The development of endometriosis in a murine model is dependent on the presence of dendritic cells

Causal association of immune cells and endometriosis: a Mendelian randomization study

Objective

To investigate the causal effect of immune cells on endometriosis (EMS), we performed a Mendelian randomization analysis.

Methods

Mendelian randomization (MR) uses genetic variants as instrumental variables to investigate the causal effects of exposures on outcomes in observational data. In this study, we conducted a thorough two-sample MR analysis to investigate the causal relationship between 731 immune cells and endometriosis. We used complementary Mendelian randomization (MR) methods, including weighted median estimator (WME) and inverse variance weighted (IVW), and performed sensitivity analyses to assess the robustness of our results.

Results

Four immune phenotypes have been found to be significantly associated with the risk of developing EMS: B cell %lymphocyte (WME: OR: 1.074, p = 0.027 and IVW: OR: 1.058, p = 0.008), CD14 on Mo MDSC (WME: OR: 1.056, p =0.021 and IVW: OR: 1.047, p = 0.021), CD14+ CD16- monocyte %monocyte (WME: OR: 0.947, p = 0.024 and IVW: OR: 0.958, p = 0.011), CD25 on unsw mem (WME: OR: 1.055, p = 0.030 and IVW: OR: 1.048, p = 0.003). Sensitivity analyses confirmed the main findings, demonstrating consistency across analyses.

Conclusions

Our MR analysis provides compelling evidence for a direct causal link between immune cells and EMS, thereby advancing our understanding of the disease. It also provides new avenues and opportunities for the development of immunomodulatory therapeutic strategies in the future.

Understanding endometriosis from an immunomicroenvironmental perspective

ABSTRACT

Endometriosis, a heterogeneous, inflammatory, and estrogen-dependent gynecological disease defined by the presence and growth of endometrial tissues outside the lining of the uterus, affects approximately 5-10% of reproductive-age women, causing chronic pelvic pain and reduced fertility. Although the etiology of endometriosis is still elusive, emerging evidence supports the idea that immune dysregulation can promote the survival and growth of retrograde endometrial debris. Peritoneal macrophages and natural killer (NK) cells exhibit deficient cytotoxicity in the endometriotic microenvironment, leading to inefficient eradication of refluxed endometrial fragments. In addition, the imbalance of T-cell subtypes results in aberrant cytokine production and chronic inflammation, which contribute to endometriosis development. Although it remains uncertain whether immune dysregulation represents an initial cause or merely a secondary enhancer of endometriosis, therapies targeting altered immune pathways exhibit satisfactory effects in preventing disease onset and progression. Here, we summarize the phenotypic and functional alterations of immune cells in the endometriotic microenvironment, focusing on their interactions with microbiota and endocrine and nervous systems, and how these interactions contribute to the etiology and symptomology of endometriosis.

Peritoneal immune microenvironment of endometriosis: Role and therapeutic perspectives

Endometriosis, an estrogen-dependent chronic inflammatory disease characterized by the growth of endometrium-like tissues outside the uterine cavity, affects 10% of reproductive-age women. Although the pathogenesis of endometriosis is uncertain, it is widely accepted that retrograde menstruation results in ectopic endometrial tissue implantation. Given that not all women with retrograde menstruation develop endometriosis, immune factors have been hypothesized to affect the pathogenesis of endometriosis. In this review, we demonstrate that the peritoneal immune microenvironment, including innate immunity and adaptive immunity, plays a central role in the pathogenesis of endometriosis. Current evidence supports the fact that immune cells, such as macrophages, natural killer (NK) cells, dendritic cells (DCs), neutrophils, T cells, and B cells, as well as cytokines and inflammatory mediators, contribute to the vascularization and fibrogenesis of endometriotic lesions, accelerating the implantation and development of ectopic endometrial lesions. Endocrine system dysfunction influences the immune microenvironment through overexpressed estrogen and progesterone resistance. In light of the limitations of hormonal therapy, we describe the prospects for potential diagnostic biomarkers and nonhormonal therapy based on the regulation of the immune microenvironment. Further studies are warranted to explore the available diagnostic biomarkers and immunological therapeutic strategies for endometriosis.

