Myeloid cell alterations in the mouse placenta precede the onset of labor and delivery

LILRB4 regulates the function of decidual MDSCs via the SHP-2/STAT6 pathway during Toxoplasma gondii infection

BACKGROUND

Toxoplasma gondii infection can cause adverse pregnancy outcomes, such as recurrent abortion, fetal growth restriction and infants with malformations, among others. Decidual myeloid-derived suppressor cells (dMDSCs) are a novel immunosuppressive cell type at the fetal-maternal interface which play an important role in sustaining normal pregnancy that is related to their high expression of the inhibitory molecule leukocyte immunoglobulin-like receptor B4 (LILRB4). It has been reported that the expression of LILRB4 is downregulated on decidual macrophages after T. gondii infection, but it remains unknown whether T. gondii infection can induce dMDSC dysfunction resulting from the change in LILRB4 expression.

METHODS

LILRB4-deficient (LILRB4^-/-) pregnant mice infected with T. gondii with associated adverse pregnancy outcomes, and anti-LILRB4 neutralized antibodies-treated infected human dMDSCs were used in vivo and in vitro experiments, respectively. The aim was to investigate the effect of LILRB4 expression on dMDSC dysfunction induced by T. gondii infection.

RESULTS

Toxoplasma gondii infection was observed to reduce STAT3 phosphorylation, resulting in decreased LILRB4 expression on dMDSCs. The levels of the main functional molecules (arginase-1 [Arg-1], interleukin-10 [IL-10]) and main signaling molecules (phosphorylated Src-homology 2 domain-containing protein tyrosine phosphatase [p-SHP2], phosphorylated signal transducer and activator of transcription 6 [p-STAT6]) in dMDSCs were all significantly reduced in human and mouse dMDSCs due to the decrease of LILRB4 expression induced by T. gondii infection. SHP-2 was found to directly bind to STAT6 and STAT6 to bind to the promoter of the Arg-1 and IL-10 genes during T. gondii infection.

CONCLUSIONS

The downregulation of LILRB4 expression on dMDSCs induced by T. gondii infection could regulate the expression of Arg-1 and IL-10 via the SHP-2/STAT6 pathway, resulting in the dysfunction of dMDSCs, which might contribute to adverse outcomes during pregnancy by T. gondii infection.

Single cell profiling at the maternal-fetal interface reveals a deficiency of PD-L1+ non-immune cells in human spontaneous preterm labor

The mechanisms that underlie the timing of labor in humans are largely unknown. In most pregnancies, labor is initiated at term (≥ 37 weeks gestation), but in a signifiicant number of women spontaneous labor occurs preterm and is associated with increased perinatal mortality and morbidity. The objective of this study was to characterize the cells at the maternal-fetal interface (MFI) in term and preterm pregnancies in both the laboring and non-laboring state in Black women, who have among the highest preterm birth rates in the U.S. Using mass cytometry to obtain high-dimensional single-cell resolution, we identified 31 cell populations at the MFI, including 25 immune cell types and six non-immune cell types. Among the immune cells, maternal PD1⁺ CD8 T cell subsets were less abundant in term laboring compared to term non-laboring women. Among the non-immune cells, PD-L1⁺ maternal (stromal) and fetal (extravillous trophoblast) cells were less abundant in preterm laboring compared to term laboring women. Consistent with these observations, the expression of CD274, the gene encoding PD-L1, was significantly depressed and less responsive to fetal signaling molecules in cultured mesenchymal stromal cells from the decidua of preterm compared to term women. Overall, these results suggest that the PD1/PD-L1 pathway at the MFI may perturb the delicate balance between immune tolerance and rejection and contribute to the onset of spontaneous preterm labor.

Myeloid-derived suppressor cells in obstetrical and gynecological diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of myeloid-origin cells which have immunosuppressive activities in several conditions, such as cancer and inflammation. Recent research has also associated MDSCs with numerous obstetrical and gynecological diseases. During pregnancy, MDSCs accumulate to ensure maternal-fetal immune tolerance, whereas they are decreased in patients who suffer from early miscarriage or pre-eclampsia. While the etiology of endometriosis is still unknown, abnormal accumulation of MDSCs in the peripheral blood and peritoneal fluid, alongside an increased level of reactive oxygen species (ROS), has been observed in these patients, which is central to the cellular immune regulations by MDSCs. Additionally, the regulation of MDSCs observed in tumours is also applicable to gynecologic neoplasms, including ovarian cancer and cervical cancer. More recently, emerging evidence has shown that there are high levels of MDSCs in premature ovarian failure (POF) and in vitro fertilization (IVF), but the underlying mechanisms are unknown. In this review, the generation and mechanisms of MDSCs are summarized. In particular, the modulation of these cells in immune-related obstetrical and gynecological diseases is discussed, including potential treatment options targeting MDSCs.

