Pattern recognition at the maternal-fetal interface

Intrauterine infections represent a significant threat to fetal well-being and pregnancy outcome. Recent studies suggest that non-immune cells of the maternal-fetal interface can actively recognize and respond to microbes through pattern recognition receptors, in order to control pathogens that may compromise the pregnancy. However, these same innate immune responses may inadvertently lead to excessive inflammation or apoptosis at the maternal-fetal interface. Thus, pattern recognition receptors may play a key role in infection-related pregnancy complications. This review discusses what is currently known about the role of Toll-like receptors and NOD-like receptors in controlling infections at the maternal-fetal interface, and what impact their function may have on pregnancy.     

Immune interactions at the maternal-fetal interface: a focus on antigen presentation

Problem: Viruses and fetuses face similar immunologic challenges. Each must evade immune detection and destruction. The virus must avoid host recognition of intracellular infection; the fetus allogenic recognition. Each has manipulated the process of antigen presentation to allow survival in an immunologic environment otherwise predictably hostile. How have these approaches co‐evolved? What can they teach us about viral pathogenesis and immunologic interactions at the maternal‐fetal interface? Method of study: Review of relevant literature. Results: Special classical and non‐classical MHC class I products are spared from downregulation in the placenta and from viral immunoevasive strategies. Conclusions: Viruses rely upon some of the same strategies to avoid immune detection as do trophoblast cells. In the future, viral infections may prove a useful tool for studies of immunology at the maternal‐fetal interface.     

NKT cells at the maternal-fetal interface

Establishment of the maternal-fetal interface is characterized by the influx of maternal NK cells, macrophages, and T cells into the decidua. Although a great deal has been learned about the function of NK cells in the decidua, comparatively little is known of decidual T cell function. NKT cells are an unusual T cell subset capable of producing both Th1-like and Th2-like cytokines. Unlike conventional alphabeta T cells that recognize peptides in the context of MHC molecules, NKT cells recognize glycolipids presented by the MHC class I-like molecule, CD1d. Recent reports have demonstrated that NKT cells and CD1d are present at the maternal-fetal interface. Moreover, activation of NKT cells can have dramatic effects on pregnancy. In this article, we will review basic aspects of NKT cell biology and summarize the recent literature on NKT cells at the maternal-fetal interface.     

Immune modulation of HLA-G dimer in maternal-fetal interface

HLA-G is a non-classical human MHC class I molecule, which has several characteristics distinct from classical MHC, such as low polymorphism and restricted tissue distribution. HLA-G is expressed on placenta, thymus and some tumors. At the maternal-fetal interface, trophoblasts do not express major classical MHC class I molecules (MHCI), HLA-A and -B, to prevent normal T cell responses. Instead, HLA-G is expressed and can suppress a wide range of immune responses by binding to inhibitory immune cell surface receptors, such as leukocyte Ig-like receptor (LILR) B1 and LILRB2. HLA-G exists in various forms, including beta2m-associated or -free disulfide-linked dimers that can be expressed either at the cell surface or in soluble form. However, until recently the physiological role of these different molecular forms has been unclear. In this issue of the European Journal of Immunology, one article demonstrates that the disulfide-linked homodimer of beta2m-associated HLA-G is the major fraction expressed by trophoblast cells. The HLA-G dimer modulates the function of LILRB1-expressing antigen-presenting cells by principally binding to LILRB1. On the other hand, another recent report showed that beta2m-free disulfide-linked HLA-G dimers are produced by villous cytotrophoblast cells. Taken together, these results provide strong evidence in support of the hypothesis that HLA-G dimers play a role in immune suppression at the maternal-fetal interface. Further in-depth investigation will help to clarify the precise mechanism of HLA-G receptor recognition and signaling in vivo and the role of these interactions in successful reproduction. See accompanying article: (http://dx.doi.org/10.1002/eji.200737089).     

Dendritic cell function at the maternal-fetal interface

Understanding the evolutionary adaptation of the immune system to the developing fetus and placenta represents one of the most fascinating problems in reproductive biology. Recent work has focused on how the behavior of dendritic cells (DCs) is altered at the maternal-fetal interface to suit the unique requirements of pregnancy. This work has provided a significant new perspective into the long-standing immunological paradox of fetomaternal tolerance, and has opened up a new and intriguing area of research into the potential trophic role of uterine DCs in the peri-implantation period. Further research on the biology of uterine DCs promises to give insight into the pathogenesis of many clinically important disorders of pregnancy.     