Features of peritoneal dendritic cells in the development of endometriosis

BACKGROUND

Emerging evidence of immunological dysfunction have been described in endometriosis. Dendritic cells (DCs), one of the main antigen-presenting cells, are specialized in the initiation and modulation of the adaptive immune response. Emerging studies demonstrated both endometrial and circulating differences in DCs populations in women with endometriosis. However, the role and mechanism of peritoneal DCs in endometriosis is still unclear. The present study was undertaken to explore the features of peritoneal DCs in the pathogenesis of endometriosis. This study is beneficial to further clarify the cause of endometriosis and provide a new insight into the medical treatment for endometriosis.

METHODS

The study included 12 women with endometriosis and 11 women without endometriosis. The C57BL6 mouse model of endometriosis was established by intraperitoneal injection of endometrial segments. The peritoneal DCs of endometriosis patients and mouse models were analyzed by fluorescence associated cell sorting (FACS) examination.

RESULTS

Increased cell density of peritoneal DCs were observed in endometriosis patients. Moreover, the proportion of mature DCs (mDCs, CD80^highCD1a^low cells) in the peritoneal DCs was lower whereas the proportion of immature DCs (iDCs, CD80^lowCD1a^high cells) was increased in endometriosis patients. Similarly, the cell density of peritoneal DCs in murine models increased immediately after the injection of endometrial tissues and reached the highest level at 14 days. In addition, the proportion of mDCs (CD11c^highCD80^high cells) in the peritoneal DCs decreased immediately after the injection of endometrial tissues and then increased with the time until 42 days, but still lower than the control group. In contrast, the proportion of iDCs (CD11c^highCD80^low cells) in the peritoneal DCs showed the opposite dynamic changes. However, after treated with LPS, the mDCs proportion was significantly increased, leading to lower volume and weight of the endometriosis lesions.

CONCLUSIONS

Increased level of peritoneal DCs facilitated the pathogenesis of endometriosis lesions, especially in the early stage of the disease. Furthermore, peritoneal DCs maturation played an important role in the development of endometriosis.

Correlation between Endometriosis and Selected Allergic and Autoimmune Diseases and Eating Habits

Background and Objectives: Endometriosis is a hormone-dependent chronic inflammatory disease with serious reproductive and general health consequences. It is viewed as a multifactorial problem, consisting of matters related to altered immunity and genetics. In this study, we determined the correlation between endometriosis and allergic and autoimmune diseases in patients at reproductive age. Materials and Methods: Online surveys distributed through websites related to gynecological problems. The questionnaire was composed of 63 single and multiple-choice questions concerning the course of endometriosis, diet, and allergic and autoimmune diseases. The obtained data were assessed using statistical tests. Results: 501 female patients (mean age 31.1 SD = 6.8) were included in the study. The control group (n = 155) consisted of healthy females, whereas the study group (n = 346) consisted of female patients with endometriosis; each group was subdivided according to allergy status. There were statistically significant differences between groups for the following: positive family history of endometriosis (p = 0.0002), onset of allergic symptoms (p = 0.0003), frequency and duration of abdominal pain (p = 0.00625), and defecation disorders (p = 0.0006). Asthma was less common in the study group (p = 0.00611). The group of patients with endometriosis and allergies had a high median of consumption of red meat (p = 0.0143), fish (p = 0.0016), and dairy products (p = 0.0001). Conclusions: Endometriosis did not affect autoimmune diseases and their courses. Patients with diagnosed endometriosis presented allergy symptoms much earlier than the healthy patients. The consumption of dietary products such as soya products, red meat, and alcohol had an influence on the occurrence of endometriosis.

Endometriosis: A Disease with Few Direct Treatment Options

Endometriosis is a gynecological condition characterized by the growth of endometrium-like tissues inside and outside the pelvic cavity. The evolution of the disease can lead to infertility in addition to high treatment costs. Currently, available medications are only effective in treating endometriosis-related pain; however, it is not a targeted treatment. The objective of this work is to review the characteristics of the disease, the diagnostic means and treatments available, as well as to discuss new therapeutic options.

