Antigen presenting cells and HLA-G – a review

Assessment of immune cells in the uterine fluid at the time of the embryo transfer

PROBLEM

Although endometrial receptivity is a key factor in influencing implantation in both naturally conceived and assisted reproductive technology (ART) cycles, very little is known about the endometrium milieu around the time of implantation. Previous studies have demonstrated the presence of several cytokines in the endometrium that affect implantation. However, there is lacking data about the presence of immune cell subtypes within the endometrium and in the uterine cavity at the time of implantation.

METHOD OF STUDY

This study was approved by the Institutional Review Board (# 225589). The study was designed as a prospective observational cohort study between May 2021 and December 2022 at a single academic-based fertility center. All patients underwent at least one In Vitro Fertilization (IVF) cycle and have frozen embryos. Twenty-four participants were recruited for this study which was conducted during the frozen embryo transfer (FET) cycle regardless of the outcome of previous cycles. Two samples were acquired from each subject, denoted as lower and upper. A trial transfer catheter was introduced under ultrasound guidance into the lower uterine segment. Upon removal, the tip was rinsed in IMDM medium containing 10% FBS (lower uterus). A transfer catheter was then loaded with the embryo that was placed in the upper uterus under ultrasound guidance. The tip of the transfer catheter was rinsed in separate aliquot of the above media (upper uterus). After centrifugation, pelleted cells were stained for the following surface markers: CD45, CD3, CD19, CD4, CD8, gamma delta TCR, CD25, CD127, CD66b, CD14, CD16, CD56 and acquired on Sony SP6800 Spectral Analyzer.

RESULTS

Upon staining the pelleted cells, we were able to identify viable leukocytes from samples obtained from both, upper and lower uterus (0.125 × 106 cells ± SD 0.32), (0.123 × 106 cells ± SD 0.12), respectively. Among total viable cells, there was no significant difference in both percent and number of CD45+ cells between the upper and lower uterus (9.88% ± 6.98 SD, 13.67% ± 9.79 SD, p = .198) respectively. However, there was significantly higher expression of CD3+ (p = .006), CD19+ (p = .032) and CD14+ (p = .019) cells in samples collected from upper compared to lower uterus. Within all CD3+ cells, we found that gamma delta T cells (GDT) were the major population of T cells in both upper and lower uterus. In contrast, CD8+ T cells were significantly higher in the lower uterus when compared to the upper uterus (p = .009). There was no statistically significant difference in the expression of CD4+ T cells, T regulatory cells (CD4+CD25+CD127-), NK cells (CD56+), neutrophils (CD66b+) and FcγRIII+ cells (CD16+) between upper and lower uterus.

CONCLUSIONS

We believe the immune milieu at the time of embryo transfer will affect implantation. Understanding the composition of immune cells will guide further research in identifying optimal immune milieus that favor implantation. Comprehensive analysis of endometrium is expected to lead to new diagnostic and therapeutic approaches to improve IVF outcomes.

Relative expression of receptors in uterine natural killer cells compared to peripheral blood natural killer cells

One would expect maternal immune cells to attack the invading trophoblast as the placenta is semi-allogenic. However, they appear to cooperate with the trophoblast in disrupting the arterial wall which has been determined in several studies. uNK cells are a particular type of immune cell that appears to play a role in pregnancy. As in pregnancy, the key contributors to trophoblast invasion appear to be a unique combination of genes, which appear to regulate multiple components of the interactions between placental and maternal cells, called HLA class 1b genes. The HLA class 1b genes have few alleles, which makes them unlikely to be recognized as foreign by the maternal cells. The low polymorphic properties of these particular HLAs may aid trophoblasts in actively avoiding immune attacks. This review gives a complete description of the mechanisms of interaction between HLAs and maternal uNK cells in humans.

Endometrial Microbiota and Immune Tolerance in Pregnancy

Recent studies have demonstrated that the uterus has its own microbiota. However, there is no consensus on endometrial microbiota composition, thus its role in the healthy uterine environment is still a frontier topic. Endometrial receptivity is key to embryo implantation, and in this specific context immunological tolerance against fetal antigens and the tightly regulated expression of inflammatory mediators are fundamental. According to recent evidence, endometrial microbiota may interact in a very dynamic way with the immune system during the peri-conceptional stage and later during pregnancy. For this reason, a condition of dysbiosis might lead to adverse pregnancy outcomes. The aim of this review is to summarize the evidence on the molecular mechanisms by which the endometrial microbiota may interact with the immune system. For this purpose, the link between dysbiosis and reproductive disorders, such as infertility, recurrent pregnancy loss (RPL), and preterm birth, will be discussed. In conclusion, the most recent findings from molecular analyses will be reported to illustrate and possibly overcome the intrinsic limitations of uterine microbiota detection (low endometrial biomass, high risk of contamination during sampling, and lack of standardization).

