MBL). In addition, we employed the scratch assay and the CCK-8 assay to evaluate the effect of glycolysis suppression on cellular migration and proliferation, respectively. Finally, we performed an immunohistochemistry analysis of HK2 in endometrium from women with adenomyosis who experienced either moderate/heavy or excessive MBL. We found that endometrial repair coincided with increased glycolysis in endometrium and glycolysis suppression delayed endometrial repair, resulting in increased MBL. Additionally, glycolysis suppression significantly inhibited the proliferative and migratory capability of endometrial cells, and disrupted normal endometrial repair even when hypoxia was maintained. Women with adenomyosis who experienced excessive MBL had significantly lower HK2 staining than those who experienced moderate/heavy MBL. Thus, our study highlights the importance of glycolysis as well as inflammation in optimal endometrial repair, and provides clues for the cause of HMB in women with adenomyosis.

Setting a stage: Inflammation during preeclampsia and postpartum

Preeclampsia (PE) is a leading cause of maternal and fetal mortality worldwide. The immune system plays a critical role in normal pregnancy progression; however, inappropriate inflammatory responses have been consistently linked with PE pathophysiology. This inflammatory phenotype consists of activation of the innate immune system, adaptive immune system, and increased inflammatory mediators in circulation. Moreover, recent studies have shown that the inflammatory profile seen in PE persists into the postpartum period. This manuscript aims to highlight recent advances in research relating to inflammation in PE as well as the inflammation that persists postpartum in women after a PE pregnancy. With the advent of the COVID-19 pandemic, there has been an increase in obstetric disorders associated with COVID-19 infection during pregnancy. This manuscript also aims to shed light on the relationship between COVID-19 infection during pregnancy and the increased incidence of PE in these women.

Immunomodulation for unexplained recurrent implantation failure: where are we now?

In brief

Immune dysfunction may contribute to or cause recurrent implantation failure. This article summarizes normal and pathologic immune responses at implantation and critically appraises currently used immunomodulatory therapies.

Abstract

Recurrent implantation failure (RIF) may be defined as the absence of pregnancy despite the transfer of ≥3 good-quality blastocysts and is unexplained in up to 50% of cases. There are currently no effective treatments for patients with unexplained RIF. Since the maternal immune system is intricately involved in mediating endometrial receptivity and embryo implantation, both insufficient and excessive endometrial inflammatory responses during the window of implantation are proposed to lead to implantation failure. Recent strategies to improve conception rates in RIF patients have focused on modulating maternal immune responses at implantation, through either promoting or suppressing inflammation. Unfortunately, there are no validated, readily available diagnostic tests to confirm immune-mediated RIF. As such, immune therapies are often started empirically without robust evidence as to their efficacy. Like other chronic diseases, patient selection for immunomodulatory therapy is crucial, and personalized medicine for RIF patients is emerging. As the literature on the subject is heterogenous and rapidly evolving, we aim to summarize the potential efficacy, mechanisms of actions and side effects of select therapies for the practicing clinician.

How do pre-pregnancy endometrial macrophages contribute to pregnancy?

Macrophages are professional phagocytes with a wide distribution in all tissues throughout the body. Macrophages play a crucial role in homeostasis and numerous physiological processes beyond innate and adaptive immunity, including cellular debris removal, metabolic regulation, tissue repair, and tissue remodeling. Uterine macrophages are a heterogeneous and highly plastic subset of immune cells regulated by the local microenvironment and, in addition to their anti-inflammatory and anti-infective functions, support the establishment and maintenance of pregnancy. Comprehensive reviews have summarized the role of decidual macrophages during pregnancy. However, the distribution of macrophages in the endometrium prior to pregnancy, their functional remodeling, and the knock-on effects on subsequent pregnancies have not been elucidated. In this review, we focus on 1) how the phenotypes of endometrial macrophages and their interactions with other endometrial cells indicate or contribute to the subsequent pregnancy, 2) the adaptive switching of endometrial macrophages during the initial establishment of pregnancy, 3) and the pregnancy complications and pregnancy-related disorders associated with endometrial macrophages.

Liposome-mediated small RNA delivery to convert the macrophage polarity: A novel therapeutic approach to treat inflammatory uterine disease

Macrophages are present in all tissues for maintaining tissue homeostasis, and macrophage polarization plays a vital role in alleviating inflammation. Therefore, specific delivery of polarization modulators to macrophages in situ is critical for treating inflammatory diseases. We demonstrate that a size-controlled miRNA-encapsulated macrophage-targeting liposomes (miR/MT-Lip) specifically targets macrophages to promote M1-to-M2 polarization conversion, alleviating inflammation without cytotoxicity. miR/MT-Lip, approximately 1.2 μm, showed excellent internalization through phagocytosis and/or macropinocytosis in macrophages. miR-10a/MT-Lip, but not scramble miR-Fluorescein amidite (FAM)/MT-Lip as control, effectively converted the polarization of lipopolysaccharide (LPS)-induced M1 macrophages to M2 in vitro. When miR-10a/MT-Lip was intravenously delivered to mice insulted with LPS for inflammation, the proportion of M2 macrophages was significantly increased without disturbing the population of other immune cells. Furthermore, scramble miR-FAM/MT-Lip was mainly detected in macrophages, but not other immune cells. When our miR/MT-Lip was administered to mice with Asherman's syndrome that suffer from infertility because of sterile uterine inflammation, macrophage-specific targeting of miR-10a/MT-Lip facilitated M1-to-M2 conversion for angiogenesis in the impaired uterus, resulting in restoration of healthy uterine conditions. The results indicate that our MT-Lip encapsulating small RNAs has excellent potential to treat various inflammatory disorders by fine-tuning macrophage polarization in vivo without any side effects.

“Iron triangle” of regulating the uterine microecology: Endometrial microbiota, immunity and endometrium

The uterus is the core place for breeding new life. The balance and imbalance of uterine microecology can directly affect or even dominate the female reproductive health. Emerging data demonstrate that endometrial microbiota, endometrium and immunity play an irreplaceable role in regulating uterine microecology, forming a dynamic iron triangle relationship. Up to nowadays, it remains unclear how the three factors affect and interact with each other, which is also a frontier topic in the emerging field of reproductive tract microecology. From this new perspective, we aim to clarify the relationship and mechanism of the interaction of these three factors, especially their pairwise interactions. Finally, the limitations and future perspectives of the current studies are summarized. In general, these three factors have a dynamic relationship of mutual dependence, promotion and restriction under the physiological or pathological conditions of uterus, among which the regulatory mechanism of microbiota and immunity plays a role of bridge. These findings can provide new insights and measures for the regulation of uterine microecology, the prevention and treatment of endometrial diseases, and the further multi-disciplinary integration between microbiology, immunology and reproductive medicine.

