The expressions of CD200 and CD200R molecules on myeloid and lymphoid dendritic cells in pre-eclampsia and normal pregnancy

Dendritic Cells and the Establishment of Fetomaternal Tolerance for Successful Human Pregnancy

Pregnancy is a remarkable event where the semi-allogeneic fetus develops in the mother's uterus, despite genetic and immunological differences. The antigen handling and processing at the maternal-fetal interface during pregnancy appear to be crucial for the adaptation of the maternal immune system and for tolerance to the developing fetus and placenta. Maternal antigen-presenting cells (APCs), such as macrophages (Mφs) and dendritic cells (DCs), are present at the maternal-fetal interface throughout pregnancy and are believed to play a crucial role in this process. Despite numerous studies focusing on the significance of Mφs, there is limited knowledge regarding the contribution of DCs in fetomaternal tolerance during pregnancy, making it a relatively new and growing field of research. This review focuses on how the behavior of DCs at the maternal-fetal interface adapts to pregnancy's unique demands. Moreover, it discusses how DCs interact with other cells in the decidual leukocyte network to regulate uterine and placental homeostasis and the local maternal immune responses to the fetus. The review particularly examines the different cell lineages of DCs with specific surface markers, which have not been critically reviewed in previous publications. Additionally, it emphasizes the impact that even minor disruptions in DC functions can have on pregnancy-related complications and proposes further research into the potential therapeutic benefits of targeting DCs to manage these complications.

Cellular immune responses in the pathophysiology of preeclampsia

Preeclampsia, defined as new-onset hypertension accompanied by proteinuria occurring at 20 weeks of gestation or later, is a leading cause of perinatal morbidity and mortality worldwide. The pathophysiology of this major multi-systemic syndrome includes defective deep placentation, oxidative stress, endothelial dysfunction, the presence of an anti-angiogenic state, and intravascular inflammation, among others. In this review, we provide a comprehensive overview of the cellular immune responses involved in the pathogenesis of preeclampsia. Specifically, we summarize the role of innate and adaptive immune cells in the maternal circulation, reproductive tissues, and at the maternal-fetal interface of women affected by this pregnancy complication. The major cellular subsets involved in the pathogenesis of preeclampsia are regulatory T cells, effector T cells, NK cells, monocytes, macrophages, and neutrophils. We also summarize the literature on those immune cells that have been less characterized in this clinical condition, such as γδ T cells, invariant natural killer T cells, dendritic cells, mast cells, and B cells. Moreover, we discuss in vivo studies utilizing a variety of animal models of preeclampsia to further support the role of immune cells in this disease. Finally, we highlight the existing gaps in knowledge of the immunobiology of preeclampsia that require further investigation. The goal of this review is to promote translational research leading to clinically relevant strategies that can improve adverse perinatal outcomes resulting from the obstetrical syndrome of preeclampsia.

Regulation of the innate immune cells during pregnancy: An immune checkpoint perspective

The foetus can be regarded as a half‐allograft implanted into the maternal body. In a successful pregnancy, the mother does not reject the foetus because of the immune tolerance mechanism at the maternal‐foetal interface. The innate immune cells are a large part of the decidual leukocytes contributing significantly to a successful pregnancy. Although the contributions have been recognized, their role in human pregnancy has not been completely elucidated. Additionally, the accumulated evidence demonstrates that the immune checkpoint molecules expressed on the immune cells are co‐inhibitory receptors regulating their activation and biological function. Therefore, it is critical to understand the immune microenvironment and explore the function of the innate immune cells during pregnancy. This review summarizes the classic immune checkpoints such as PD‐1, CTLA‐4 and some novel molecules recently identified, including TIM‐3, CD200, TIGIT and the Siglecs family on the decidual and peripheral innate immune cells during pregnancy. Furthermore, it emphasizes the role of the immune checkpoint molecules in pregnancy‐associated complications and reproductive immunotherapy.