Interaction of tumor‑associated macrophages with stromal and immune components in solid tumors: Research progress (Review)

Tumor‑associated macrophages (TAMs) are crucial cells of the tumor microenvironment (TME), which belong to the innate immune system and regulate primary tumor growth, immunosuppression, angiogenesis, extracellular matrix remodeling and metastasis. The review discusses current knowledge of essential cell‑cell interactions of TAMs within the TME of solid tumors. It summarizes the mechanisms of stromal cell (including cancer‑associated fibroblasts and endothelial cells)‑mediated monocyte recruitment and regulation of differentiation, as well as pro‑tumor and antitumor polarization of TAMs. Additionally, it focuses on the perivascular TAM subpopulations that regulate angiogenesis and lymphangiogenesis. It describes the possible mechanisms of reciprocal interactions of TAMs with other immune cells responsible for immunosuppression. Finally, it highlights the perspectives for novel therapeutic approaches to use combined cellular targets that include TAMs and other stromal and immune cells in the TME. The collected data demonstrated the importance of understanding cell‑cell interactions in the TME to prevent distant metastasis and reduce the risk of tumor recurrence.

Interactions between Macrophages and Mast Cells in the Female Reproductive System

Mast cells (MCs) and macrophages (Mϕs) are innate immune cells that differentiate from early common myeloid precursors and reside in all body tissues. MCs have a unique capacity to neutralize/degrade toxic proteins, and they are hypothesized as being able to adopt two alternative polarization profiles, similar to Mϕs, with distinct or even opposite roles. Mϕs are very plastic phagocytic cells that are devoted to the elimination of senescent/anomalous endogenous entities (to maintain tissue homeostasis), and to the recognition and elimination of exogenous threats. They can adopt several functional phenotypes in response to microenvironmental cues, whose extreme profiles are the inflammatory/killing phenotype (M1) and the anti-inflammatory/healing phenotype (M2). The concomitant and abundant presence of these two cell types and the partial overlap of their defensive and homeostatic functions leads to the hypothesis that their crosstalk is necessary for the optimal coordination of their functions, both under physiological and pathological conditions. This review will examine the relationship between MCs and Mϕs in some situations of homeostatic regulation (menstrual cycle, embryo implantation), and in some inflammatory conditions in the same organs (endometriosis, preeclampsia), in order to appreciate the importance of their cross-regulation.

HLA-G genetic diversity and evolutive aspects in worldwide populations

HLA-G is a promiscuous immune checkpoint molecule. The HLA-G gene presents substantial nucleotide variability in its regulatory regions. However, it encodes a limited number of proteins compared to classical HLA class I genes. We characterized the HLA-G genetic variability in 4640 individuals from 88 different population samples across the globe by using a state-of-the-art method to characterize polymorphisms and haplotypes from high-coverage next-generation sequencing data. We also provide insights regarding the HLA-G genetic diversity and a resource for future studies evaluating HLA-G polymorphisms in different populations and association studies. Despite the great haplotype variability, we demonstrated that: (1) most of the HLA-G polymorphisms are in introns and regulatory sequences, and these are the sites with evidence of balancing selection, (2) linkage disequilibrium is high throughout the gene, extending up to HLA-A, (3) there are few proteins frequently observed in worldwide populations, with lack of variation in residues associated with major HLA-G biological properties (dimer formation, interaction with leukocyte receptors). These observations corroborate the role of HLA-G as an immune checkpoint molecule rather than as an antigen-presenting molecule. Understanding HLA-G variability across populations is relevant for disease association and functional studies.