The Promises of Natural Killer Cell Therapy in Endometriosis

Endometriosis is a gynaecological disease defined by the growth of endometrium-like tissue outside the uterus. The disease is present in approximately 5–10% of women of reproductive age and causes pelvic pain and infertility. The pathophysiology is not completely understood, but retrograde menstruation and deficiency in natural killer (NK) cells that clear endometriotic cells in the peritoneal cavity play an important role. Nowadays, hormonal therapy and surgery to remove endometriosis lesions are used as treatment. However, these therapies do not work for all patients, and hormonal therapy prevents patients from getting pregnant. Therefore, new treatment strategies should be developed. Since the cytotoxicity of NK cells is decreased in endometriosis, we performed a literature search into the possibility of NK cell therapy. Available treatment options include the inhibition of receptor–ligand interaction for KIR2DL1, NKG2A, LILRB1/2, and PD-1/PD-L1; inhibition of TGF-β; stimulation of NK cells with IL-2; and mycobacterial treatment with BCG. In preclinical work, these therapies show promising results but unfortunately have side effects, which have not specifically been studied in endometriosis patients. Before NK cell treatment can be used in the clinic, more research is needed.

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

BACKGROUND

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

AIMS

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

CONTENT

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

IMPLICATIONS

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

The role of dendritic cells in endometriosis: A systematic review

Endometriosis (EDT), a common estrogen-dependent inflammatory disorder, is characterized by endometrial-like tissue outside the uterus. While its pathogenesis is poorly understood, it is supposed that the immune system plays a role in its pathophysiology, and increased number of immune cells and changes in both cell-mediated and humoral immunity have been described. Dendritic cells (DCs) are antigen-presenting cells (APC) of the immune system that recognize, capture, and process complex antigens and present them to T cells, conferring them a unique ability as mediators between the innate and adaptive immune systems. This systematic review aims to enlighten possible disturbances (systemically and locally) of DCs in the development and progression of endometriosis. A search using the strategy: ("dendritic cells" AND "immunology" AND "endometriosis") in databases resulted in 490 citations; after applying inclusion and exclusion criteria, a total of 13 studies were assessed. The evaluated studies demonstrated that DCs are susceptible to pro-endometriotic changes which could inhibit immature DCs (imDCs) from their maturation and induce imDCs into a macrophage phenotype. In addition, the growth and vascularization of endometriosis requires the presence of endogenous DC, which infiltrate endometriotic lesions and enhance endothelial cell migration by secreting proangiogenic factors. Whereas DC maturation suppresses this response, imDC actively promote angiogenesis and growth, leading to a switch in their immunologic role from presenting antigens to support angiogenesis and EDT progression.

Immunoregulation by type I interferons in the peritoneal cavity

The peritoneal cavity, a fluid-containing potential space surrounding the abdominal and pelvic organs, is home to a rich network of immune cells that maintain tissue homeostasis and provide protection against infection. However, under pathological conditions such as peritonitis, endometriosis, and peritoneal carcinomatosis, the peritoneal immune system can become dysregulated, resulting in nonresolving inflammation and disease progression. An enhanced understanding of the factors that regulate peritoneal immune cells under both homeostatic conditions and in disease contexts is therefore required to identify new treatment strategies for these often life-limiting peritoneal pathologies. Type I interferons (T1IFNs) are a family of cytokines with broad immunoregulatory functions, which provide defense against viruses, bacteria, and cancer. There have been numerous reports of immunoregulation by T1IFNs within the peritoneal cavity, which can contribute to both the resolution or propagation of peritoneal disease states, depending on the specifics of the disease setting and local environment. In this review, we provide an overview of the major immune cell populations that reside in the peritoneal cavity (or infiltrate it under inflammatory conditions) and highlight their contribution to the initiation, progression, or resolution of peritoneal diseases. Additionally, we will discuss the role of T1IFNs in the regulation of peritoneal immune cells, and summarize the results of laboratory studies and clinical trials which have investigated T1IFNs in peritonitis/sepsis, endometriosis, and peritoneal carcinomatosis.