The pro-inflammatory role of adiponectin at the maternal-fetal interface

Citation
McDonald EA, Wolfe MW. The pro‐inflammatory role of adiponectin at the maternal–fetal interface. Am J Reprod Immunol 2011; 66: 128–136 Problem A successful pregnancy is contingent on maternal tolerance of the immunologically foreign fetus. Prevalent diseases such as preeclampsia arise in part due to an inappropriate immune response by the placenta. A number of molecules have been proposed to temper cellular response to pro‐inflammatory mediators, including CD24 and Siglec10. Methods Cytotrophoblast cells from healthy term placentas were treated with adiponectin in vitro and analyzed with qPCR and ELISA‐based assays. Immunohistochemistry was performed on term villous sections and cultured trophoblasts. Results Treatment with adiponectin increased expression of IL‐1β and IL‐8. Term villi express CD24 in cytotrophoblasts and the syncytiotrophoblast, and Siglec10 by the syncytiotrophoblast. Treatment of trophoblast cells with adiponectin increased Siglec10 expression. Conclusion These data describe a role for adiponectin in enhancing pro‐inflammatory signals in in vitro syncytialized trophoblasts. Additionally, this represents the first time the CD24/Siglec10 pathway has been implicated in a trophoblast response to a pro‐inflammatory mediator.     

An insight into the dendritic cells at the maternal-fetal interface

The conditions that permit the genetically distinct fetus to survive and develop within the mother are among the most fascinating immunologic puzzles. The presence of dendritic cells in the maternal decidua pointed to a biologic role of antigen-presenting cells in maternal-fetal interaction. The method of study included recent findings on the lineage, maturity, phenotype and function of dendritic cells at the maternal-fetal interface. The increment of uterine dendritic cells occurs simultaneously with the decisive phase of gestation, when implantation takes place. Decidual dendritic cells of the first trimester pregnancy, with a phenotype characteristic of the mature myeloid lineage, express MHC class II, co-stimulatory and adhesion molecules, control Th1/Th2 balance and activate the proliferative response of autologous NK cells. Dendritic cells are specifically equipped to control immunity, to trigger immune response and also to maintain tolerance, avoiding the rejection of the conceptus by the maternal immune system.     

NK cell tolerance and the maternal-fetal interface.

Natural killer (NK) cells play a fundamental role in the innate immune response through their ability to secrete cytokines and kill target cells without prior sensitization. These effector functions are central to NK cell anti-viral and anti-tumor abilities. Due to their cytotoxic nature, it is vital that NK cells have the capacity to recognize normal self-tissue and thus prevent their destruction. In addition to their role in host defense, NK cells accumulate at the maternal-fetal interface and are thought to play a critical role during pregnancy. The close proximity of uterine NK (uNK) cells to fetal trophoblast cells of the placenta would seemingly lead to catastrophic consequences, as the trophoblast cells are semi-allogeneic. A fundamental enigma of pregnancy is that the fetal cells constitute an allograft but, in normal pregnancies, they are in effect not perceived as foreign and are not rejected by the maternal immune system. Although the mechanisms involved in achieving NK cell tolerance are becoming increasingly well-defined, further clarification is required, given the clinical implications of this work in the areas of infection, transplantation, cancer and pregnancy. Herein, we discuss several mechanisms of NK cell tolerance and speculate as to how they may apply to uNK cells at the maternal-fetal interface.     

Perforin and Fas/FasL cytolytic pathways at the maternal-fetal interface

The immunogenetic enigma of maternal acceptance of the fetal semiallograft has been termed an immunological paradox. The first trimester decidua is heavily infiltrated with CD56(bright) CD16- uterine natural killer (uNK) cells which must be prepared to respond to potential pathogen challenges and still be able to control immune responses that allow the development of the fetus. The significant presence of cytolytic mediators, perforin and Fas/Fas ligand (FasL), at the maternal-fetal interface raises a question of their role(s) in the immunological interrelations between maternal tissues and trophoblast cells. As uNK cells in vitro lyse target cell lines (K562, P815 and P815Fas) using these effector molecules, it seems that, although immunocompetent, their cytotoxicity is not directed against trophoblast during normal pregnancy. Therefore, it is generally believed that the hormonal and Th1/Th2 cytokine balance plays an important role in the tolerance and maintenance of pregnancy. This paper gives an overview of the recent findings on the complex immunological events that occur at the maternal-fetal interface.     