SARS-CoV-2 Infection in Pregnant Women: Neuroimmune-Endocrine Changes at the Maternal-Fetal Interface

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has devastating effects on the population worldwide. Given this scenario, the extent of the impact of the disease on more vulnerable individuals, such as pregnant women, is of great concern. Although pregnancy may be a risk factor in respiratory virus infections, there are no considerable differences regarding COVID-19 severity observed between pregnant and nonpregnant women. In these circumstances, an emergent concern is the possibility of neurodevelopmental and neuropsychiatric harm for the offspring of infected mothers. Currently, there is no stronger evidence indicating vertical transmission of SARS-CoV-2; however, the exacerbated inflammatory response observed in the disease could lead to several impairments in the offspring's brain. Furthermore, in the face of historical knowledge on possible long-term consequences for the progeny's brain after infection by viruses, we must consider that this might be another deleterious facet of COVID-19. In light of neuroimmune interactions at the maternal-fetal interface, we review here the possible harmful outcomes to the offspring brains of mothers infected by SARS-CoV-2.

Dendritic cells in pregnancy and pregnancy-associated diseases

Dendritic cells (DCs) play a critical immuno-modulating role in pregnancy, which requires the maternal immune system to tolerate semiallogeneic fetus and at the same time to maintain adequate defense against pathogens. DCs interact closely with other immune components such as T cells, natural killer cells and macrophages, as well as the endocrine system to keep a pregnancy-friendly environment. Aberrant DC activities have been related to various pregnancy-associated diseases such as recurrent spontaneous abortion, preterm birth, pre-eclampsia, peripartum cardiomyopathy and infectious pregnancy complications. These findings make DCs an attractive candidate for prevention or therapy on the pregnancy-associated diseases. Here, we review recent findings that provide new insights into the roles of DCs in pregnancy and the related diseases. We also discuss the medical potentials to manipulate DCs in clinics. Whereas this is an emerging area with much work remaining, we anticipate that a better understanding of the role of DCs in maternal-fetal immunotolerance and a therapeutic manipulation of DCs will help women suffering from the pregnancy-associated diseases.

The CD200/CD200R signaling pathway contributes to spontaneous functional recovery by enhancing synaptic plasticity after stroke

BACKGROUND

Spontaneous functional recovery occurs during the acute phase after stroke onset, but this intrinsic recovery remains limited. Therefore, exploring the mechanism underlying spontaneous recovery and identifying potential strategies to promote functional rehabilitation after stroke are very important. The CD200/CD200R signaling pathway plays an important role in neurological recovery by modulating synaptic plasticity during multiple brain disorders. However, the effect and mechanism of action of the CD200/CD200R pathway in spontaneous functional recovery after stroke are unclear.

METHODS

In this study, we used a transient middle cerebral artery occlusion (MCAO) model in rats to investigate the function of CD200/CD200R signaling in spontaneous functional recovery after stroke. We performed a battery of behavioral tests (Longa test, adhesive removal test, limb-use asymmetry test, and the modified grip-traction test) to evaluate sensorimotor function after intracerebroventricular (i.c.v.) injection with CD200 fusion protein (CD200Fc) or CD200R blocking antibody (CD200R Ab) post-stroke. Density and morphology of dendritic spines were analyzed by Golgi staining. Microglia activation was evaluated by immunofluorescence staining. Western blot was used to detect the levels of protein and the levels of mRNA were measured by qPCR.

RESULTS

Our study demonstrated that sensorimotor function, synaptic proteins, and structures were gradually recovered and CD200R was transiently upregulated in ipsilateral cortex after stroke. Synapse-related proteins and dendritic spines were preserved, accompanied by sensorimotor functional recovery, after stereotaxic CD200Fc injection post-stroke. In addition, CD200Fc restrained microglia activation and pro-inflammatory factor release (such as Il-1, Tnf-α, and Il-6) after MCAO. On the contrary, CD200R Ab aggravated sensory function recovery in adhesive removal test and further promoted microglia activation and pro-inflammatory factor release (such as Il-1) after MCAO. The immune-modulatory effect of CD200/CD200R signaling might be exerted partly by its inhibition of the MAPK pathway.

CONCLUSIONS

This study provides evidence that the CD200/CD200R signaling pathway contributes to spontaneous functional recovery by enhancing synaptic plasticity via inhibition of microglia activation and inflammatory factor release.