A prominent environmental endocrine disruptor, 4-nonylphenol, promotes endometriosis development via plasmacytoid dendritic cells

Endometriosis is an estrogen-dependent chronic inflammatory disease and is associated etiologically with environmental endocrine disruptor (EED) exposure. 4-nonylphenol (NP), a widely found EED, has weak estrogenic activity and modulates plasmacytoid dendritic cell (pDC) function in vitro and in vivo. We aimed to elucidate the immunomodulatory effect of NP on the development of endometriosis, particularly focusing on pDCs. This study established a surgically induced endometriosis murine model (C57BL/6) under conditions of NP treatment that are relevant to the level and route of human exposure. Multi-parametric flow cytometry was used for analysis of infiltrated immune cell subsets in lesions. The results showed that NP exposure significantly promoted endometriotic lesion growth, survival and angiogenesis development of lesions as well as pDC accumulation in the lesions in mice. Adoptive transfer of NP-conditioned pDCs into mice significantly enhanced lesion development and local pDC infiltration, whereas NP-conditioned conventional dendritic cells did not affect lesion growth. In vitro functional analysis showed that NP-conditioned pDCs in lesions expressed high levels of CD36, a scavenger receptor and NP-conditioned splenic pDCs secreted an enhanced level of IL-10 in response to apoptotic cell recognition in a CD36-dependent manner. Furthermore, we observed that local treatment with blocking antibodies against IL-10 and CD36 on the day of surgery significantly inhibited lesion development. NP exposure also altered the estrous cycle in mice. The results suggest that chronic and low-dose exposure to NP enhances endometriotic lesion growth by altering pDC homeostasis and function. This study has important implications for understanding the environment-innate immunity interaction in human endometriosis.

n-Butyl Benzyl Phthalate Exposure Promotes Lesion Survival in a Murine Endometriosis Model

Endometriosis is an inflammatory and estrogen-dependent gynecological disease associated with exposure to environmental endocrine disruptors. n-Butyl benzyl phthalate (BBP), a ubiquitous plasticizer, has weak estrogenic activity, and exposure to BBP is associated with endometriosis. We aimed to elucidate the immunomodulatory effect of BBP on endometriosis development. We previously established a surgery-induced endometriosis-like murine model. In the present study, we exposed those mice to BBP 10 days prior to surgery and 4 weeks after surgery at physiologically relevant doses to mimic human exposure. Chronic exposure to BBP did not promote the growth of endometriotic lesions; however, the lesion survival rate in BBP-treated mice did increase significantly compared with control mice. Multiparametric flow cytometry showed that BBP exposure did not affect the homeostasis of infiltrated immune subsets in lesions but did enhance CD44 (adhesion marker) expression on plasmacytoid dendritic cells (pDCs). Blocking CD44 interactions locally inhibited endometriotic lesion growth. Immunofluorescence results further confirmed that CD44 blocking inhibited pDC infiltration and reduced the frequency of CD44⁺ pDCs in endometriotic tissues. BBP also disrupted the estrus cycle in these mice. This study suggests that chronic exposure to low-dose BBP may promote survival of endometriotic tissue through CD44-expressing pDCs.

Comprehensive analysis utilizing flow cytometry and immunohistochemistry reveals inflammatory changes in local endometrial and systemic dendritic cell populations in endometriosis

STUDY QUESTION

What are the detailed endometrial tissue specific and systemic dendritic cell (DC) subset disturbances in endometriosis?

SUMMARY ANSWER

This study confirms myeloid DC (mDC) and plasmacytoid DC subsets are readily identified in endometrial tissue and shows both endometrial and circulating differences in DC populations in women with endometriosis, with disease stage-specific relationships evident locally in the endometrium.

WHAT IS KNOWN ALREADY

Immune factors in the uterus, the peritoneal environment and systemically are implicated in the pathogenesis and progression of both endometriosis and infertility. While there is some evidence that endometrial DC populations are altered in endometriosis, DC subset involvement in both the endometrium and peripheral blood have not been comprehensively investigated so the functional consequences have been unknown.