Role of macrophages in the immunopathogenesis of adenomyosis

The aim of the research: to study pathophysiological mechanisms of adenomyosis development by determining the role of macrophages in the uterine microenvironment. Materials and methods: a prospective study has been conducted on 35 women. There were 20 (57.1 %) who had adenomyosis of I degree. The control group consisted of 15 (34.3 %) gynecologically healthy women. The patients underwent general clinical, instrumental (ultrasound, hysteroscopy) examinations. Fragments of the uterine wall obtained by hysterorectoscopy were used for morphological study. The method of immunohistochemical determination of CD68+ and CD163+ macrophages was used to analyze the characteristics of phenotypic equivalents of M1 and M2 macrophages in uterine tissue samples. Results: The increase in the number of macrophages in the myometrium of patients with adenomyosis revealed in this study, which is found in large numbers in the areas of infiltration of the stroma of myometrial cells in close association with the perivascular region, can be regarded as the basis of the mechanism for the formation of endometrioid heterotopia. Furthermore, distortion of the CD68/CD163 ratio of macrophages is characterized by proinflammatory shift. Conclusions: The study's main result is an increase in the quantitative indicators of CD68+ macrophages associated with adenomyosis, which indicates an immunopathological process in adenomyosis.

Artificial intelligence deep learning model assessment of leukocyte counts and proliferation in endometrium from women with and without polycystic ovary syndrome

OBJECTIVE

To study whether artificial intelligence (AI) technology can be used to discern quantitative differences in endometrial immune cells between cycle phases and between samples from women with polycystic ovary syndrome (PCOS) and non-PCOS controls. Only a few studies have analyzed endometrial histology using AI technology, and especially, studies of the PCOS endometrium are lacking, partly because of the technically challenging analysis and unavailability of well-phenotyped samples. Novel AI technologies can overcome this problem.

DESIGN

Case-control study.

SETTING

University hospital-based research laboratory.

PATIENT(S)

Forty-eight women with PCOS and 43 controls. Proliferative phase samples (26 control and 23 PCOS) and luteinizing hormone (LH) surge timed LH+ 7-9 (10 control and 16 PCOS) and LH+ 10-12 (7 control and 9 PCOS) secretory endometrial samples were collected during 2014-2019.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Endometrial samples were stained with antibodies for CD8+ T cells, CD56+ uterine natural killer cells, CD68+ macrophages, and proliferation marker Ki67. Scanned whole slide images were analyzed with an AI deep learning model. Cycle phase differences in leukocyte counts, proliferation rate, and endometrial thickness were measured within the study populations and between the PCOS and control samples. A subanalysis of anovulatory PCOS samples (n = 11) vs. proliferative phase controls (n = 18) was also performed.

RESULT(S)

Automated cell counting with a deep learning model performs well for the human endometrium. The leukocyte numbers and proliferation in the endometrium fluctuate with the menstrual cycle. Differences in leukocyte counts were not observed between the whole PCOS population and controls. However, anovulatory women with PCOS presented with a higher number of CD68+ cells in the epithelium (controls vs. PCOS, median [interquartile range], 0.92 [0.75-1.51] vs. 1.97 [1.12-2.68]) and fewer leukocytes in the stroma (CD8%, 3.72 [2.18-4.20] vs. 1.44 [0.77-3.03]; CD56%, 6.36 [4.43-7.43] vs. 2.07 [0.65-4.99]; CD68%, 4.57 [3.92-5.70] vs. 3.07 [1.73-4.59], respectively) compared with the controls. The endometrial thickness and proliferation rate were comparable between the PCOS and control groups in all cycle phases.

CONCLUSION(S)

Artificial intelligence technology provides a powerful tool for endometrial research because it is objective and can efficiently analyze endometrial compartments separately. Ovulatory endometrium from women with PCOS did not differ remarkably from the controls, which may indicate that gaining ovulatory cycles normalizes the PCOS endometrium and enables normalization of leukocyte environment before implantation. Deviant endometrial leukocyte populations observed in anovulatory women with PCOS could be interrelated with the altered endometrial function observed in these women.

Endometrial macrophages in health and disease

Macrophages are present in the endometrium throughout the menstrual cycle and are most abundant during menstruation. Endometrial macrophages contribute to tissue remodeling during establishment of pregnancy and are thought to play key roles in mediating tissue breakdown and repair during menstruation. Despite these important roles, the phenotype and function of endometrial macrophages remains poorly understood. In this review, we summarize approaches used to characterize endometrial macrophage phenotype, current understanding of the functional role of macrophages in normal endometrial physiology as well as the putative contribution of macrophage dysfunction to women's reproductive health disorders.

Mechanisms of Scarless Repair at Time of Menstruation: Insights From Mouse Models

The human endometrium is a remarkable tissue which may experience up to 400 cycles of hormone-driven proliferation, differentiation and breakdown during a woman's reproductive lifetime. During menstruation, when the luminal portion of tissue breaks down, it resembles a bloody wound with piecemeal shedding, exposure of underlying stroma and a strong inflammatory reaction. In the absence of pathology within a few days the integrity of the tissue is restored without formation of a scar and the endometrium is able to respond appropriately to subsequent endocrine signals in preparation for establishment of pregnancy if fertilization occurs. Understanding mechanisms regulating scarless repair of the endometrium is important both for design of therapies which can treat conditions where this is aberrant (heavy menstrual bleeding, fibroids, endometriosis, Asherman's syndrome) as well as to provide new information that might allow us to reduce fibrosis and scar formation in other tissues. Menstruation only occurs naturally in species that exhibit spontaneous stromal cell decidualization during the fertile cycle such as primates (including women) and the Spiny mouse. To take advantage of genetic models and detailed time course analysis, mouse models of endometrial shedding/repair involving hormonal manipulation, artificial induction of decidualization and hormone withdrawal have been developed and refined. These models are useful in modeling dynamic changes across the time course of repair and have recapitulated key features of endometrial repair in women including local hypoxia and immune cell recruitment. In this review we will consider the evidence that scarless repair of endometrial tissue involves changes in stromal cell function including mesenchyme to epithelial transition, epithelial cell proliferation and multiple populations of immune cells. Processes contributing to endometrial fibrosis (Asherman's syndrome) as well as scarless repair of other tissues including skin and oral mucosa are compared to that of menstrual repair.