Endometrial Immunity for Embryo Implantation and Pregnancy Establishment

The uterus is an organ for raising the fetus, and its lumen is lined by the endometrium. The endometrium is an important site for the implantation and maturation of fertilized eggs. The endometrium undergoes repetitive proliferation, maturation (decidualization), and exfoliation changes every menstrual cycle. At the same time, the number and type of endometrial immunocompetent cells vary during the menstrual cycle. At the implantation stage, the immunocompetent cells occupy approximately half of the endometrial cells. Immunocompetent cells normally eliminate pathogenic microorganisms to protect the body; however, they also promote immune tolerance to accept the fetus during pregnancy. The immunocompetent cells in the uterus can perform both these functions. With the establishment of pregnancy, stimuli from the trophoblast (placenta) and fetus can also change the immune environment of the uterus, and pregnancy can be maintained only when the immune system is well adapted to the stimuli of some hormones and the fetus. Immunity for the establishment of pregnancy is not simple because multiple immunocompetent cells are involved in establishing and maintaining pregnancy. To understand the immune mechanisms associated with the establishment of pregnancy, we have to learn about each immune cell. This review, therefore, discusses the roles and distribution of the immunocompetent cells inside the uterus during menstruation and early pregnancy.

The Interplay Between Reproductive Tract Microbiota and Immunological System in Human Reproduction

In the last decade, the microbiota, i.e., combined populations of microorganisms living inside and on the surface of the human body, has increasingly attracted attention of researchers in the medical field. Indeed, since the completion of the Human Microbiome Project, insight and interest in the role of microbiota in health and disease, also through study of its combined genomes, the microbiome, has been steadily expanding. One less explored field of microbiome research has been the female reproductive tract. Research mainly from the past decade suggests that microbial communities residing in the reproductive tract represent a large proportion of the female microbial network and appear to be involved in reproductive failure and pregnancy complications. Microbiome research is facing technological and methodological challenges, as detection techniques and analysis methods are far from being standardized. A further hurdle is understanding the complex host-microbiota interaction and the confounding effect of a multitude of constitutional and environmental factors. A key regulator of this interaction is the maternal immune system that, during the peri-conceptional stage and even more so during pregnancy, undergoes considerable modulation. This review aims to summarize the current literature on reproductive tract microbiota describing the composition of microbiota in different anatomical locations (vagina, cervix, endometrium, and placenta). We also discuss putative mechanisms of interaction between such microbial communities and various aspects of the immune system, with a focus on the characteristic immunological changes during normal pregnancy. Furthermore, we discuss how abnormal microbiota composition, “dysbiosis,” is linked to a spectrum of clinical disorders related to the female reproductive system and how the maternal immune system is involved. Finally, based on the data presented in this review, the future perspectives in diagnostic approaches, research directions and therapeutic opportunities are explored.

Immunological Role of the Maternal Uterine Microbiome in Pregnancy: Pregnancies Pathologies and Alterated Microbiota

Understanding what happens at the time of embryo implantation has been the subject of significant research. Investigators from many differing fields including maternal fetal medicine, microbiology, genetics, reproductive endocrinology and immunology have all been studying the moment the embryo interacts with the maternal endometrium. A perfect relationship between the uterus and the embryo, mediated by a tightly controlled interaction between the embryo and the endometrium, is required for successful implantation. Any factors affecting this communication, such as altered microbiome may lead to poor reproductive outcomes. Current theories suggest that altered microbiota may trigger an inflammatory response in the endometrium that affects the success of embryo implantation, as inflammatory mediators are tightly regulated during the adhesion of the blastocyst to the epithelial endometrial wall. In this review, we will highlight the various microbiome found during the periconceptual period, the microbiomes interaction with immunological responses surrounding the time of implantation, its effect on implantation, placentation and ultimately maternal and neonatal outcomes.

Role of major histocompatibility complex variation in graft-versus-host disease after hematopoietic cell transplantation

Graft-versus-host disease (GVHD) remains a significant potentially life-threatening complication of allogeneic hematopoietic cell transplantation (HCT). Since the discovery of the human leukocyte antigen (HLA) system over 50 years ago, significant advances have clarified the nature of HLA variation between transplant recipients and donors as a chief etiology of GVHD. New information on coding and non-coding gene variation and GVHD risk provides clinicians with options to consider selected mismatched donors when matched donors are not available. These advances have increased the availability of unrelated donors for patients in need of a transplant and have lowered the overall morbidity and mortality of HCT.