STUDY DESIGN, SIZE, DURATION

This prospective cross-sectional cohort study compares circulating and endometrial DC populations in women of reproductive age with and without endometriosis (n = 55 and 30, respectively), wherein each participant donated samples at a single time point. Study participants were surveyed for menstrual cycle phase, American Society for Reproductive Medicine (ASRM) endometriosis disease stage and fertility status (where possible).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Peripheral blood samples were processed into mononuclear cells for analysis by flow cytometry, and endometrial samples were analysed by immunohistochemistry and dissociated into single-cell suspension for flow cytometry.

MAIN RESULTS AND THE ROLE OF CHANCE

In the endometrium of women with endometriosis, IRF-8+ cells were increased during the proliferative phase (P = 0.014), total DC proportions increased in the secretory phase (P = 0.038) and normal menstrual cyclical fluctuations in CD1c+ and IRF-8+ cells blunted; indicative of a consistently inflammatory tissue environment. The inflammatory changes in CD141+ and IRF-8+ populations in the endometrium of women with endometriosis were particularly evident in more advanced ASRM stages of the disease (respective P-values 0.032 and 0.045). There was also evidence of systemic inflammation in women with endometriosis, with increased circulating CD141+ mDC proportions (overall P = 0.040, secretory phase P = 0.021).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

As is common in this type of study, one of the main limitations was small sample numbers, particularly during the menstrual phase of the cycle.

WIDER IMPLICATIONS OF THE FINDINGS

Further phenotyping of local and circulating immune cell subtypes is critical to improving understanding of endometriosis pathogenesis and immune contributions to infertility associated with the disease.

STUDY FUNDING/COMPETING INTEREST(S)

This research was financially supported by a Sydney Medical School and Balnaves Foundation Kick Start Grant and the Department of Obstetrics, Gynaecology and Neonatology at The University of Sydney. The authors have no conflicts of interest to declare.

RNA sequencing-based long non-coding RNA analysis and immunoassay in ovarian endometriosis

PROBLEM

The mechanism underlying endometriosis is currently unknown. However, studies have indicated that immunity plays an important role in endometriosis occurrence and development. Long non-coding RNAs (lncRNAs) do not encode proteins but participate in a variety of biological processes via different mechanisms. This study investigated differences in immune cells and immune-related lncRNAs via high-throughput RNA sequencing (RNA-seq) analysis of ectopic and eutopic endometria with endometriosis.

METHOD OF STUDY

RNA-seq was performed in six pairs of ectopic and eutopic endometria samples, and real-time quantitative polymerase chain reaction was used to verify the results of RNA-seq for 30 pairs of samples. Different immune cell types were identified based on the RNA-seq results, using ImmuCellAI. Immune-related lncRNAs were obtained by analyzing immune-related genes from the ImmPort Database and RNA-seq results.

RESULTS

A total of 952 differentially expressed lncRNAs were identified, of which 446 were immune-related. The ectopic and eutopic endometrium could easily be distinguished in the principal component analysis of immune-related lncRNAs. Analysis of 24 immune cell types revealed the differential abundance of 13 types. Sixty immune-related mRNAs were associated with the top 20 dysregulated immune-related lncRNAs, 11 of which were transcripts of immune cell marker genes.

CONCLUSIONS

Our data indicated that a variety of dysregulated lncRNAs were associated with immunity, and these may provide a basis for future immune-related endometriosis research.