Trophoblast-derived interleukin 9 mediates immune cell conversion and contributes to maternal-fetal tolerance

In the maternal-fetal crosstalk, fetal derived trophoblast cells can secret several molecules to regulate immune tolerance such as cytokines and chemokines, besides human leukocyte antigens (HLA) providing. However, the mechanism of these factors in pregnancy is still unknown. Our previous study showed that IL9 could be secreted by trophoblasts and exerted a positive effect on trophoblasts themselves through autocrine signaling. Given the immunoregulatory function of IL9 and its expression in trophoblasts, we hypothesize that IL9 contributes to maternal-fetal tolerance by regulating immune cells, especially CD14+ dendritic cells (DCs) and naïve CD4 + T cells who have essential roles in maternal-fetal immune tolerance. We performed a series of experiments, finding that HTR8/SVneo cells could secrete IL9 in vitro, and this secretion was decreased under hypoxia; both CD14 + DCs and naïve CD4 + T cells expressed IL9 receptors, indicating potential interactions among these cells. In CD14 + DCs, trophoblast-derived IL9 promoted the immature differentiation, and induced the secretion of Th2 cytokines, including IL4 and IL10, shifting the Th1/Th2 ratio to Th2. In naïve CD4 + T cells, IL9 also increased Foxp3 expression and promoted the secretion of Treg cytokines, including TGFβ and IL10, inhibiting pro-inflammatory Th17. Therefore, trophoblasts may act as fetal-derived immune cells to maintain maternal-fetal tolerance by secreting IL9. Given that trophoblast derived IL9 is decreased in preeclampsia, our study provides a new insight into maternal-fetal immunology and immunological disorders in abnormal pregnancy.

Bioinformatics Analysis Identifies Molecular Markers Regulating Development and Progression of Endometriosis and Potential Therapeutic Drugs

Endometriosis, a common disease that presents as polymorphism, invasiveness, and extensiveness, with clinical manifestations including dysmenorrhea, infertility, and menstrual abnormalities, seriously affects quality of life in women. To date, its underlying etiological mechanism of action and the associated regulatory genes remain unclear. This study aimed to identify molecular markers and elucidate mechanisms underlying the development and progression of endometriosis. Specifically, we downloaded five microarray expression datasets, namely, GSE11691, GSE23339, GSE25628, GSE7305, and GSE105764, from the Gene Expression Omnibus (GEO) database. These datasets, obtained from endometriosis tissues, alongside normal controls, were subjected to in-depth bioinformatics analysis for identification of differentially expressed genes (DEGs), followed by analysis of their function and pathways via gene ontology (GO) and KEGG pathway enrichment analyses. Moreover, we constructed a protein–protein interaction (PPI) network to explore the hub genes and modules, and then applied machine learning algorithms support vector machine-recursive feature elimination and least absolute shrinkage and selection operator (LASSO) analysis to identify key genes. Furthermore, we adopted the CIBERSORTx algorithm to estimate levels of immune cell infiltration while the connective map (CMAP) database was used to identify potential therapeutic drugs in endometriosis. As a result, a total of 423 DEGs, namely, 233 and 190 upregulated and downregulated, were identified. On the other hand, a total of 1,733 PPIs were obtained from the PPI network. The DEGs were mainly enriched in immune-related mechanisms. Furthermore, machine learning and LASSO algorithms identified three key genes, namely, apelin receptor (APLNR), C–C motif chemokine ligand 21 (CCL21), and Fc fragment of IgG receptor IIa (FCGR2A). Furthermore, 16 small molecular compounds associated with endometriosis treatment were identified, and their mechanism of action was also revealed. Taken together, the findings of this study provide new insights into the molecular factors regulating occurrence and progression of endometriosis and its underlying mechanism of action. The identified therapeutic drugs and molecular markers may have clinical significance in early diagnosis of endometriosis.

Interleukin-34 accelerates intrauterine adhesions progress related to CX3CR1+ monocytes/macrophages

Intrauterine adhesions (IUA) are characterized by endometrial fibrosis and impose a great challenge for female reproduction. IL-34 is profoundly involved in various fibrotic diseases through regulating the survival, proliferation, and differentiation of monocytes/macrophages. However, it remains unclear how IL-34 regulates monocytes/macrophages in context of IUA. Here, we showed that the expression level of IL-34 and the amount of CX3CR1+ monocytes/macrophages were significantly increased in endometrial tissues of IUA patients. IL-34 promoted the differentiation of monocytes/macrophages, which express CX3CR1 via CSF-1R/P13K/Akt pathway in vitro. Moreover, IL-34-induced CX3CR1+ monocytes/macrophages promoted the differentiation of endometrial stromal cells into myofibroblasts. Of note, IL-34 caused endometrial fibrosis and increased the amount of CX3CR1+ monocytes/macrophages in endometrial tissues in vivo. IL-34 modulated endometrial fibrosis by regulating monocytes/macrophages since the elimination of endometrial monocytes/macrophages significantly suppressed the profibrotic function of IL-34. Finally, blocking of IL-34 in the LPS-IUA model resulted in the improvement of endometrial fibrosis and decreased number of CX3CR1+ monocytes/macrophages. Our studies uncover the novel mechanism of interaction between IL-34-induced CX3CR1+ monocytes/macrophages and endometrial stromal cells in endometrial fibrosis pathogenesis, and highlight IL-34 as a critical target for treating IUA.

Understanding the Impact of Uterine Fibroids on Human Endometrium Function

Uterine fibroids (leiomyomas) are the most common benign gynecological tumors in women of reproductive age worldwide. They cause heavy menstrual bleeding, usually leading to severe anemia, pelvic pain/pressure, infertility, and other debilitating morbidities. Fibroids are believed to be monoclonal tumors arising from the myometrium, and recent studies have demonstrated that fibroids actively influence the endometrium globally. Studies suggest a direct relationship between the number of fibroids removed and fertility problems. In this review, our objective was to provide a complete overview of the origin of uterine fibroids and the molecular pathways and processes implicated in their development and growth, which can directly affect the function of a healthy endometrium. One of the most common characteristics of fibroids is the excessive production of extracellular matrix (ECM) components, which contributes to the stiffness and expansion of fibroids. ECM may serve as a reservoir of profibrotic growth factors such as the transforming growth factor β (TGF-β) and a modulator of their availability and actions. Fibroids also elicit mechanotransduction changes that result in decreased uterine wall contractility and increased myometrium rigidity, which affect normal biological uterine functions such as menstrual bleeding, receptivity, and implantation. Changes in the microRNA (miRNA) expression in fibroids and myometrial cells appear to modulate the TGF-β pathways and the expression of regulators of ECM production. Taken together, these findings demonstrate an interaction among the ECM components, TGF-β family signaling, miRNAs, and the endometrial vascular system. Targeting these components will be fundamental to developing novel pharmacotherapies that not only treat uterine fibroids but also restore normal endometrial function.