HLA-G in reproduction: studies on the maternal-fetal interface

For more than a decade, investigators have known that membrane-bound and soluble isoforms of the HLA class Ib molecule, HLA-G, are present at the maternal-fetal interface. Although it is clear that extravillous cytotrophoblast cells are major producers, other cells may also contribute. Recent studies in our laboratory raised the question of whether soluble isoforms might reach the maternal and/or fetal blood circulation. A capture enzyme-linked immunoabsorbent assay (ELISA) identified soluble HLA-G (sHLA-G) in maternal blood throughout pregnancy but failed to detect sHLA-G in cord sera. Further studies suggested that the circulating proteins may be either free heavy chain (sHLA-G1 and/or sHLA-G2) or exclusively sHLA-G2. To study the potential function(s) of the soluble isoforms to modulate local or systemic immunity in mothers, we generated recombinant sHLA-G1 and -G2 in both prokaryotic and eukaryotic systems. Preliminary experiments conducted using DNA microarray analysis suggest that sHLA-G is capable of modulating gene expression in blood mononuclear leukocytes. Potential local targets were also identified; decidual and placental macrophages but not trophoblast cells contained mRNA encoding two of the known receptors for HLA-G, ILT2 and ILT4. Collectively, the studies are consistent with the hypothesis that sHLA-G produced at the maternal-fetal interface targets to the cells of the monocyte/macrophage lineage and modulates their functions for the benefit of pregnancy.     

The presence of functional mannose receptor on macrophages at the maternal-fetal interface

BACKGROUND: The mannose receptor (MR) is involved in the initiation of the immune response and regulation of homeostasis during inflammation and tissue remodeling. METHODS: Distribution, endocytosis and possible natural ligand tumor associated glycoprotein-72 (TAG-72) for the MR have been examined by immunohistology, immunocytochemistry and flow cytometry at the maternal-fetal interface, characterized by extensive tissue remodeling. RESULTS: Contrary to disseminated distribution of the MR positive (MR+) cells in term placenta, the MR+ cells of early pregnancy decidua intimately surrounded glands and followed tissue distribution of CD14 positive cells. The mannose receptor was present on freshly isolated first trimester decidual mononuclear cells and distributed mostly on macrophages (77.08 +/- 10.55%, mean +/- SD). The expression of the MR on CD14 positive cells decreased following 18 h culture (P < 0.01) and was accompanied by the reduction of fluorescein isothiocyanate (FITC)-dextran uptake. PAM-1 anti-MR antibody, mannan and TAG-72 reduced FITC-dextran uptake by decidual macrophages. CONCLUSIONS: These data indicate that the MR+ macrophages, surrounding early decidual glands, are able to internalize ligands for carbohydrate recognition domain of the receptor, including decidual secretory phase mucin TAG-72.     

Integrins and extracellular matrix proteins at the maternal-fetal interface in domestic animals

Establishment of pregnancy in mammals requires coordinated conceptus-maternal interactions involving numerous hormones, growth factors and cytokines acting via specific receptors in the uterus. Uterine secretions play an important role in establishing synchrony between development of the conceptus and uterine receptivity, as well as in conceptus remodeling, adhesion, implantation and placentation in domestic species. Studies of non-invasive implantation in domestic livestock provide valuable opportunities to investigate fundamental processes of the initial events of apposition, attachment and adhesive interactions that are shared among species. In pigs and sheep, it appears that integrins play a dominant role in these fundamental processes via interactions with extracellular matrix molecules and other ligands to transduce cellular signals in uterine epithelial cells and conceptus trophectoderm. This review considers several of the potential integrin-binding ligands involved in the complex implantation adhesion cascade in pigs and sheep along with in vitro evidence for the transduction of cytoplasmic signals that may be required to sustain fetal and maternal contributions to the formation of the epitheliochorial placenta.     