Cellular Regulation of the Uterine Microenvironment That Enables Embryo Implantation

Implantation of the fertilized egg into the maternal uterus is a crucial step in pregnancy establishment. Increasing evidence suggests that its success depends on various cell types of the innate immune system and on the fine balance between inflammatory and anti-inflammatory processes. In addition, it has recently been established that regulatory T cells play a superordinate role in dictating the quality of uterine environment required for successful pregnancy. Here, we discuss the cellular regulation of uterine receptivity with emphasis on the function and regulation of cells from the innate and adaptive immune system.

Myeloid decidual dendritic cells and immunoregulation of pregnancy: defective responsiveness to Coxiella burnetii and Brucella abortus

Dendritic cells (DCs) are a component of the placental immune system, but their role in pregnancy is still poorly understood. Decidual DCs (dDCs) were selected from at-term pregnancy on the basis of CD14 and CD11c expression. A phenotypic analysis revealed that dDCs are characterized by the expression of monocyte-derived DC (moDCs) markers and specific markers such as HLA-G and its ligand ILT4. As demonstrated by whole-genome microarray, dDCs expressed a specific gene program markedly distinct from that of moDCs; it included estrogen- and progesterone-regulated genes and genes encoding immunoregulatory cytokines, which is consistent with the context of foeto-maternal tolerance. A functional analysis of dDCs showed that they were unable to mature in response to bacterial ligands such as lipopolysaccharide or peptidoglycan, as assessed by the expression of HLA-DR, CD80, CD83, and CD86. When dDCs were incubated with bacteria known for their placenta tropism, Coxiella burnetii and Brucella abortus, they were also unable to mature and to produce inflammatory cytokines. It is likely that the defective maturation of dDCs and their inability to produce inflammatory cytokines is related to the spontaneous release of IL-10 by these cells. Taken together, these results suggest that dDCs exhibit an immunoregulatory program, which may favor the pathogenicity of C. burnetii or B. abortus.

Methylome of fetal and maternal monocytes and macrophages at the feto-maternal interface

PROBLEM

Decidual macrophages (dMφ) of the mother and placental macrophages (Hofbauer cells, HC) of the fetus are deployed at a critical location: the feto-maternal interface. This study was conducted to compare the DNA methylome of maternal and fetal monocytes, dMφ, and HC and thereby to determine the immunobiological importance of DNA methylation in pregnancy.

METHOD OF STUDY

Paired samples were obtained from normal pregnant women at term not in labor and their neonates. Maternal monocytes (MMo) and fetal monocytes (FMo) were isolated from the peripheral blood of mothers and fetal cord blood, respectively. dMφ and HC were obtained from the decidua of fetal membranes and placentas, respectively. DNA methylation profiling was performed using the Illumina Infinium Human Methylation27 BeadChip. Quantitative real-time PCR and Western Blot were performed for validation experiments.

RESULTS

(i) Significant differences in DNA methylation were found in each comparison (MMo versus FMo, 65 loci; dMφ versus HC, 266 loci; MMo versus dMφ, 199 loci; FMo versus HC, 1030 loci). (ii) Many of the immune response-related genes were hypermethylated in fetal cells (FMo and HC) compared to maternal cells (MMo and dMφ). (iii) Genes encoding markers of classical macrophage activation were hypermethylated, and genes encoding alternative macrophage activation were hypomethylated in dMφ and HC compared to MMo and FMo, respectively. (iv) mRNA expressions of DNMT1, DNMT3A, and DNMT3B were significantly lower in dMφ than in HC. (v) 5-azacytidine treatment increased expression of INCA1 in dMφ.

CONCLUSIONS

The findings herein indicate that DNA methylation patterns change during monocyte-macrophage differentiation at the feto-maternal interface. It is also suggested that DNA methylation is an important component of the biological machinery conferring an anti-inflammatory phenotype to macrophages at the feto-maternal interface.

Evolutionary-developmental perspectives on immune system interactions among the pregnant woman, placenta, and fetus, and responses to sexually transmitted infectious agents

A balance has evolved over deep time between the various immune systems of the "triad" that is linked together for a short period: the pregnant woman, the fetus, and the placenta. This balance is affected by, and helps to determine, the immune responses to maternal infectious agents that may be transmitted to the fetus/infant transplacentally, intrapartum, or via breast milk. This review identifies newer evolutionary concepts and processes related particularly to the human placenta, innate and adaptive immune systems involved in tolerance, and in responses to sexually transmitted infectious (STI) agents that may be pathogenic to the fetus/infant at different gestational periods and in the first year of life. An evolutionary-developmental (EVO-DEVO) perspective has been applied to the complexities within, and among, the different actors and their beneficial or deleterious outcomes. Such a phylogenetic and ontogenic approach has helped to stimulate several basic questions and suggested possible explanations and novel practical interventions.