Endometriosis and Cancer: Exploring the Role of Macrophages

Endometriosis and cancer have much in common, notably their burgeoning of cells in hypoxic milieus, their invasiveness, and their capacity to trigger remodeling, vascularization, and innervation of other tissues. An important role in these processes is played by permissive microenvironments inhabited by a variety of stromal and immune cells, including macrophages. Remarkable phenotypical plasticity of macrophages makes them a promising therapeutic target; some key issues are the range of macrophage phenotypes characteristic of a particular pathology and the possible manners of its modulation. In both endometriosis and cancer, macrophages guard the lesions from immune surveillance while promoting pathological cell growth, invasion, and metastasis. This review article focuses on a comparative analysis of macrophage behaviors in endometriosis and cancer. We also highlight recent reports on the experimental modulation of macrophage phenotypes in preclinical models of endometriosis and cancer.

Heat Shock Proteins and Their Role in Pregnancy: Redefining the Function of "Old Rum in a New Bottle"

Pregnancy in humans is a multi-step complex physiological process comprising three discrete events, decidualization, implantation and placentation. Its overall success depends on the incremental advantage that each of the preceding stages passes on to the next. The success of these synchronized sequels of events is an outcome of timely coordination between them. The pregnancy events are coordinated and governed primarily by the ovarian steroid hormones, estrogen and progesterone, which are essentially ligand-activated transcription factors. It's well known that intercellular signaling of steroid hormones engages a plethora of adapter proteins that participate in executing the biological functions. This involves binding of the hormone receptor complex to the DNA response elements in a sequence specific manner. Working with Drosophila melanogaster, the heat shock proteins (HSPs) were originally described by Ferruccio Ritossa back in the early 1960s. Over the years, there has been considerable advancement of our understanding of these conserved families of proteins, particularly in pregnancy. Accumulating evidence suggests that endometrial and uterine cells have an abundance of HSP27, HSP60, HSP70 and HSP90, implying their possible involvement during the pregnancy process. HSPs have been found to be associated with decidualization, implantation and placentation, with their dysregulation associated with implantation failure, pregnancy loss and other feto-maternal complications. Furthermore, HSP is also associated with stress response, specifically in modulating the ER stress, a critical determinant for reproductive success. Recent advances suggest a therapeutic role of HSPs proteins in improving the pregnancy outcome. In this review, we summarized our latest understanding of the role of different members of the HSP families during pregnancy and associated complications based on experimental and clinical evidences, thereby redefining and exploring their novel function with new perspective, beyond their prototype role as molecular chaperones.

Endometrial inflammasome activation accompanies menstruation and may have implications for systemic inflammatory events of the menstrual cycle

STUDY QUESTION

Does NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome activation within decidualized endometrial stromal cells accompany menstruation and is this reflected systemically?

SUMMARY ANSWER

Components of the NLRP3 inflammasome immunolocalize to decidualized endometrial stromal cells immediately prior to menstruation, and are activated in an in vitro model of menstruation, as evidenced by downstream interleukin (IL)-1beta and IL-18 release, this being reflected systemically in vivo.

WHAT IS KNOWN ALREADY

Menstruation is a highly inflammatory event associated with activation of NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells), local release of chemokines and cytokines and inflammatory leukocyte influx. Systemically, chemokines and cytokines fluctuate across the menstrual cycle.

STUDY DESIGN, SIZE, DURATION

This study examined the NLRP3 inflammasome and activation of downstream IL-1beta and IL-18 in endometrial tissues from women of known fertility (≥1 previous parous pregnancy) across the menstrual cycle (n ≥ 8 per cycle phase), serum from women during the proliferative, secretory and menstrual phases (≥9 per cycle phase) of the cycle and menstrual fluid collected on Day 2 of menses (n = 18). Endometrial stromal cells isolated from endometrial tissue biopsies (n = 10 in total) were used for an in vitro model of pre-menstrual hormone withdrawal.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Expression and localization of components of the NLRP3 inflammasome (NLRP3 & apoptosis-associated speck-caspase recruit domain [ASC]) in endometrial tissues was performed by immunohistochemistry. Unbiased digital quantification of immunohistochemical staining allowed determination of different patterns of expression across the menstrual cycle. Serum from women across the menstrual cycle was examined for IL-1beta and IL-18 concentrations by ELISA. An in vitro model of hormone withdrawal from estrogen/progestin decidualized endometrial stromal cells was used to more carefully examine activation of the NLRP3 inflammasome. Endometrial stromal cells isolated from endometrial tissue biopsies (n = 10) were treated with estrogen/medroxyprogesterone acetate for 12 days to induce decidualization (assessed by release of prolactin) followed by withdrawal of steroid hormone support. Activation of NLRP3, & ASC in these cells was examined on Days 0-3 after hormone withdrawal by Western immunoblotting. Release of IL-1beta and IL-18 examined during decidualization and across the same time course of hormone withdrawal by ELISA. Specific involvement of NLRP3 inflammasome activation in IL-1beta and IL-18 release after hormone withdrawal was investigated via application of the NLRP3 inflammasome inhibitor MCC950 at the time of hormone withdrawal.

MAIN RESULTS AND THE ROLE OF CHANCE

Critical components of the NLRP3 inflammasome (NLRP3, ASC) were increased in menstrual phase endometrial tissues versus early secretory phase tissues (P < 0.05, n/s, respectively). NLRP3 and ASC were also elevated in the proliferative versus secretory phase of the cycle (P < 0.01, n/s, respectively) with ASC also significantly increased in the late-secretory versus early-secretory phase (P < 0.05). The pattern of activation was reflected in systemic levels of the inflammasome mediators, with IL-1beta and IL-18 elevated in peripheral blood serum during menstruation (Day 2 of menses) versus secretory phase (P = 0.026, P = 0.0042, respectively) and significantly elevated in menstrual fluid (Day 2 of menses) versus systemic levels across all cycle phases, suggesting that local inflammasome activation within the endometrium during menses is reflected by systemic inflammation. NLRP3 and ASC localized to decidualized cells adjacent to the spiral arterioles in the late secretory phase of the menstrual cycle, where the menstrual cascade is thought to be initiated, and to endometrial leukocytes during the menstrual phase. NLRP3 also localized to glandular epithelial cells during the late-secretory/menstrual phases. Localization of both NLRP3 and ASC switched from predominant epithelial localization during the early-secretory phase to stromal localization during the late-secretory/menstrual phase. Using an in vitro model of hormone withdrawal from decidualized human endometrial stromal cells, we demonstrated progressive activation of NLRP3 and ASC after hormone withdrawal increasing from Day 0 of withdrawal/Day 12 of decidualization to Day 3 of withdrawal. Downstream release of IL-1beta and IL-18 from decidualized stromal cells after hormone withdrawal followed the same pattern with the role of NLRP3 inflammasome activation confirmed via the inhibition of IL-1beta and IL-18 release upon application of MCC950.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This study uses descriptive and semi-quantitative measures of NLRP3 inflammasome activation within endometrial tissues. Further, the in vitro model of pre-menstrual hormone withdrawal may not accurately recapitulate the in vivo environment as only one cell type is present and medroxyprogesterone acetate replaced natural progesterone due to its longer stability.