Decreased expression of CD200 and CD200R1 by human decidual tissues in spontaneous early abortion

Objective: To examine the cellular distribution and the expression of CD200 and its receptor 1 (CD200R1) in human deciduas in first-trimester pregnant women with spontaneous early abortion (SEA) and normal pregnancy, and to explore their role in the etiology of SEA.Subjects and methods: Thirty-five women at 6-10-week gestation with SA and 30 women of similar gestational age with a healthy pregnancy were recruited. Expression of CD200 and CD200R1 in the deciduas was determined using immunohistochemistry, confocal laser scanning microscope, Western blot, and real-time PCR (RT-PCR).Results: The decidual stromal cells, glandular epithelial cells, and vessel endothelial cells during the first trimester of pregnancy express both CD200 and CD200R1 proteins. During this period, the expression of CD200 in glandular epithelial cells and vessel endothelial cells is significantly higher in normal pregnancy than that in women with SEA (0.3079 ± 0.0674 versus 0.2735 ± 0.0515; 0.4077 ± 0.1366 versus 0.3249 ± 0.0993); the expression of CD200R1 in stromal cells, decidual stromal cells, glandular epithelial cells is significantly higher during normal pregnancy than SEA (0.2574 ± 0.0588 versus 0.2292 ± 0.0415; 0.3617 ± 0.1046 versus 0.2804 ± 0.0640). Western blot analysis showed an approximately 44% decrease in CD200R1expression in decidua in the SEA versus the controls. Finally, in decidua, the expression of both CD200 protein and CD200R1 transcript are significantly higher in healthy first-trimester pregnancy than in SEA (CD200: 2.2089 ± 1.2754 versus 0.7241 ± 0.2143; CD200R1: 15.7843 ± 10.7085 versus 7.3381 ± 5.8529).Conclusions: Women with SEA have a lower level of CD200 and CD200R1 expression in deciduas compared with normal pregnant women suggesting that under physiological conditions, CD200 and CD200R1 expression by deciduas is important to prevent fetal loss ensure a successful pregnancy.

Reduced CD200 expression is associated with altered Th1/Th2 cytokine production in placental trophoblasts from preeclampsia

PROBLEM

To determine if altered trophoblast CD200 and CD200R expressions promote inflammatory cytokine production in preeclamptic placentas.

METHODS OF STUDY

Placental tissue CD200 and CD200R expressions were determined by immunostaining. Tissue sections from first-, second-, and third-trimester, normal term, and preeclamptic placentas were used. CD200 and CD200R expressions and cytokine production of TNFα, sTNFR1, INFγ, IL-4, IL-6, IL-8, and IL-10 were determined in trophoblasts from normal and preeclamptic placentas and in normal trophoblasts transfected with CD200 siRNA.

RESULTS

CD200, but not CD200R, expression was significantly reduced in trophoblasts from preeclamptic compared to normal placentas. Trophoblast from preeclamptic placentas and trophoblast transfected with CD200 siRNA produced significantly more TNFα, sTNFR1, IL-6, and IL-8, but significantly less IL-10, than trophoblasts from normal control placentas.

CONCLUSION

Downregulation of CD200 expression resulted in an imbalance of increased Th1 cytokine and decreased Th2 cytokine production in placental trophoblasts in preeclampsia.

An immune clock of human pregnancy

Themaintenance of pregnancy relies on finely tuned immune adaptations.We demonstrate that these adaptations are precisely timed, reflecting an immune clock of pregnancy in women delivering at term. Using mass cytometry, the abundance and functional responses of allmajor immune cell subsets were quantified in serial blood samples collected throughout pregnancy. Cell signaling–based Elastic Net, a regularized regressionmethod adapted from the elastic net algorithm, was developed to infer and prospectively validate a predictive model of interrelated immune events that accurately captures the chronology of pregnancy. Model components highlighted existing knowledge and revealed previously unreported biology, including a critical role for the interleukin-2–dependent STAT5ab signaling pathway in modulating T cell function during pregnancy. These findings unravel the precise timing of immunological events occurring during a term pregnancy and provide the analytical framework to identify immunological deviations implicated in pregnancy-related pathologies.

Association of peripheral blood dendritic cells with recurrent pregnancy loss: a case-controlled study

PROBLEM

Dendritic cells (DCs) have been reported to play an important role in pregnancy. However, the role of DCs in recurrent pregnancy loss (RPL) has not been investigated well.

METHOD OF STUDY

Forty-three women affected by RPL and 16 fertile controls were recruited from June 2013 to December 2014. The peripheral blood DCs subsets, including myeloid DCs (mDCs) and plasmacytoid DCs (pDCs), the levels (%) of CD80(+) , CD86(+) , and CD200(+) DCs were analyzed using flow cytometry.

