The dynamic profile and potential function of B-cell subsets during pregnancy

Uterine macrophages and NK cells exhibit population and gene-level changes after implantation but maintain pro-invasive properties

Introduction

Prior to pregnancy, hormonal changes lead to cellular adaptations in the endometrium allowing for embryo implantation. Critical for successful pregnancy establishment, innate immune cells constitute a significant proportion of uterine cells prior to arrival of the embryo and throughout the first trimester in humans and animal models. Abnormal uterine immune cell function during implantation is believed to play a role in multiple adverse pregnancy outcomes. Current work in humans has focused on uterine immune cells present after pregnancy establishment, and limited in vitro models exist to explore unique functions of these cells.

Methods

With single-cell RNA-sequencing (scRNAseq), we comprehensively compared the human uterine immune landscape of the endometrium during the window of implantation and the decidua during the first trimester of pregnancy.

Results

We uncovered global and cell-type-specific gene signatures for each timepoint. Immune cells in the endometrium prior to implantation expressed genes associated with immune metabolism, division, and activation. In contrast, we observed widespread interferon signaling during the first trimester of pregnancy. We also provide evidence of specific inflammatory pathways enriched in pre- and post-implantation macrophages and natural killer (NK) cells in the uterine lining. Using our novel implantation-on-a-chip (IOC) to model human implantation ex vivo, we demonstrate for the first time that uterine macrophages strongly promote invasion of extravillous trophoblasts (EVTs), a process essential for pregnancy establishment. Pre- and post-implantation uterine macrophages promoted EVT invasion to a similar degree as pre- and post-implantation NK cells on the IOC.

Conclusions

This work provides a foundation for further investigation of the individual roles of uterine immune cell subtypes present prior to embryo implantation and during early pregnancy, which will be critical for our understanding of pregnancy complications associated with abnormal trophoblast invasion and placentation.

B cell subsets contribute to myocardial protection by inducing neutrophil apoptosis after ischemia and reperfusion

A robust, sterile inflammation underlies myocardial ischemia and reperfusion injury (MIRI). Several subsets of B cells possess the immunoregulatory capacity that limits tissue damage, yet the role of B cells in MIRI remains elusive. Here, we sought to elucidate the contribution of B cells to MIRI by transient ligation of the left anterior descending coronary artery in B cell-depleted or -deficient mice. Following ischemia and reperfusion (I/R), regulatory B cells are rapidly recruited to the heart. B cell-depleted or -deficient mice exhibited exacerbated tissue damage, adverse cardiac remodeling, and an augmented inflammatory response after I/R. Rescue and chimeric experiments indicated that the cardioprotective effect of B cells was not solely dependent on IL-10. Coculture experiments demonstrated that B cells induced neutrophil apoptosis through contact-dependent interactions, subsequently promoting reparative macrophage polarization by facilitating the phagocytosis of neutrophils by macrophages. The in vivo cardioprotective effect of B cells was undetectable in the absence of neutrophils after I/R. Mechanistically, ligand-receptor imputation identified FCER2A as a potential mediator of interactions between B cells and neutrophils. Blocking FCER2A on B cells resulted in a reduction in the percentage of apoptotic neutrophils, contributing to the deterioration of cardiac remodeling. Our findings unveil a potential cardioprotective role of B cells in MIRI through mechanisms involving FCER2A, neutrophils, and macrophages.

Estrogen, the Peripheral Immune System and Major Depression – A Reproductive Lifespan Perspective

Major depression is a significant medical issue impacting millions of individuals worldwide. Identifying factors contributing to its manifestation has been a subject of intense investigation for decades and several targets have emerged including sex hormones and the immune system. Indeed, an extensive body of literature has demonstrated that sex hormones play a critical role in modulating brain function and impacting mental health, especially among female organisms. Emerging findings also indicate an inflammatory etiology of major depression, revealing new opportunities to supplement, or even supersede, currently available pharmacological interventions in some patient populations. Given the established sex differences in immunity and the profound impact of fluctuations of sex hormone levels on the immune system within the female, interrogating how the endocrine, nervous, and immune systems converge to impact women’s mental health is warranted. Here, we review the impacts of endogenous estrogens as well as exogenously administered estrogen-containing therapies on affect and immunity and discuss these observations in the context of distinct reproductive milestones across the female lifespan. A theoretical framework and important considerations for additional study in regards to mental health and major depression are provided.

Continuous activation of polymorphonuclear myeloid-derived suppressor cells during pregnancy is critical for fetal development

The maternal immune system is vital in maintaining immunotolerance to the semiallogeneic fetus for a successful pregnancy. Although studies have shown that myeloid-derived suppressor cells (MDSCs) play an important role in maintaining feto-maternal tolerance, little is known about the role of MDSCs in pregnancies with intrauterine growth retardation (IUGR). Here, we reported that the activation of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) during pregnancy was closely associated with fetal growth. In humans, class E scavenger receptor 1 (SR-E1), a distinct marker for human PMN-MDSCs, was used to investigate PMN-MDSC function during pregnancy. Continuous activation of SR-E1⁺ PMN-MDSCs was observed in all stages of pregnancy, accompanied by high cellular levels of ROS and arginase-1 activity, mediated through STAT6 signaling. However, SR-E1⁺ PMN-MDSCs in pregnancies with IUGR showed significantly lower suppressive activity, lower arginase-1 activity and ROS levels, and decreased STAT6 phosphorylation level, which were accompanied by an increase in inflammatory factors, compared with those in normal pregnancies. Moreover, the population of SR-E1⁺ PMN-MDSCs was negatively correlated with the adverse outcomes of newborns from pregnancies with IUGR. In mice, decreases in cell population, suppressive activity, target expression levels, and STAT6 phosphorylation levels were also observed in the pregnancies with IUGR compared with the normal pregnancies, which were rescued by the adoptive transfer of PMN-MDSCs from pregnant mice. Interestingly, the growth-promoting factors (GPFs) secreted by placental PMN-MDSCs in both humans and mice play a vital role in fetal development. These findings collectively support that PMN-MDSCs have another new role in pregnancy, which can improve adverse neonatal outcomes.