WIDER IMPLICATIONS OF THE FINDINGS

We provide novel evidence that the NLRP3 inflammasome is activated within decidualized endometrial stromal cells immediately prior to menses and that local activation of the inflammasome within the endometrium appears to be reflected systemically in by activation of downstream IL-1beta and IL-18. Given the prevalence of menstrual disorders associated with inflammation including dysmenorrhoea and aspects of pre-menstrual syndrome, the inflammasome could be a novel target for ameliorating such burdens.

STUDY FUNDING/COMPETING INTEREST(S)

The authors have no competing interests. J.E. was supported by a Fielding Foundation fellowship, NHMRC project grants (#1139489 and #1141946) and The Hudson Institute of Medical Research. L.A.S. was supported by The Hudson Institute of Medical Research and J.H. by an Australian Government Research Training Program Scholarship. We acknowledge the Victorian Government's Operating Infrastructure funding to the Hudson Institute.

TRIAL REGISTRATION NUMBER

N/A.

Identification of genes associated with endometrial cell ageing

Ageing of the uterine endometrium is a critical factor that affects reproductive success, but the mechanisms associated with uterine ageing are unclear. In this study, we conducted a qualitative examination of age-related changes in endometrial tissues and identified candidate genes as markers for uterine ageing. Gene expression patterns were assessed by two RNA-sequencing experiments using uterine tissues from wild type (WT) C57BL/6 mice. Gene expression data obtained by RNA-sequencing were validated by real-time PCR. Genes expressing the pro-inflammatory cytokines Il17rb and chemokines Cxcl12 and Cxcl14 showed differential expression between aged WT mice and a group of mice composed of 5- and 8-week-old WT (young) animals. Protein expression levels of the above-mentioned genes and of IL8, which functions downstream of IL17RB, were analysed by quantitative immunohistochemistry of unaffected human endometrium tissue samples from patients in their 20s and 40s (10 cases each). In the secretory phase samples, 3,3'- diaminobenzidine staining intensities of IL17RB, CXCL12 and CXCL14 for patients in their 40s were significantly higher than that for patients in their 20s, as detected by a Mann-hitney U test. These results suggest that these genes are candidate markers for endometrial ageing and for prediction of age-related infertility, although confirmation of these findings is needed in larger studies involving fertile and infertile women.

Ovarian hormones-autophagy-immunity axis in menstruation and endometriosis

Menstruation occurs in few species and involves a cyclic process of proliferation, breakdown and regeneration under the control of ovarian hormones. Knowledge of normal endometrial physiology, as it pertains to the regulation of menstruation, is essential to understand disorders of menstruation. Accumulating evidence indicates that autophagy in the endometrium, under the regulation of ovarian hormones, can result in the infiltration of immune cells, which plays an indispensable role in the endometrium shedding, tissue repair and prevention of infections during menstruation. In addition, abnormal autophagy levels, together with resulting dysregulated immune system function, are associated with the pathogenesis and progression of endometriosis. Considering its potential value of autophagy as a target for the treatment of menstrual-related and endometrium-related disorders, we review the activity and function of autophagy during menstrual cycles. The role of the estrogen/progesterone-autophagy-immunity axis in endometriosis are also discussed.

Single-cell profiling of the human decidual immune microenvironment in patients with recurrent pregnancy loss

Maintaining homeostasis of the decidual immune microenvironment at the maternal–fetal interface is essential for placentation and reproductive success. Although distinct decidual immune cell subpopulations have been identified under normal conditions, systematic understanding of the spectrum and heterogeneity of leukocytes under recurrent miscarriage in human deciduas remains unclear. To address this, we profiled the respective transcriptomes of 18,646 primary human decidual immune cells isolated from patients with recurrent pregnancy loss (RPL) and healthy controls at single-cell resolution. We discovered dramatic differential distributions of immune cell subsets in RPL patients compared with the normal decidual immune microenvironment. Furthermore, we found a subset of decidual natural killer (NK) cells that support embryo growth were diminished in proportion due to abnormal NK cell development in RPL patients. We also elucidated the altered cellular interactions between the decidual immune cell subsets in the microenvironment and those of the immune cells with stromal cells and extravillous trophoblast under disease state. These results provided deeper insights into the RPL decidual immune microenvironment disorder that are potentially applicable to improve the diagnosis and therapeutics of this disease.

Physiomimetic Models of Adenomyosis

Adenomyosis remains an enigmatic disease in the clinical and research communities. The high prevalence, diversity of morphological and symptomatic presentations, array of potential etiological explanations, and variable response to existing interventions suggest that different subgroups of patients with distinguishable mechanistic drivers of disease may exist. These factors, combined with the weak links to genetic predisposition, make the entire spectrum of the human condition challenging to model in animals. Here, after an overview of current approaches, a vision for applying physiomimetic modeling to adenomyosis is presented. Physiomimetics combines a system's biology analysis of patient populations to generate hypotheses about mechanistic bases for stratification with in vitro patient avatars to test these hypotheses. A substantial foundation for three-dimensional (3D) tissue engineering of adenomyosis lesions exists in several disparate areas: epithelial organoid technology; synthetic biomaterials matrices for epithelial–stromal coculture; smooth muscle 3D tissue engineering; and microvascular tissue engineering. These approaches can potentially be combined with microfluidic platform technologies to model the lesion microenvironment and can potentially be coupled to other microorgan systems to examine systemic effects. In vitro patient-derived models are constructed to answer specific questions leading to target identification and validation in a manner that informs preclinical research and ultimately clinical trial design.