Allele frequencies of human leukocyte antigen-G in a Korean population

The human leukocyte antigen (HLA)-G is a nonclassical major histocompatibility complex class I molecule with relatively limited polymorphism. The differences in allele frequency according to ethnicity and country have not been studied enough, so far. Therefore, fundamental data including allele frequencies and polymorphism are needed for studies on immunological function of HLA-G in each population. We investigated allele frequencies and 14-bp polymorphism of the HLA-G in Koreans. HLA-G alleles and 14-bp polymorphisms were determined by sequence-based typing analysis of exons 2-4 and polymerase chain reaction of exon 8 in 200 unrelated individuals. Genotyping analysis identified eight different HLA-G alleles, which indicates that the Korean population presents limited HLA-G allelic polymorphism. HLA-G*01:01:01:01 and G*01:04:01 were frequent alleles (42.5% and 34.0%), and allelic frequencies were similar to those of other Asian populations. The 14-bp deletion alleles are higher (78%) in Koreans, although the frequencies of the 14-bp insertion/deletion polymorphism have been known to be nearly equal in many Caucasian populations. HLA-G*01:01:08 was reported strong linkage disequilibrium with the 14-bp deletion in a previous report; the same allele was accompanied with 14-bp insertion in our study. There are a few studies investigating allele frequencies, and most of them were studied before high-resolution method era. This is the first study regarding HLA-G genotypes in Korean, which were identified by high-resolution method. From this study, we identified HLA-G frequencies of a Korean population and expect this study could help further investigations for immunological and clinical implications of HLA-G.

Modulation of cytokine and chemokine secretions in rhesus monkey trophoblast co-culture with decidual but not peripheral blood monocyte-derived macrophages

PROBLEM

Decidual macrophages are thought to promote pregnancy success, in part through interactions with invading trophoblast cells in hemochorial placentation. However, the factors that constitute this regulatory cross talk are not well understood.

METHOD OF STUDY

Rhesus monkey decidual and peripheral blood-derived macrophages were co-cultured with primary Rhesus trophoblasts. Macrophage functions including cell-surface marker expression, antigen uptake and processing, in vitro migration, and cytokine and chemokine secretions were evaluated.

RESULTS

While most macrophage functions were unchanged by trophoblast co-culture, changes in the secretion of selected cytokines and the migration of trophoblasts were noted when decidual (but generally, not peripheral blood monocyte-derived) macrophages were cultured with trophoblasts. In addition, basal secretion differed significantly between peripheral blood-derived and decidual macrophages for a broad spectrum of cytokines. When trophoblasts were pre-treated with an anti-Mamu-AG antibody, 25D3, there was no change in cytokine or chemokine secretion.

CONCLUSION

Macrophage cytokine expression can be modulated by trophoblast co-culture, but it remains unclear how Mamu-AG is involved.

Gene expression in placentation of farm animals: an overview of gene function during development

Eutherian mammals share a common ancestor that evolved into two main placental types, i.e., hemotrophic (e.g., human and mouse) and histiotrophic (e.g., farm animals), which differ in invasiveness. Pregnancies initiated with assisted reproductive techniques (ART) in farm animals are at increased risk of failure; these losses were associated with placental defects, perhaps due to altered gene expression. Developmentally regulated genes in the placenta seem highly phylogenetically conserved, whereas those expressed later in pregnancy are more species-specific. To elucidate differences between hemotrophic and epitheliochorial placentae, gene expression data were compiled from microarray studies of bovine placental tissues at various stages of pregnancy. Moreover, an in silico subtractive library was constructed based on homology of bovine genes to the database of zebrafish - a nonplacental vertebrate. In addition, the list of placental preferentially expressed genes for the human and mouse were collected using bioinformatics tools (Tissue-specific Gene Expression and Regulation [TiGER] - for humans, and tissue-specific genes database (TiSGeD) - for mice and humans). Humans, mice, and cattle shared 93 genes expressed in their placentae. Most of these were related to immune function (based on analysis of gene ontology). Cattle and women shared expression of 23 genes, mostly related to hormonal activity, whereas mice and women shared 16 genes (primarily sexual differentiation and glycoprotein biology). Because the number of genes expressed by the placentae of both cattle and mice were similar (based on cluster analysis), we concluded that both cattle and mice were suitable models to study the biology of the human placenta.