Myeloid-derived suppressor cells depletion may cause pregnancy loss via upregulating the cytotoxicity of decidual natural killer cells

PROBLEM

Maternal immune system tolerance to the semiallogeneic fetus is critical for a successful pregnancy. Studies have shown that myeloid-derived suppressor cells (MDSCs) play an important role in maintaining feto-maternal tolerance. However, the mechanisms remain poorly understood.

METHODS

Flow cytometry was used to evaluate the percentage of MDSCs in an allogeneic-normal-pregnant mouse model during different periods of gestation. We further assessed the percentage of MDSCs and their subtypes (granulocytic MDSCs [GR-MDSCs] and monocytic MDSCs [MO-MDSCs]) in a spontaneous abortion mouse model. The levels of the immunosuppressive molecules ARG-1, iNOS, IL-10, and TGF-β in MDSCs were also evaluated. MDSCs were depleted by anti-Gr-1 injection, and the resorption rate was calculated. The cytotoxicity of decidual natural killer (NK) cells was evaluated, and the percentage of regulatory NK (NKreg) cells and regulatory T lymphocytes (Tregs) were evaluated.

RESULTS

Myeloid-derived suppressor cells was accumulated in a time-dependent manner during pregnancy. However, the percentage of MDSCs was decreased in the spontaneous abortion mice compared with that in the control mice. In addition, the levels of ARG-1, iNOS, IL-10, and TGF-β in MDSCs decreased differentially. Finally, depletion of MDSCs was associated with increased rates of resorption and the proportion of NKreg and Treg cells in uterine tissues; meanwhile, the cytotoxicity of decidual NK cells was upregulated by increasing the level of perforin, granzyme B, and natural killer group protein 2 D-activating NK receptor (NKG2D).

CONCLUSION

Depletion of MDSCs may cause pregnancy loss, while upregulating the cytotoxicity of decidual NK cells and increasing NKreg and Treg cell numbers.

Decidual-Placental Immune Landscape During Syngeneic Murine Pregnancy

Adaptive immune system, principally governed by the T cells-dendritic cells (DCs) nexus, is an essential mediator of gestational fetal tolerance and protection against infection. However, the exact composition and dynamics of DCs and T cell subsets in gestational tissues are not well understood. These are controlled in human physiology by a complex interplay of alloantigen distribution and presentation, cellular/humoral active and passive tolerance, hormones/chemokines/angiogenic factors and their gradients, systemic and local microbial communities. Reductive discrimination of these factors in physiology and pathology of model systems and humans requires simplification of the model and increased resolution of interrogative technologies. As a baseline, we have studied the gestational tissue dynamics in the syngeneic C57BL/6 mice, as the simplest immunological environment, and focused on validating the approach to increased data density and computational analysis pipeline afforded by highly polychromatic flow cytometry and machine learning interpretation. We mapped DC and T cell subsets, and comprehensively examined their maternal (decidual)-fetal (placental) interface dynamics. Both frequency and composition of decidual DCs changed across gestation, with a dramatic increase in myeloid DCs in early pregnancy, and exclusion of plasmacytoid DCs. CD4+ T cells, in contrast, were lower at all gestational ages and an unusual CD4-CD8-TCRαβ+group was prominent at mid-pregnancy. Dimensionality reduction with machine learning-aided clustering revealed that CD4-CD8- T cells were phenotypically different from CD4+ and CD8+ T cells. Additionally, divergence between maternal decidual and fetal placental compartment was prominent, with absence of DCs from the placenta, but not decidua or embryo. These results provide a novel framework and a syngeneic baseline on which the specific role of alloantigen/tolerance, polymicrobial environment, and models of pregnancy pathology can be precisely modeled and analyzed.

Placental immune state shifts with gestational age

PROBLEM

Placental immunologic functions are implicated in both the maintenance of a healthy pregnancy and the pathogenesis of obstetric complications. Immune populations at the maternal-fetal interface are hypothesized to support fetomaternal tolerance, defend the fetus from infection, and contribute to labor initiation. Despite the many potential roles of placental immune cells in normal and abnormal pregnancy, little is known about placental immune population dynamics over gestation, particularly near parturition.