Uterine decidual niche modulates the progressive dedifferentiation of spiral artery vascular smooth muscle cells during human pregnancy†

Uterine spiral artery (SPA) remodeling is a crucial event during pregnancy to provide enough blood supply to maternal-fetal interface and meet the demands of the growing fetus. Along this process, the dynamic change and the fate of spiral artery vascular smooth muscle cells (SPA-VSMCs) have long been debatable. In the present study, we analyzed the cell features of SPA-VSMCs at different stages of vascular remodeling in human early pregnancy, and we demonstrated the progressively morphological change of SPA-VSMCs at un-remodeled (Un-Rem), remodeling, and fully remodeled (Fully-Rem) stages, indicating the extravillous trophoblast (EVT)-independent and EVT-dependent phases of SPA-VSMC dedifferentiation. In vitro experiments in VSMC cell line revealed the efficient roles of decidual stromal cells, decidual natural killer cells (dNK), decidual macrophages, and EVTs in inducing VSMCs dedifferentiation. Importantly, the potential transformation of VSMC toward CD56+ dNKs was displayed by immunofluorescence-DNA in-situ hybridization-proximity ligation and chromatin immunoprecipitation assays for H3K4dime modification in the myosin heavy chain 11 (MYH11) promoter region. The findings clearly illustrate a cascade regulation of the progressive dedifferentiation of SPA-VSMCs by multiple cell types in uterine decidual niche and provide new evidences to reveal the destination of SPA-VSMCs during vascular remodeling.

Menstruation: science and society

Women's health concerns are generally underrepresented in basic and translational research, but reproductive health in particular has been hampered by a lack of understanding of basic uterine and menstrual physiology. Menstrual health is an integral part of overall health because between menarche and menopause, most women menstruate. Yet for tens of millions of women around the world, menstruation regularly and often catastrophically disrupts their physical, mental, and social well-being. Enhancing our understanding of the underlying phenomena involved in menstruation, abnormal uterine bleeding, and other menstruation-related disorders will move us closer to the goal of personalized care. Furthermore, a deeper mechanistic understanding of menstruation-a fast, scarless healing process in healthy individuals-will likely yield insights into a myriad of other diseases involving regulation of vascular function locally and systemically. We also recognize that many women now delay pregnancy and that there is an increasing desire for fertility and uterine preservation. In September 2018, the Gynecologic Health and Disease Branch of the Eunice Kennedy Shriver National Institute of Child Health and Human Development convened a 2-day meeting, "Menstruation: Science and Society" with an aim to "identify gaps and opportunities in menstruation science and to raise awareness of the need for more research in this field." Experts in fields ranging from the evolutionary role of menstruation to basic endometrial biology (including omic analysis of the endometrium, stem cells and tissue engineering of the endometrium, endometrial microbiome, and abnormal uterine bleeding and fibroids) and translational medicine (imaging and sampling modalities, patient-focused analysis of menstrual disorders including abnormal uterine bleeding, smart technologies or applications and mobile health platforms) to societal challenges in health literacy and dissemination frameworks across different economic and cultural landscapes shared current state-of-the-art and future vision, incorporating the patient voice at the launch of the meeting. Here, we provide an enhanced meeting report with extensive up-to-date (as of submission) context, capturing the spectrum from how the basic processes of menstruation commence in response to progesterone withdrawal, through the role of tissue-resident and circulating stem and progenitor cells in monthly regeneration-and current gaps in knowledge on how dysregulation leads to abnormal uterine bleeding and other menstruation-related disorders such as adenomyosis, endometriosis, and fibroids-to the clinical challenges in diagnostics, treatment, and patient and societal education. We conclude with an overview of how the global agenda concerning menstruation, and specifically menstrual health and hygiene, are gaining momentum, ranging from increasing investment in addressing menstruation-related barriers facing girls in schools in low- to middle-income countries to the more recent "menstrual equity" and "period poverty" movements spreading across high-income countries.

Origin and Pathogenic Mechanisms of Uterine Adenomyosis: What Is Known So Far

Uterine adenomyosis is a benign disease, commonly encountered in reproductive-age women and responsible for chronic pelvic pain, abnormal uterine bleeding, and infertility. Although the exact origin and pathogenic mechanisms involved in adenomyosis still need to be elucidated, significant progress has been made over recent years. Ever since the theory of endometrium invaginating the myometrium via a traumatized interface was first proposed, numerous molecular mechanisms have been reported to participate in this process. At the same time, an alternative theory has suggested de novo development of adenomyotic lesions from metaplasia of Müllerian remnants or adult stem cells. Hence, our understanding of the pathogenesis of adenomyosis has been greatly enhanced and is anticipated to pave the way for development of an effective and safe treatment. The goal of this review is to analyze current knowledge on the origin and pathogenic mechanisms of adenomyosis, ranging from the most widely accepted theories to newly reported data.

A scaffold laden with mesenchymal stem cell-derived exosomes for promoting endometrium regeneration and fertility restoration through macrophage immunomodulation

Endometrial traumas may cause intrauterine adhesions (IUAs), leading to infertility. Conventional methods in clinic have not solved the problem of endometrial regeneration in severe cases. Umbilical cord-derived mesenchymal stem cell (UC-MSC)-based therapies have shown some promising achievements in the treatment of IUAs. However, the limitations of potential tumorigenicity, low infusion and low retention are still controversial and restricted the clinical application of MSCs. In contrast, UC-MSC-derived exosomes exhibit a similar function to their source cells and are expected to overcome these limitations. Therefore, a novel and viable cell-free therapeutic strategy by UC-MSC-derived exosomes was proposed in this study. Here, we designed a construct of exosomes and collagen scaffold (CS/Exos) for endometrial regeneration in a rat endometrium-damage model, and investigated the regeneration mechanism through macrophage immunomodulation. The CS/Exos transplantation potently induced (i) endometrium regeneration, (ii) collagen remodeling, (iii) increased the expression of the estrogen receptor α/progesterone receptor, and (iv) restored fertility. Mechanistically, CS/Exos facilitated CD163⁺ M2 macrophage polarization, reduced inflammation, and increased anti-inflammatory responses in vivo and in vitro. By RNA-seq, miRNAs enriched in exosomes were the main mediator for exosomes-induced macrophage polarization. Overall, we demonstrated that CS/Exos treatment facilitated endometrium regeneration and fertility restoration by immunomodulatory functions of miRNAs. Our research highlights the therapeutic prospects of CS/Exos for the management of IUAs. STATEMENT OF SIGNIFICANCE: Severe endometrial traumas always result in intrauterine adhesions (IUAs) and infertility. The limited outcomes by conventional methods in the clinic make it very important to develop new strategies for endometrium regeneration and fertility restoration. In this study, an exosome-laden scaffold (CS/Exos) was designed and the transplantation of CS/Exos potently induced (i) endometrium regeneration, (ii) collagen remodeling, (iii) increased the expression of the estrogen receptor α/progesterone receptor, and (iv) restored fertility. In mechanism, the construct of CS/Exos facilitated M2 macrophage polarization, reduced inflammation, and increased anti-inflammatory responses. Furthermore, miRNAs enriched in exosomes were the main mediator for exosome-induced macrophage polarization. This study highlights the therapeutic prospects of CS/Exos and the translational application for the management of severe IUAs.