Interleukin-11 signaling is required for the differentiation of natural killer cells at the maternal-fetal interface.

Interleukin-11 (IL-11) is a multifunctional hematopoietic growth factor that has been implicated in the control of reproduction. Studies on IL-11 receptor-alpha (IL-11R alpha)-deficient mice showed that female mice are infertile due to defective decidualization. In this report, we evaluated the development of decidual cells, immune cells, and the vasculature associated with the implantation site of IL-11R alpha-deficient mice; with the aim of better understanding the nature of the fertility defect. Messenger RNAs for decidual differentiation, such as decidual prolactin-related protein and prolactin-like protein-J are expressed in the IL-11R alpha mutant. However, the number of decidual cells expressing these genes is decreased in the mutant compared with the wild-type control. Although, trophoblast cells differentiate and express placental lactogen-I in the IL-11R alpha-deficient uterine environment, they fail to progress and expand in number. Defects in the organization of the decidual vasculature were also apparent in the IL-11R alpha mutant uterus. The most dramatic effect of IL-11 signaling was on the hematopoietic environment of the uterine decidua. Differentiated/perforin-expressing uterine natural killer (NK) cells were virtually absent from implantation sites of IL-11R alpha mutant mice. NK cell precursors were capable of homing to the IL-11R alpha-deficient uterus and a known regulator of NK cell differentiation; IL-15 was expressed in the IL-11R alpha mutant uterus. Splenic NK cells from IL-11R alpha mutant mice were also able to respond to IL-15 in vitro. Thus, the defect in NK precursor cell maturation was not intrinsic to the NK precursor cells but was dependent upon the tissue environment. In summary, IL-11 signaling is required for decidual-specific maturation of NK cells.     

The immunolocalization of bcl-2 at the maternal-fetal interface in healthy and failing pregnancies

Programmed cell death by apoptosis occurs in both fetal and maternal tissues during early pregnancy. To investigate a role for apoptosis at the maternal-fetal interface, we have immunolocalized the bcl-2 protein in formalin-fixed decidual and placental tissue collected from women undergoing surgical termination of pregnancy (n = 22), from women undergoing a sporadic miscarriage (n = 16) and from women with a history of recurrent pregnancy loss (more than three consecutive pregnancy losses; n = 22) undergoing a further miscarriage. In all three groups, bcl-2+ cells were found in aggregates and dispersed in the stroma, and immunoreactivity was observed in glandular epithelium. Double immunostaining revealed that a majority of stromal bcl-2+ cells were CD56+ large granular lymphocytes. A computerized image analysis revealed no significant differences in percentage area of bcl-2 or CD56+ immunostaining. Significantly more biopsies from the surgical termination group (4/10) had > 20% positive immunostaining for CD56 compared with 0% in the other two groups combined (0/20; P < 0.05). Bcl- 2 immunoreactivity was observed in the villi syncytiotrophoblast, and staining intensity was consistently greater in the surgical termination group. The possible roles of bcl-2 at the maternal-fetal interface are discussed.      

The skewed TCR-BV repertoire displayed at the maternal-fetal interface of women with unexplained pregnancy loss