Natural killer cells and HLA-G expression in the basal decidua of human placenta adhesiva

Retained placenta is caused by abnormal adherence of the placenta to the uterine wall, leading to delayed expulsion of the placenta and causing postpartum haemorrhage. The mildest form of retained placenta is the placenta adhesiva (PA), of which the cause is unknown. The aim of our study was to explore possible differences in immune response in the basal decidua between PA and control placentas (CP). We performed a descriptive analysis of immunohistochemical differences in 17 PA and 10 CP. Our results show that in PA the amount of uterine natural killer (uNK) cells is significantly reduced (0.2 uNK cell/standardised area) as compared to CP (9.8 uNK cell/standardised area, p < 0.001) whereas the number of trophoblast cells and the expression of HLA-G by trophoblast are similar in the decidua of PA and CP. We speculate that adequate numbers of uNK cells in the basal decidua are needed for normal expulsion of the placenta.

The immunomodulatory roles of macrophages at the maternal-fetal interface

Macrophages are versatile cells that play a central role in innate and adaptive immunity and participate in a wide variety of biological processes. In the uterine decidua, macrophages represent a major leukocyte subset throughout pregnancy. Here, decidual macrophages exert an immunosuppressive phenotype characterized by abundant production of interleukin (IL)-10 and indoleamine 2,3-dioxygenase activity. Their polarized cytokine secretion pattern has recently been classified as an M2 phenotype. These features of decidual macrophages favor maternal immune tolerance to semiallogenic fetus. In addition, macrophages cooperate with trophoblast cells during the early stages of human pregnancy to support uterine vasculature remodeling by removing apoptotic cells and through the production of proteases that degrade the extracellular matrix. In the peripartum period, macrophages also participate in the regulation of cervical ripening and the initiation of parturition through the production of proinflammatory cytokines and prostaglandin E(2) (PGE(2)). Aberrant activity of uterine macrophages is linked to the pathogenesis of preeclampsia and preterm delivery. Here, we review the immunomodulatory roles of decidual macrophages during pregnancy.

Amniotic fluid soluble human leukocyte antigen-G in term and preterm parturition, and intra-amniotic infection/inflammation

OBJECTIVE

Circulating soluble human leukocyte antigen-G (sHLA-G) has been associated with pregnancy complications, and determination of sHLA-G concentrations in amniotic fluid (AF) has been reported in normal pregnancies. Our aim was to determine if the AF concentrations of sHLA-G change with advancing gestation, spontaneous labor at term, and in patients with spontaneous preterm labor (PTL) with intact membranes, as well as in those with preterm prelabor rupture of membranes (PROM), in the presence or absence of intra-amniotic infection/inflammation (IAI).

STUDY DESIGN

This cross-sectional study included the following groups: (1) mid-trimester (n = 55); (2) normal pregnancy at term with (n = 50) and without (n = 50) labor; (3) spontaneous PTL with intact membranes divided into: (a) PTL who delivered at term (n = 153); (b) PTL who delivered preterm without IAI (n = 108); and (c) PTL with IAI (n = 84); and (4) preterm PROM with (n = 46) and without (n = 44) IAI. sHLA-G concentrations were determined by ELISA. Non-parametric statistics were used for analysis.

RESULTS

(1) Among patients with PTL, the median AF sHLA-G concentration was higher in patients with IAI than in those without IAI or women that delivered at term (p < 0.001 for both comparisons); (2) Similarly, patients with preterm PROM and IAI had higher median AF sHLA-G concentrations than those without IAI (p = 0.004); (3) Among patients with PTL and delivery, those with histologic chorioamnionitis and/or funisitis had a higher median AF sHLA-G concentration than those without histologic inflammation (p < 0.001); and (4) The median AF sHLA-G concentration did not change with advancing gestational age.

CONCLUSIONS

AF sHLA-G concentrations are elevated in preterm parturition associated to IAI as well as in histologic chorioamnionitis. We propose that sHLA-G may participate in the regulation of the host immune response against intra-amniotic infection.

