Maternal Decidual Macrophages Inhibit NK Cell Killing of Invasive Cytotrophoblasts During Human Pregnancy
Human pregnancy is an immunological paradox. Semi-allogeneic (fetal) placental cells (extravillous cytotrophoblasts; CTBs) invade the uterine lining (decidua), which contains a unique decidual Natural Killer (dNK) cell population, identified by the cell-surface phenotype CD56(bright)CD16(-)CD3(-) and CD14(+) CD206(+) macrophages (dMac). Previous reports suggested that human dNK cells are not a threat to the feto-placental unit because they are anergic. In contrast, here we showed that purified and exogenously stimulated dNK cells are capable killers of cellular targets, including semi-allogeneic CTBs. However, dMacs in the decidual leukocyte (DL) population restrained dNK killing through a Transforming Growth Factor (TGF)-β1-dependent mechanism. Our findings support a new model whereby dNK cells, capable of killing CTBs, are prevented from doing so by neighboring macrophages, thus protecting the fetal cells from NK cell attack. We speculate that this mechanism would inhibit dNK cell-mediated killing, even in conditions where high levels of cytokines may stimulate dNK cells, which could pose a threat to the developing placenta.
Available from: B. Anne Croy
- "Only a small proportion of freshly isolated CD56 + uNK express the degranulation marker CD107 (also known as lysosomal-associated membrane protein 1; LAMP1), the most abundant membrane glycoprotein of lytic granules, in response to HLA-I negative 721.122 cells (Apps et al. 2011b). The low level expression of CD107 by uNK cells may be a strategic plan adopted from pNK to minimize degranulation-associated apoptosis (Cohnen et al. 2013). In a redirected killing assay using mouse mastocytoma P815 cells, the engagement of NKp46 greatly improved the degranulation and cytotoxic capacity of human uNK cells (El Costa et al. 2008). "
[Show abstract] [Hide abstract]
ABSTRACT: The maternal-fetal interface undergoes dynamic changes that promote successful development of the embryo/fetal allograft during pregnancy. This immune privilege of the conceptus is mediated through local and systemic cellular responses. In species in which endometrial decidualization accompanies pregnancy, unique immune cell niches are found. Many studies have addressed the enigmatic roles of uterine (u)NK cells as killers and helpers because they are frequently found in the uterine lining and decidua of normal and pathological pregnancies. Accumulating evidence indicates that uNK cells are induced and transformed by sensing signals within their microenvironment to both protect the mother from the fetal allograft and support the fetus during its development. Here, we review the mechanisms that modulate these functions of uNK cells during pregnancy. We suggest that uNK cells must be tightly regulated in order to serve these two roles and support a healthy pregnancy.
Available from: Carrie Shawber
- "Embryo implantation and trophoblast invasion create a pro-inflammatory environment leading to the recruitment of immune cells that mediate maternal tolerance to the semi-allogeneic embryo [5,10]. Decidual macrophages are the second most abundant immune cell population at the implantation site, comprising 20-30% of immune cells in the uterine decidua [4,11,12]. "
[Show abstract] [Hide abstract]
Angiogenesis and macrophage recruitment to the uterus are key features of uterine decidualization; the progesterone-mediated uterine changes that allow for embryo implantation and initiation of pregnancy. In the current study, we characterized the expression of vascular endothelial growth factor receptor-1 (VEGFR-1) in macrophages and endothelial cells of the peri-implantation uterus and determined if VEGFR-1 function is required for decidual angiogenesis, macrophage recruitment, and/or the establishment of pregnancy.
Expression of VEGFR-1 in uterine endothelial cells and macrophages was determined with immunohistochemistry. To assess the effect of continuous VEGFR-1 blockade, adult female mice were given VEGFR-1 blocking antibody, MF-1, every 3 days for 18 days. After 6 doses, females were mated and a final dose of MF-1 was given on embryonic day 3.5. Endothelial cells and macrophages were quantified on embryonic day 7.5. Pregnancy was analyzed on embryonic days 7.5 and 10.5.
F4/80+ macrophages are observed throughout the stroma and are abundant adjacent to the endometrial lumen and glands prior to embryo implantation and scatter throughout the decidua post implantation. VEGFR-1 expression is restricted to the uterine endothelial cells. F4/80+ macrophages were often found adjacent to VEGFR-1+ endothelial cells in the primary decidual zone. Continuous VEGFR-1 blockade correlates with a significant reduction in decidual vascular and macrophage density, but does not affect embryo implantation or maintenance of pregnancy up to embryonic day 10.5.
We found that VEGFR-1 functions in both decidual angiogenesis and macrophage recruitment to the implantation site during pregnancy. VEGFR-1 is expressed by endothelial cells, however blocking VEGFR-1 function in endothelial cells results in reduced macrophage recruitment to the uterus. VEGFR-1 blockade did not compromise the establishment and/or maintenance of pregnancy.
Available from: intjdevbiol.com
[Show abstract] [Hide abstract]
ABSTRACT: Survival of the allogeneic embryo in the uterus depends on the maintenance of immune tolerance at the maternal-fetal interface. The pregnant uterus is replete with activated maternal immune cells. How this immune tolerance is acquired and maintained has been a topic of intense investigation. The key immune cells that predominantly populate the pregnant uterus are natural killer (NK) cells. In normal pregnancy, these cells are not killers, but rather provide a microenvironment that is pregnancy compatible and supports healthy placentation. In placental mammals, an array of highly orchestrated immune elements to support successful pregnancy outcome has been incorporated. This includes active cooperation between maternal immune cells, particularly NK cells, and trophoblast cells. This intricate process is required for placentation, immune regulation and to remodel the blood supply to the fetus. During the past decade, various types of maternal immune cells have been thought to be involved in cross-talk with trophoblasts and in programming immune tolerance. Regulatory T cells (Tregs) have attracted a great deal of attention in promoting implantation and immune tolerance beyond implantation. However, what has not been fully addressed is how this immune-trophoblast axis breaks down during adverse pregnancy outcomes, particularly early pregnancy loss, and in response to unscheduled inflammation. Intense research efforts have begun to shed light on the roles of NK cells and Tregs in early pregnancy loss, although much remains to be unraveled in order to fully characterize the mechanisms underlying their detrimental activity. An increased understanding of host-environment interactions that lead to the cytotoxic phenotype of these otherwise pregnancy compatible maternal immune cells is important for prediction, prevention and treatment of pregnancy maladies, particularly recurrent pregnancy loss. In this review, we discuss relevant information from experimental and human models that may explain the pregnancy disrupting roles of these pivotal sentinel cells at the maternal-fetal interface.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.