RESULTS

The levels of total DCs, mDCs, and CD86(+) DCs were significantly higher (all P<.05); however, the level of CD200(+) DCs in the RPL group was significantly lower than that of the control group (P<.05). The logistical regression analyses showed that the elevated level of mDCs was significantly associated with RPL after adjustment for age (OR: 1.14, 95% CI, 1.01-1.29, P<.05).

CONCLUSION

The elevated level of mDCs was significantly associated with RPL, which might lead to the intervention of targeted immunosuppression in women with RPL.

Reduced Dendritic Cells Expressing CD200R1 in Children with Inflammatory Bowel Disease: Correlation with Th17 and Regulatory T Cells

Loss of tolerance of the adaptive immune system towards indigenous flora contributes to the development of inflammatory bowel diseases (IBD). Defects in dendritic cell (DC)-mediated innate and adoptive immune responses are conceivable. The aim of this study was to investigate the expression of the inhibitory molecules CD200R1 and their ligand CD200 on DCs, to clarify the role of the DCs in the pathogenesis of IBD. Thirty-seven pediatric IBD patients (23 with Crohn’s disease (CD) and 14 with ulcerative colitis (UC)) with mean age 13.25 ± 2.9 years were included. Fourteen age-matched healthy pediatric volunteers (five males and nine females) served as a control group (HC). The percentage of CD11c⁺ myeloid dendritic cells (mDCs) and CD123⁺ plasmacytoid DCs (pDCs) expressing CD200R1 and CD200 were evaluated in peripheral blood using flow cytometry and were correlated with routine biochemical, serological markers, serum levels of cytokines and with the percentages of circulating regulatory T cells (Treg) and CD4⁺ producing IL-17 (Th17). IBD patients showed a significant decrease in the percentage of pDCs and mDCs expressing CD200R1 compared to that of HC. Patients with UC showed increased expressions of the CD200 molecule on pDCs as compared to HC. DCs expressing CD200R1 were found to be correlated positively with Treg and negatively with TH17 and erythrocyte sedimentation rate (ESR). Our findings suggest that IBD is associated with dysregulation in the CD200R1/CD200 axis and that the decrease in DCs expressing CD200R1 may contribute to the imbalance of Th17 and Treg cells and in the pathogenesis of IBD.

Peripheral Dendritic Cells and CD4+CD25+Foxp3+ Regulatory T Cells in the First Trimester of Normal Pregnancy and in Women with Recurrent Miscarriage

The development of pregnancy is possible due to initiation of immune response in the body of the mother resulting in immune tolerance. Miscarriage may be caused by the impaired maternal immune response to paternal alloantigens located on the surface of trophoblast and fetal cells. The aim of the study was to compare the population of circulating dendritic cells (DCs) and CD4+CD25+Foxp3+ regulatory T cells (TREGs) in the first trimester of a normal pregnancy and in women with recurrent miscarriage and an attempt to determine the relationship between these cells and the role they may play in human reproductive failures. The study was conducted in a group of 33 first trimester pregnant women with recurrent miscarriage and in a group of 20 healthy pregnant women in the first trimester of normal pregnancy. Among mononuclear cells isolated from peripheral blood, the populations of DCs and TREGs were assessed by flow cytometry. The percentage of myeloid DCs and lymphoid DCs showed no significant difference between study and control group. Older maternal age and obesity significantly reduced the pool of circulating myeloid and lymphoid DCs (R=-0.39, p=0.02). In miscarriages the percentage of circulating TREGs was significantly lower compared to normal pregnancies (p=0.003). Among the analysed factors the percentage of TREGs was the most sensitive and the most specific parameter which correlated with the pregnancy loss. The reduction in the population of circulating TREGs suggests immunoregulatory mechanisms disorder in a pregnancy complicated by miscarriage.

Reduced CD200 and CD200R1 expression in human chorionic villi contributes to early spontaneous abortion

OBJECTIVE

To examine the expression of CD200 and its receptor (CD200R) in human chorionic villi during the first trimester of normal pregnancy and early spontaneous abortion (ESA).

DESIGN

Prospective study.

METHODS

Expression of CD200 and CD200R in the chorionic villi was determined using streptavidin-peroxidase immunohistochemistry, confocal laser scanning microscopy and real-time polymerase chain reaction.

POPULATION

Thirty-five women diagnosed with ESA and 30 women experiencing a healthy pregnancy in a medical university hospital in China were enrolled in this study between 2011 and 2013.