Toll-like receptor-4 (TLR4) mediates human beta-defensin-2 (HBD-2) induction in response to Chlamydia pneumoniae in mononuclear cells

Monocytes are pivotal effector cells of the innate immune system that are vital for recognizing and eliminating invasive microbial pathogens. When microbial products bind to pathogen-recognition receptors, monocytes are activated and release a broad array of cytokines and defensins that orchestrate the host innate and adaptive immune responses. The aim of the present study is to investigate whether Toll-like receptor-4 (TLR4) mediates human beta-defensin-2 (HBD-2) induction in response to Chlamydia pneumoniae in mononuclear cells. We showed that TLR4 is expressed in U937 cells and monocytes infected with viable microorganisms in a time-dependent fashion, while heat-inactivated microorganisms induced a lesser expression, albeit still significant, of TLR4 compared with viable organisms; flow cytometric analysis, in particular, revealed a higher level of TLR4 expression at 48 and 72 h postinfection. In addition, U937 cells and monocytes responded to C. pneumoniae in a TLR4-dependent manner with induction of mRNA and protein of the antimicrobial peptide HBD-2. The treatment of cells with TLR4-neutralizing antibody resulted in a decrease in C. pneumoniae-induced HBD-2 production. This study reveals that TLRs not only recognize ligands but also the types of effector molecules induced, namely, antimicrobial peptides. An understanding of the importance of the TLR-mediated antimicrobial mechanisms may provide new avenues for the development of therapeutic regimens aimed at activating the body's own defenses by stimulating TLR-dependent pathways.

Characterization of decidual leukocyte populations in cynomolgus and vervet monkeys

The objective of this study was the phenotypic and functional evaluation of decidual immune cells in the cynomolgus and vervet monkeys. Early pregnancy (days 36-42) deciduas were obtained by fetectomy for histological evaluation and decidual mononuclear leukocyte (MNL) isolation. While peripheral NK (pNK) cells in these species do not express CD56, CD56(+) NK cells were abundant in decidual samples. The majority of decidual NK (dNK) cells (>80%) had high light-scatter characteristics and were CD56(bright)CD16(+) cells with no or very low levels of natural cytotoxicity receptors (NKp46, NKp30) and NKG2A, while a minor population were small CD56(dim)CD16(-) lymphocytes also expressing less NKp46, NKp30 and NKG2A than pNK cells. All dNK cells were found to be perforin(+); however, their cytotoxic potential was low and cynomolgus dNK cells showed strongly reduced cytotoxicity against target cells compared with pNK cells. Macrophages and T cells together comprised approximately 25-30% of decidual MNL. Decidual T cells contained a higher proportion of the minor T cell subtypes (gammadeltaT cells, CD56(+) T cells) compared with peripheral blood. A subset of DC-SIGN(+) macrophages, with a distribution adjacent to areas of placental attachment in contrast to the widespread setting of general CD68(+) cells, was identified in both species. Together, these results demonstrate that the maternal-fetal interface in both cynomolgus and vervet monkeys is very rich in immune cells that have similar phenotypes to those seen in humans, indicating that both species are excellent models to study the contributions of distinct immune cell populations to pregnancy support.

Placental cytokine expression covaries with maternal asthma severity and fetal sex

In the presence of maternal asthma, we have previously reported reduced placental blood flow, decreased cortisol metabolism, and reductions in fetal growth in response to maternal asthma and asthma exacerbations. We have proposed that these changes in placental function and fetal development may be related to activation of proinflammatory pathways in the placenta in response to maternal asthma. In the present study, we examined the influence of maternal asthma severity, inhaled glucocorticoid treatment, maternal cigarette use, placental macrophage numbers, and fetal sex on placental cytokine mRNA expression from a prospective cohort study of pregnant women with and without asthma. Placental expression of TNF-alpha, IL-1beta, IL-6, IL-8, and IL-5 mRNA were all increased significantly in placentae of female fetuses whose mothers had mild asthma, but no changes were observed in placentae of male fetuses. The proinflammatory cytokines TNF-alpha, IL-1beta, and IL-6 were negatively correlated with female cord blood cortisol, but there were no such correlations in placentae from males. Multivariate analysis indicated the strongest predictor of both cytokine mRNA expression in the placenta and birth weight was fetal cortisol but only in females. Placental cytokine mRNA levels were not significantly altered by inhaled glucocorticoid use, placental macrophage numbers, cigarette use, moderate-severe asthma, or male sex. These data suggest that placental basal cytokine mRNA expression is sex specifically regulated in pregnancies complicated by asthma, and interestingly these changes are more prevalent in mild rather than severe asthma.