Toll-Like Receptor 2 Expression as a New Hallmark of Advanced Endometriosis

Recent evidence suggests that immunological aspects play a pivotal role in this disorder. Toll-like receptor 2 (TLR2) is crucial in recognizing microbial infections and mediating innate immune response. The objective of our study was to rate with flow cytometry the levels of several subsets of dendritic cells, monocytes, and basic peripheral blood lymphocytes expressing TLR2, aiming at the determination of a possible correlation between the expression of TLR2 and the clinical outcomes of endometriosis in 40 patients and 40 age-matched healthy women. Our study showed the importance of TLR2 expression, mainly on myeloid dendritic cells (mDCs) and B cells in patients with endometriosis. Both mDCs BDCA1+CD19-TLR2+ and B lymphocytes CD19+TLR-2+ proved useful in the differentiation of affected individuals with stages 3–4 of the disease (area under the receiver operating characteristic curve /AUC/ = 0.96, p < 0.0001 for mDCs; AUC = 0.78, p = 0.0001 for B lymphocytes), and those presenting adhesion (AUC = 0.92, p < 0.0001 for mDCs; AUC = 0.82, p < 0.0001 for B lymphocytes) or infertility (AUC = 0.83, p < 0.0001 for mDCs; AUC = 0.73, p = 0.006 for B lymphocytes). Our findings suggest that the levels of TLR2-expressing cells, particularly mDCs and B lymphocytes, may be an effective biomarker of endometriosis, because the disease currently lacks clinically useful noninvasive biomarkers enabling early and cost-effective diagnosis.

Possible involvement of crosstalk between endometrial cells and mast cells in the development of endometriosis via CCL8/CCR1

BACKGROUND

The density and the activity of mast cells are associated with endometriosis. However, the role of mast cells on the pathogenesis of endometriosis remains unclear. Our study aims to investigate whether endometrial cells interact with mast cells and the involvement of their crosstalk in the development of endometriosis.

METHODS

The transwell assay was applied to investigate the effect of mast cells on the migratory ability of human primary endometrial cells. Mast cells were cocultured with endometrial epithelial and stromal cells respectively and total RNAs were isolated and subjected to mRNA sequencing. Next, the transwell assay, CCK-8, and tube formation were applied to study the role of CCL8 on the endometrial and endothelial cells in vitro. The mouse model was also established to confirm the role of CCL8 in the development and angiogenesis of endometriosis.

RESULTS

CCL8 was up-regulated in mast cells when cocultured with endometrial cells. CCL8 was highly expressed in the ectopic endometrium and the serum of patients with endometriosis. CCL8 promoted the migratory ability of endometrial epithelial and stromal cells and increased the proliferation, migration, and tube formation of endothelial cells. CCR1, the receptor of CCL8, was over-expressed in the ectopic endometrium and colocalized with blood vessels in ovarian endometriomas. The inhibition of CCR1 suppressed the development and angiogenesis of endometriosis in vivo.

CONCLUSION

The crosstalk between endometrial cells and mast cells in the development of endometriosis via CCL8/CCR1 was demonstrated, thereby providing a new treatment strategy for endometriosis.

Endometriosis-associated ovarian cancer: What have we learned so far?

Endometriosis is defined as the presence of ectopic endometrial tissue outside of the uterine cavity, most commonly in the ovaries and peritoneum. It is a complex disease that is influenced by multiple factors. It is also a common gynecological disorder and affects approximately 10-15% of all women of reproductive age. Recent molecular and pathological studies indicate that endometriosis may serve as a precursor of ovarian cancer (endometriosis-associated ovarian cancer, EAOC), particularly endometrioid and clear cell ovarian cancers. Although histological and epidemiological studies have demonstrated that endometriosis has a malignant potential, the molecular mechanism that underlies the malignant transformation of endometriosis is still controversial, and the precise mechanism of carcinogenesis must be fully elucidated. Currently, the development and improvement of a new sequencing technology, next-generation sequencing (NGS), has been increasingly relevant in cancer genomics research. Recently, NGS has also been utilized in clinical oncology to advance the personalized treatment of cancer. In addition, the sensitivity, speed, and cost make NGS a highly attractive platform compared to other sequencing modalities. For this reason, NGS may lead to the identification of driver mutations and underlying pathways associated with EAOC. Here, we present an overview of the molecular pathways that have led to the current opinions on the relationship between endometriosis and ovarian cancer.