METHOD OF STUDY

A daily placental immune cell census was established in a murine model by flow cytometry from mid to late gestation and compared to the maternal systemic immune census. Shifts in the placental immune state were further characterized through cytokine ELISAs.

RESULTS

The placental immune census is distinct from the maternal systemic immune census, although the cells are primarily maternal in origin. Near term parturition, the placenta contains fewer CD11c-positive myeloid cells and regulatory T cells, and there is a concurrent decrease in placental IL-9 and IL-35.

CONCLUSION

The immune profile of the placenta demonstrates a decrease in both regulatory immune cell types and cytokines late in gestation. Establishing the placental immune population dynamics over a healthy pregnancy will allow future investigation of placental immune cells during abnormal pregnancy.

Immune regulatory network in successful pregnancy and reproductive failures

Maternal immune system must tolerate semiallogenic fetus to establish and maintain a successful pregnancy. Despite the existence of several strategies of trophoblast to avoid recognition by maternal leukocytes, maternal immune system may react against paternal alloantigenes. Leukocytes are important components in decidua. Not only T helper (Th)1/Th2 balance, but also regulatory T (Treg) cells play an important role in pregnancy. Although the frequency of Tregs is elevated during normal pregnancies, their frequency and function are reduced in reproductive defects such as recurrent miscarriage and preeclampsia. Tregs are not the sole population of suppressive cells in the decidua. It has recently been shown that regulatory B10 (Breg) cells participate in pregnancy through secretion of IL-10 cytokine. Myeloid derived suppressor cells (MDSCs) are immature developing precursors of innate myeloid cells that are increased in pregnant women, implying their possible function in pregnancy. Natural killer T (NKT) cells are also detected in mouse and human decidua. They can also affect the fetomaternal tolerance. In this review, we will discuss on the role of different immune regulatory cells including Treg, γd T cell, Breg, MDSC, and NKT cells in pregnancy outcome.

CD33(+) /HLA-DR(neg) and CD33(+) /HLA-DR(+/-) Cells: Rare Populations in the Human Decidua with Characteristics of MDSC

PROBLEM

Human pregnancy needs a remarkable local immune tolerance toward the conceptus. Myeloid-derived suppressor cells (MDSC) are important players promoting cancer initiation and progression by suppressing T-cell functions and thus inducing immune tolerance. Therefore, MDSC were expected within decidua.

METHODS

Subpopulations of CD33(+) immune cells were isolated from human early pregnancy decidua and characterized phenotypically and functionally by microscopy, FACS analysis, RT-PCR, Western blotting and in the coculture with T cells.

RESULTS

Decidua harbors CD33(+) /HLA-DR(neg) and CD33(+) /HLA-DR(+/-) cells which both express arginase, iNOS and IDO and a typical cytokine profile. Both subtypes potently suppress T-cell proliferation and therefore fulfill the criteria of MDSC.

CONCLUSION

We characterized a new population of CD33(+) /HLA-DR(neg) and CD33(+) /HLA-DR(+/-) cells in human early pregnancy decidua with properties of classical MDSC and thus potentially being an important player in immune tolerance in pregnancy.

Reduced Myeloid-derived Suppressor Cells in the Blood and Endometrium is Associated with Early Miscarriage

PROBLEM

The contribution of myeloid-derived suppressor cells (MDSC) in patients suffering from early or recurrent miscarriage is unknown. MDSC are implicated in modulation of T-cell response in healthy pregnancies; however, the role of MDSC in patients suffering from miscarriage has not been studied. We hypothesized that MDSC play major role in inducing maternal-fetal tolerance and this tolerance is compromised in patients suffering from miscarriage.

METHOD OF STUDY

MDSC level was assessed by flow cytometry and immunostaining in blood and endometrial decidua, respectively. Activation of T cells was determined by MTT proliferation and IL-2 ELISA assays.

RESULTS AND CONCLUSION

The miscarriage patients harbor reduced level of functionally suppressive MDSC in blood and endometrium as compared to healthy control women with successful pregnancies. These results suggest MDSC regulate maternal tolerance in healthy pregnancies and that drug inducing MDSC could have therapeutic implication in the miscarriage patients.

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.