MAIN OUTCOME MEASURES

CD200 and CD200R expression.

RESULTS

The expression of CD200 in syncytiotrophoblast cells was significantly higher during normal pregnancy than in ESA (0.51 ± 0.05 vs. 0.35 ± 0.05). In contrast, expression of CD200 in cytotrophoblast cells and CD200R in stromal cells was significantly lower during normal pregnancy when compared with ESA (CD200: 0.16 ± 0.02 vs. 0.32 ± 0.03; CD200R: 0.19 ± 0.03 vs. 0.22 ± 0.02). In villi, the expression of both CD200 protein and CD200R transcripts were significantly higher in healthy first-trimester pregnancy than in ESA (CD200: 156.89 ± 105.65 vs. 37.51 ± 17.62).

CONCLUSIONS

There is an increase in inhibitory properties of human chorionic villi during normal pregnancy. The mechanism underlying ESA might be associated with enhanced expression of CD200 and CD200R in the trophoblast, leading to an upregulation of the immune response during the first trimester of pregnancy.

Liaison between natural killer cells and dendritic cells in human gestation

A successful pregnancy relies on immunological adaptations that allow the fetus to grow and develop in the uterus, despite being recognized by maternal immune cells. Among several immunocompetent cell types present within the human maternal/fetal interface, DC-SIGN(+) dendritic cells (DCs) and CD56(+) natural killer (NK) cells are of major importance for early pregnancy maintenance, not only generating maternal immunological tolerance but also regulating stromal cell differentiation. Previous reports show the presence of NK-DC cell conjugates in first trimester human decidua, suggesting that these cells may play a role in the modulation of the local immune response within the uterus. While effective immunity is necessary to protect the mother from harmful pathogens, some form of tolerance must be activated to avoid an immune response against fetal antigens. This review article discusses current evidence concerning the functions of DC and NK cells in pregnancy and their liaison in human decidua.

Amniotic fluid CD200 levels in pregnancies complicated by preterm prelabor rupture of the membranes

OBJECTIVE

To determine the amniotic fluid CD200 levels in uncomplicated pregnancies and in preterm prelabor rupture of the membranes (PPROM) according to microbial invasion of the amniotic cavity and histological chorioamnionitis and its association with neonatal outcomes.

METHODS

One hundred and fifty-nine women with singleton pregnancies were included in this study. Amniotic fluid was collected, and CD200 levels were determined using ELISA.

RESULTS

No difference was found in CD200 levels between women in the second trimester and women at term without labor. Women at term with labor had higher CD200 levels than women in the second trimester and women at term without labor. The presence of funisitis in PPROM pregnancies was associated with higher CD200 levels independent of gestational age (with funisitis: median 197.5 pg/mL versus without funisitis: median 61.0 pg/mL; p = 0.003). The need for tracheal intubation and the development of bronchopulmonary dysplasia were associated with higher CD200 levels.

CONCLUSIONS

Amniotic fluid CD200 levels remained stable in advanced pregnancy and they were increased during parturition. Elevated CD200 levels in the presence of funisitis suggest the involvement of negative regulatory mechanisms of innate immunity. CD200 may play a role in the development of pulmonary aspects of neonatal morbidity.

The Placenta in Toxicology. Part II

During pregnancy, the maternal immune system is challenged by the semiallogeneic fetus, which must be tolerated without compromising fetal or maternal health. This review updates the systemic and local immune changes taking place during human pregnancy, including some examples in rodents. Systemic changes are induced by contact of maternal blood with placental factors and include enhanced innate immunity with increased activation of granulocytes and nonclassical monocytes. Although a bias toward T helper (Th2) and regulatory T cell (Treg) immunity has been associated with healthy pregnancy, the relationship between different circulating Th cell subsets is not straightforward. Instead, these adaptations appear most evidently at the fetal–maternal interface, where for instance Tregs are enriched and promote fetal tolerance. Also innate immune cells, that is, natural killer cells and macrophages, are enriched, constituting the majority of decidual leukocytes. These cells not only contribute to immune regulation but also aid in establishing the placenta by promoting trophoblast recruitment and angiogenesis. Thus, proper interaction between leukocytes and placental trophoblasts is necessary for normal placentation and immune adaptation. Consequently, spontaneous maladaptation or interference of the immune system with toxic substances may be important contributing factors for the development of pregnancy complications such as preeclampsia, preterm labor, and recurrent miscarriages.