The link between immunity, autoimmunity and endometriosis: a literature update

Endometriosis (EMS), an estrogen-dependent inflammatory disorder affects approximately 5-10% of the general female population of reproductive age and 20-90% of women with pelvic pain and infertility. Many immunological factors are known to contribute significantly to the pathogenesis and pathophysiology of EMS, and both chronic local inflammation and autoantibodies in EMS shares many similarities with autoimmune diseases (AD). However, the autoimmune etiology in EMS remains controversial, and its evidence on autoimmune basis may be limited. Here we aim to review the current understanding between autoimmunity and EMS to provide important knowledge to develop future potential immunomodulatory therapy for the treatment of EMS.

The Immunopathophysiology of Endometriosis

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

Basic mechanisms of vascularization in endometriosis and their clinical implications

BACKGROUND

Vascularization is a major hallmark in the pathogenesis of endometriosis. An increasing number of studies suggests that multiple mechanisms contribute to the vascularization of endometriotic lesions, including angiogenesis, vasculogenesis and inosculation.

OBJECTIVE AND RATIONALE

In this review, we provide an overview of the basic mechanisms of vascularization in endometriosis and give special emphasis on their future clinical implications in the diagnosis and therapy of the disease.

SEARCH METHODS

Literature searches were performed in PubMed for English articles with the key words 'endometriosis', 'endometriotic lesions', 'angiogenesis', 'vascularization', 'vasculogenesis', 'endothelial progenitor cells' and 'inosculation'. The searches included both animal and human studies. No restriction was set for the publication date.

OUTCOMES

The engraftment of endometriotic lesions is typically associated with angiogenesis, i.e. the formation of new blood vessels from pre-existing ones. This angiogenic process underlies the complex regulation by angiogenic growth factors and hormones, which activate intracellular pathways and associated signaling molecules. In addition, circulating endothelial progenitor cells (EPCs) are mobilized from the bone marrow and recruited into endometriotic lesions, where they are incorporated into the endothelium of newly developing microvessels, referred to as vasculogenesis. Finally, preformed microvessels in shed endometrial fragments inosculate with the surrounding host microvasculature, resulting in a rapid blood supply to the ectopic tissue. These vascularization modes offer different possibilities for the establishment of novel diagnostic and therapeutic approaches. Angiogenic growth factors and EPCs may serve as biomarkers for the diagnosis and classification of endometriosis. Blood vessel formation and mature microvessels in endometriotic lesions may be targeted by means of anti-angiogenic compounds and vascular-disrupting agents.

WIDER IMPLICATIONS

The establishment of vascularization-based approaches in the management of endometriosis still represents a major challenge. For diagnostic purposes, reliable angiogenic and vasculogenic biomarker panels exhibiting a high sensitivity and specificity must be identified. For therapeutic purposes, novel compounds selectively targeting the vascularization of endometriotic lesions without inducing severe side effects are required. Recent progress in the field of endometriosis research indicates that these goals may be achieved in the near future.

Involvement of immune cells in the pathogenesis of endometriosis

Endometriosis is characterized by the implantation and growth of endometriotic tissues outside the uterus. It is widely accepted the theory that endometriosis is caused by the implantation of endometrial tissue from retrograde menstruation; however, retrograde menstruation occurs in almost all women and other factors are required for the establishment of endometriosis, such as cell survival, cell invasion, angiogenesis, and cell growth. Immune factors in the local environment may, therefore, contribute to the formation and progression of endometriosis. Current evidence supports the involvement of immune cells in the pathogenesis of endometriosis. Peritoneal neutrophils and macrophages secrete biochemical factors that help endometriotic cell growth and invasion, and angiogenesis. Peritoneal macrophages and NK cells in endometriosis have limited capability of eliminating endometrial cells in the peritoneal cavity. An imbalance of T cell subsets leads to aberrant cytokine secretions and inflammation that results in the growth of endometriosis lesions. It is still uncertain whether these immune cells have a role in the initial cause and/or stimulate actions that enhance disease; however, in either case, modulating the actions of these cells may prevent initiation or disease progression. Further studies are needed to deepen the understanding of the pathology of endometriosis and to develop novel management approaches of benefit to women suffering from this disease.