Physiology of the Endometrium and Regulation of Menstruation

The physiological functions of the uterine endometrium (uterine lining) are preparation for implantation, maintenance of pregnancy if implantation occurs, and menstruation in the absence of pregnancy. The endometrium thus plays a pivotal role in reproduction and continuation of our species. Menstruation is a steroid-regulated event, and there are alternatives for a progesterone-primed endometrium, i.e., pregnancy or menstruation. Progesterone withdrawal is the trigger for menstruation. The menstruating endometrium is a physiological example of an injured or “wounded” surface that is required to rapidly repair each month. The physiological events of menstruation and endometrial repair provide an accessible in vivo human model of inflammation and tissue repair. Progress in our understanding of endometrial pathophysiology has been facilitated by modern cellular and molecular discovery tools, along with animal models of simulated menses. Abnormal uterine bleeding (AUB), including heavy menstrual bleeding (HMB), imposes a massive burden on society, affecting one in four women of reproductive age. Understanding structural and nonstructural causes underpinning AUB is essential to optimize and provide precision in patient management. This is facilitated by careful classification of causes of bleeding. We highlight the crucial need for understanding mechanisms underpinning menstruation and its aberrations. The endometrium is a prime target tissue for selective progesterone receptor modulators (SPRMs). This class of compounds has therapeutic potential for the clinical unmet need of HMB. SPRMs reduce menstrual bleeding by mechanisms still largely unknown. Human menstruation remains a taboo topic, and many questions concerning endometrial physiology that pertain to menstrual bleeding are yet to be answered.

The Role of Macrophages in Oocyte Donation Pregnancy: A Systematic Review

The embryo of an oocyte donation (OD) pregnancy is completely allogeneic to the mother, which leads to a more serious challenge for the maternal immune system to tolerize the fetus. It is thought that macrophages are essential in maintaining a healthy pregnancy, by acting in immunomodulation and spiral arterial remodeling. OD pregnancies represent an interesting model to study complex immunologic interactions between the fetus and the pregnant woman since the embryo is totally allogeneic compared to the mother. Here, we describe a narrative review on the role of macrophages and pregnancy and a systematic review was performed on the role of macrophages in OD pregnancies. Searches were made in different databases and the titles and abstracts were evaluated by three independent authors. In total, four articles were included on OD pregnancies and macrophages. Among these articles, some findings are conflicting between studies, indicating that more research is needed in this area. From current research, we could identify that there are multiple subtypes of macrophages, having diverse biological effects, and that the ratio between subtypes is altered during gestation and in aberrant pregnancy. The study of macrophages’ phenotypes and their functions in OD pregnancies might be beneficial to better understand the maternal-fetal tolerance system.

Transcriptome meta-analysis reveals differences of immune profile between eutopic endometrium from stage I-II and III-IV endometriosis independently of hormonal milieu

Eutopic endometrium appears to be crucial for endometriosis development. Despite of the evident importance, data regarding the cellular microenvironment remain unclear. Our objective was to explore the tissue microenvironment heterogeneity, transcripts, and pathways that are enriched in all phases of the menstrual cycle by analysing publicly deposited data derived from whole transcriptome microarrays of eutopic endometria of women with and without endometriosis. A meta-analysis of the transcriptome microarrays was performed using raw data available from a public database. Eligibility criteria included eutopic endometrium samples from women with endometriosis and healthy controls without any pathological condition reported the presence of an adequately reported normal menstrual phase, and samples containing both glandular and stromal components. Raw data were processed using a robust multiarray average method to provide background correction, normalisation, and summarisation. The batch effect was estimated by principal variant component analysis and removed using an empirical Bayes method. Cellular tissue heterogeneity was inferred using the xCell package. Differentially expressed genes were identified based on a 5% adjusted p value and a 2.0-fold change. Pathways were identified by functional enrichment based on the Molecular Signatures Database, a p value of < 5%, and an FDR q value of ≤ 25%. Genes that were more frequently found in pathways were identified using leading edge analysis. In a manner independent of cycle phase, the subpopulations of activated dendritic cells, CD4 T effector memory phenotype cells, eosinophils, macrophages M1, and natural killer T cells (NKT) were all higher in stage I-II endometriosis compared to those in healthy controls. The subpopulations of M2 macrophages and natural killer T cells were elevated in eutopic endometriums from women with stage III-IV endometriosis, and smooth muscle cells were always more prevalent in healthy eutopic endometriums. Among the differently expressed genes, FOS, FOSB, JUNB, and EGR1 were the most frequently mapped within the interaction networks, and this was independent of stage and cycle phase. The enriched pathways were directly related to immune surveillance, stem cell self-renewal, and epithelial mesenchymal transition. PI3K AKT mTOR, TGF signalling, and interferon alpha/gamma responses were enriched exclusively in stage III-IV endometriosis. The cellular microenvironments and immune cell profiles were different between eutopic endometriums from women with stage I-II and stage III-IV endometriosis, and these differences were independent of the hormonal milieu. Specifically, a pro-inflammatory profile was predominant in stage I-II endometriosis, and M1-M2 polarization into eutopic endometrium may be crucial for the progression of the disease. The higher prevalence of NKT cells in eutopic endometriums from women with endometriosis that was independent of cycle phase or staging suggested a sustained stress and/or damage to these eutopic endometriums. Based on this, the results of this meta-analysis are important for identifying challenges and opportunities for future research.

Regulation of mononuclear phagocyte function by the microbiota at mucosal sites

Mucosal tissues contain distinct microbial communities that differ drastically depending on the barrier site, and as such, mucosal immune responses have evolved to be tailored specifically for their location. Whether protective or regulatory immune responses against invading pathogens or the commensal microbiota occur is controlled by local mononuclear phagocytes (MNPs). Comprising macrophages and dendritic cells (DCs), the functions of these cells are highly dependent on the local environment. For example, the intestine contains the greatest bacterial load of any site in the body, and hence, intestinal MNPs are hyporesponsive to bacterial stimulation. This is thought to be one of the major mechanisms by which harmful immune responses directed against the trillions of harmless bacteria that line the gut lumen are avoided. Regulation of MNP function by the microbiota has been characterized in the most depth in the intestine but there are several mucosal sites that also contain their own microbiota. In this review, we present an overview of how MNP function is regulated by the microbiota at mucosal sites, highlighting recent novel pathways by which this occurs in the intestine, and new studies elucidating these interactions at mucosal sites that have been characterized in less depth, including the urogenital tract.