PROBLEM: The study was undertaken to investigate T-cell receptor (TCR) variable beta (BV)-chain usage at maternal-fetal interface and explore the relationship between the skewed TCR-BV usage and unexplained pregnancy losses. METHOD OF STUDY: A total of 57 patients with unexplained pregnancy loss including 39 cases with unexplained spontaneous abortion and 18 cases with unexplained recurrent spontaneous abortion (RSA) were chosen in Renji Hospital, Shanghai Second Medical University matched with 41 women with normal pregnancies in first trimester between September 2002 and November 2003. A high-resolution spectratyping analysis of complementarity-determining region 3 (CDR3) was used to detect and compare the degree and pattern of TCR-BV repertoire usage at the maternal-fetal interface between patients with pregnancy loss and normal controls. RESULTS: There were two comparisons of TCR usage performed between patients and controls, which included the degree (mean value of every TCR-BVn expression) and the pattern (skewed TCR-BVn frequency). The skewed TCR-BVn is defined as an absolute BVn usage of > 5% calculated from the formula or a double increased BVn usage compared with the mean value of normal BVn. According to the degree of TCR-BV usage, BV2 (P = 0.046), BV10 (P = 0.016), and BV11 (P = 0.030) in spontaneous abortion group and BV19 (P = 0.038) in RSA group showed higher usage, while BV5.2 (P = 0.006 and P = 0.046) in both abortion groups showed significantly lower usage when compared with normal controls. About the pattern of skewed TCR-BV distribution, we found that TCR-BV2, -3, -6, and -7 were the four most common BV families in deciduas of patients with both types of abortion and normal controls. Women with spontaneous abortion demonstrated higher frequency of BV10 (P = 0.035) and lower frequencies of BV4 (P = 0.002) and BV5.2 (P = 0.003) in comparison with controls. In RSA, higher frequencies of BV15 (P = 0.018), BV19 (P = 0.049), and BV20 (P = 0.018), in the mean time, lower frequencies of BV4 (P = 0.026) and BV7 (P = 0.018) distributions were verified. CONCLUSIONS: Our results suggested that a significant skewed TCR-BV repertoire occurred at the maternal-fetal interface with patients undergoing abortion. The specific skewed usages of TCR-BV might be associated with the susceptibility to unexplained pregnancy loss.     

IL-18 is present at the maternal-fetal interface and enhances cytotoxic activity of decidual lymphocytes

PROBLEM: Perforin expressing uterine natural killer (uNK) cells are under complex cytokine influence. The aim of the study was to investigate the presence and role of interleukin (IL)-18 on NK cytolytic potential at maternal-fetal (M-F) interface. METHOD OF STUDY: Peripheral blood cells and decidual tissue were obtained from elective pregnancy termination of normal human 6-10-week-old pregnancies. Perforin expression and cytolytic activity of peripheral blood (PBL) and decidual lymphocytes (DL) were analyzed by flow cytometry. IL-18 positive decidual adherent cells (DAC) were detected by the same method. Interleukin-18 and IL-18 receptor (IL-18R) expression on the trophoblastic cells was detected by immunohistology using biotinylated anti-IL-18 and IL-18R monoclonal antibodies. RESULTS: The IL-18 added in a dose of 10 ng/mL up-regulates perforin expression and cytolytic activity of DL. Simultaneous stimulation with IL-18 and IL-12 enhanced DL cytolytic activity, while IL-18 combined with IL-10 or IL-15 did not show this effect. Cytolytic activity of PBL was up-regulated by IL-18 as well, and this effect was enhanced by the addition of IL-12 and IL-15. Interleukin-18 did not affect perforin-protein expression in cultured PBL. Approximately 20% of DAC were IL-18 positive and these cells were mostly human leukocyte antigen (HLA)-DR negative. IL-18R positive cells were found on syncytiotrophoblast cell layer, interstitial tissue cells of villi and fetal blood cells. There was no detectable IL-18 staining on trophoblast cell layer on villi, but strong staining of fetal blood cells in villous vessels. CONCLUSION: These are first results showing IL-18R expression, but not IL-18 expression on villous trophoblastic cells, as well as enhancement of perforin expression and NK cytolytic potential of DL under the influence of IL-18. IL-18 in concert with other cytokines and hormones could play an important role in the regulation of cytolytic potential of first trimester pregnancy decidual and peripheral blood NK cells.     

早期自然流产患者母胎界面E-钙黏素与β-连环素的异常表达

目的探讨早期自然流产患者绒毛和蜕膜组织E-钙黏素（E—cadherin）与β-连环素（β-catenin）的异常表达。方法采用免疫组化sP法和显微图像分析系统，检测20例早期自然流产（自然流产组）及24例正常早期人工流产（正常妊娠组）绒毛和蜕膜组织内E—cadherin、β-catenin表达的平均光度及积分光度。结果E—cadherin、β-catenin．在自然流产组和正常妊娠组绒毛与蜕膜组织中均有表达。自然流产组绒毛细胞滋养细胞和蜕膜细胞表面E—cadherin、β-catenin表达平均光度及积分光度均明显高于正常妊娠组，P〈0．001，差异有统计学意义。结论E—cadherin及β-catenin对妊娠维持起一定的作用。蜕膜及绒毛组织E—cadherin与β-catenin的高表达可能是导致早期自然流产的原因之一。