Decreased Cytotoxicity of Peripheral and Peritoneal Natural Killer Cell in Endometriosis

Endometriosis causes significant chronic pelvic pain, dysmenorrhea, and infertility and affects 10% of all women. In endometriosis, ectopic endometrium surviving after retrograde menstruation exhibits an abnormal immune response characterized by increased levels of activated macrophages and inflammatory cytokines. Particularly, dysfunctional natural killer (NK) cells play an important role in the pathogenesis of the disease by either facilitating or inhibiting the survival, implantation, and proliferation of endometrial cells. NK cells in the peritoneum and peritoneal fluid exhibit reduced levels of cytotoxicity in women with endometriosis. Several cytokines and inhibitory factors in the serum and peritoneal fluid also dysregulate NK cell cytotoxicity. Additionally, increased numbers of immature peripheral NK cells and induction of NK cell apoptosis are evident in the peritoneal fluid of women with endometriosis. The high rate of endometriosis recurrence after pharmaceutical or surgical treatment, which is associated with dysfunctional NK cells, indicates that new immunomodulatory management strategies are required. A good understanding of immune dysfunction would enable improvement of current treatments for endometriosis.

Pathophysiology and Immune Dysfunction in Endometriosis

Endometriosis is an estrogen-dependent, chronic, proinflammatory disease prevalent in 10% of women of reproductive age worldwide. Characterized by the growth of endometrium-like tissue in aberrant locations outside of the uterus, it is responsible for symptoms including chronic pelvic pain, dysmenorrhea, and subfertility that degrade quality of life of women significantly. In Canada, direct and indirect economic cost of endometriosis amounts to 1.8 billion dollars, and this is elevated to 20 billion dollars in the United States. Despite decades of research, the etiology and pathophysiology of endometriosis still remain to be elucidated. This review aims to bring together the current understanding regarding the pathogenesis of endometriosis with specific focus on mechanisms behind vascularization of the lesions and the contribution of immune factors in facilitating lesion establishment and development. The role of hormones, immune cells, and cytokine signaling is highlighted, in addition to discussing the current pharmaceutical options available for management of pain symptoms in women with endometriosis.

Gonadotropin stimulation in mice leads to ovarian accumulation of immature myeloid cells and altered expression of proangiogenic genes

OBJECTIVE

Ovarian hyperstimulation syndrome is associated with increased angiogenesis and vascular leakage. Immature myeloid cells (IMCs) and dendritic cells have been shown to be actively involved in angiogenesis in several disease models in mice and humans. Nevertheless, little is known about the role of these cells in the ovary. As such, this study sought to determine whether alterations in these ovarian myeloid cell populations are associated with gonadotropin stimulation in a mouse model.

STUDY DESIGN

Four-week-old pre-pubertal C57Bl/6 female mice were allocated into three groups: high-dose stimulation (n=4; pregnant mare serum gonadotropins (PMSG) 20U for 2 days), low-dose stimulation (n=5; PMSG 5U for 1 day) and sham-treated controls (n=4). Human chorionic gonadotropin 5U was injected on Day 3, and the mice were killed on Day 5. Ovaries were analysed by flow cytometry, confocal microscopy and quantitative polymerase chain reaction.

RESULTS

Gonadotropin stimulation increased the proportion of CD11b(+)Gr1(+) IMCs among the ovarian myeloid cells: 22.6±8.1% (high dose), 7.2±1.6% (low dose) and 4.1±0.3% (control) (p=0.02). Conversely, gonadotropin stimulation decreased the proportion of ovarian CD11c(+)MHCII(+) dendritic cells: 15.1±1.9% (high dose), 20.7±4.8% (low dose) and 27.3±8.2% (control) (p=0.02). IMCs, unlike dendritic cells, were localized adjacent to PECAM1(+) endothelial cells. Finally, gonadotropin stimulation was associated with increased expression of S100A8, S100A9, Vcan and Dmbt1, and decreased expression of MMP12.

CONCLUSIONS

Gonadotropin stimulation is associated with proangiogenic myeloid cell alterations, reflected by a dose-dependent increase in ovarian IMCs and a parallel decrease in dendritic cells. Recruited IMCs localize strategically at sites of angiogenesis. These changes are associated with differential expression of key proangiogenic genes.