CSF1-associated decrease in endometrial macrophages may contribute to Asherman's syndrome

PROBLEM

Asherman's syndrome (AS) is characterized by endometrial fibrosis leading to intrauterine adhesions and symptoms like hypomenorrhea, infertility, and recurrent pregnancy loss. Macrophages are key regulators of inflammation, tissue repair, regeneration, and fibrosis. However, the role of macrophages in AS remains unclear.

METHOD OF STUDY

Endometrial biopsies of AS patients and controls were collected during the late proliferating phase of menstrual cycle. Fibrosis and proliferation markers were detected by Masson's trichrome staining and immunohistochemistry. Macrophages were examined by immunostaining and flow cytometry. The expression levels of CCL2, CSF1, CSF1R, and GM-CSF were detected by quantitative real-time polymerase chain reaction (q-PCR) and immunohistochemistry. A well-differentiated endometrial cell line Ishikawa (IK) was used for in vitro studies. Macrophages differentiating from THP-1 monocytic cells were polarized by IL-4/IL-13. Their culture supernatants (M(IL-4/13)-S) were applied to H₂ O₂ or bleomycin-damaged IK cells.

RESULTS

In AS patients, endometrial stroma was replaced by fibrous tissue and cell proliferation was reduced. Macrophages in endometrial tissue were mainly alternative activated macrophages and their number was significantly decreased in AS patients. The CSF1 expression level was reduced in AS patients. M(IL-4/13)-S promoted the growth and migration of IK cells and inhibited H₂ O₂ -induced apoptosis. M(IL-4/13)-S protected IK cells from bleomycin-induced fibrosis.

CONCLUSION

Macrophages are critical cells involved in the process of endometrial repair and fibrosis. The decreased amount of endometrial macrophages may be attributed to the reduced expression level of CSF1. Manipulation of macrophage activation/function may provide a novel therapeutic target for AS.

Dynamic Function and Composition Changes of Immune Cells During Normal and Pathological Pregnancy at the Maternal-Fetal Interface

A successful pregnancy requires a fine-tuned and highly regulated balance between immune activation and embryonic antigen tolerance. Since the fetus is semi-allogeneic, the maternal immune system should exert tolerant to the fetus while maintaining the defense against infection. The maternal-fetal interface consists of different immune cells, such as decidual natural killer (dNK) cells, macrophages, T cells, dendritic cells, B cells, and NKT cells. The interaction between immune cells, decidual stromal cells, and trophoblasts constitute a vast network of cellular connections. A cellular immunological imbalance may lead to adverse pregnancy outcomes, such as recurrent spontaneous abortion, pre-eclampsia, pre-term birth, intrauterine growth restriction, and infection. Dynamic changes in immune cells at the maternal-fetal interface have not been clearly stated. While many studies have described changes in the proportions of immune cells in the normal maternal-fetus interface during early pregnancy, few studies have assessed the immune cell changes in mid and late pregnancy. Research on pathological pregnancy has provided clues about these dynamic changes, but a deeper understanding of these changes is necessary. This review summarizes information from previous studies, which may lay the foundation for the diagnosis of pathological pregnancy and put forward new ideas for future studies.

Uterine Immunity and Microbiota: A Shifting Paradigm

The female reproductive tract harbors distinct microbial communities, as in the vagina, cervical canal, uterus, and fallopian tubes. The nature of the vaginal microbiota is well-known; in contrast, the upper reproductive tract remains largely unexplored. Alteration in the uterine microbiota, which is dependent on the nutrients and hormones available to the uterus, is likely to play an important role in uterine-related diseases such as hysteromyoma, adenomyosis, and endometriosis. Uterine mucosa is an important tissue barrier whose main function is to offer protection against pathogens and other toxic factors, while maintaining a symbiotic relationship with commensal microbes. These characteristics are shared by all the mucosal tissues; however, the uterine mucosa is unique since it changes cyclically during the menstrual cycle as well as pregnancy. The immune system, besides its role in the defense process, plays crucial roles in reproduction as it ensures local immune tolerance to fetal/paternal antigens, trophoblast invasion, and vascular remodeling. The human endometrium contains a conspicuous number of immune cells, mainly Natural Killers (NK) cells, which are phenotypically distinct from peripheral cytotoxic NK, cells and macrophages. The endometrium also contains few lymphoid aggregates comprising B cell and CD8⁺ T cells. The number and the phenotype of these cells change during the menstrual cycle. It has become evident in recent years that the immune cell phenotype and function can be influenced by microbiota. Immune cells can sense the presence of microbes through their pattern recognition receptors, setting up host-microbe interaction. The microbiota exerts an appropriately controlled defense mechanism by competing for nutrients and mucosal space with pathogens. It has recently been considered that uterus is a non-sterile compartment since it seems to possess its own microbiota. There has been an increasing interest in characterizing the nature of microbial colonization within the uterus and its apparent impact on fertility and pregnancy. This review will examine the potential relationship between the uterine microbiota and the immune cells present in the local environment.

Role of Macrophages in Pregnancy and Related Complications

Macrophages (MФs) are the leukocytes produced from differentiation of monocytes and are located in almost all tissues of human body. They are involved in various processes, such as phagocytosis, innate and adaptive immunity, proinflammatory (M1) and anti-inflammatory (M2) activity, depending on the tissue microenvironment. They play a crucial role in pregnancy, and their dysfunction or alteration of polarity is involved in pregnancy disorders, like preeclampsia, recurrent spontaneous abortion, infertility, intrauterine growth restriction, and preterm labor. About 50-60% of decidual leukocytes are natural killer (NK) cells followed by MФs (the second largest population). MФs are actively involved in trophoblast invasion, tissue and vascular remodeling during early pregnancy, besides their role as major antigen-presenting cells in the decidua. These cells have different phenotypes and polarities in different stages of pregnancy. They have also been observed to enhance tumor growth by their anti-inflammatory activity (M2 type) and prevent immunogenic rejection. Targeted alteration of polarity (M1-M2 or vice versa) could be a major focus in the future treatment of pregnancy complications. This review is focused on the role of MФs in pregnancy, their involvement in pregnancy disorders, and decidual MФs as possible therapeutic targets for the treatment of pregnancy complications.