Antigen-presenting cells and materno-fetal tolerance: an emerging role for dendritic cells

During pregnancy, a delicate balance of innate and adaptive immune responses at the maternal-fetal interface promotes survival of the semi-allogeneic embryo and, at the same time, allows effective immunity to protect the mother from environmental pathogens. As in other tissues, antigen handling and processing in the decidualized endometrium constitutes a primary event in the onset of immune responses and is therefore likely to determine their stimulatory or tolerogenic nature. Maternal antigen-presenting cells [macrophages and dendritic cells (DCs)] are scattered throughout the decidualized endometrium during all stages of pregnancy and appear to be important players in this feto-maternal immune adjustment. This review focuses on the characterization of decidual macrophages and DCs, as well as their involvement in cell-cell interactions within the decidual leukocyte network, which are likely to influence uterine and placental homeostasis as well as the local maternal immune responses to the fetus during pregnancy.

Absence of the HLA-G*0105N allele in Amerindian populations from the Brazilian Amazon Region: a possible role of natural selection

The human leukocyte antigen G (HLA-G) null allele (G*0105N) is defined by a DeltaC deletion at exon 3. Its high frequency in populations from areas with high pathogen loads and the putative role of HLA-G in placental development suggest that the reduced G1 expression in G*0105N heterozygous placentas may improve the intrauterine defense against infections. The G*0105N allele frequencies were evaluated in 143 Amerindians from six isolated tribes that inhabit the Central Amazon to determine the existence of genotype frequencies that suggest balancing selection in favor of G*0105N heterozygotes. No copy of the null allele was found by exon 3 sequencing. Although this finding may be because of demographic or other selective factors, it also suggests no evidence of G*0105N heterozygous advantage.

HLA-G alleles and HLA-G 14 bp polymorphisms in a Brazilian population

Brazilians represent one of the most heterogeneous populations in the world as the result of five centuries of interethnic crosses. We investigated the polymorphism of the HLA-G locus in a Brazilian urban sample. HLA-G alleles were determined by SBT analysis of exons 2-4 and 8 in 103 unrelated individuals. The genotyping analysis identified 11 different HLA-G alleles, including the recently described G*010110 allele, and four new variants in this population. These data indicate that this Brazilian population presents high HLA-G allelic polymorphism, suggesting increased levels of intrapopulational genetic diversity that may be because of the admixed nature of the sample. This is the first study regarding HLA-G genotyping that was performed at such refined resolution level in this heterogeneous population.

The role of macrophage migration inhibitory factor in maintaining the immune privilege at the fetal–maternal interface

Macrophage migration inhibitory factor (MIF) is a pivotal regulator of the innate and adaptive immunity affecting the response and behavior of macrophages and lymphocytes. MIF is also implicated in other fundamental cellular processes including angiogenesis and cell proliferation. Several studies examined the expression of MIF in reproductive organs and tissues and its involvement in different aspects of human and animal reproduction. The goal of this review was to summarize these findings and discuss, in particular, the role of MIF in the maintenance of the immune privilege at the human fetal-maternal interface.

Maternal asthma during pregnancy and fetal outcomes: potential mechanisms and possible solutions

PURPOSE OF REVIEW

Asthma exacerbations during pregnancy can be a serious complication that have detrimental consequences for both mother and fetus. The pathophysiological mechanisms that cause worsening asthma during pregnancy are only just starting to be examined. This review will examine the recent literature on immune function in pregnant women, immune function in nonpregnant asthma patients and studies conducted on asthma during pregnancy.

RECENT FINDINGS

Fifty-five percent of women with asthma will experience at least one exacerbation during pregnancy. This has significant effects on fetal growth and survival, especially if the fetus is male. A number of factors that may contribute to the development of worsening asthma during pregnancy include pregnancy-induced changes in maternal immune function, increased maternal susceptibility to infection, female fetal sex, noncompliance with medication and prepregnancy asthma severity. Interestingly, the immune changes in the maternal system in response to the presence of the fetus and placenta are very similar to the immune changes described in nonpregnant asthma patients with noneosinophilic asthma.

SUMMARY

These studies highlight that worsening asthma during pregnancy cannot be attributed to pregnancy alone or asthma alone and may be a complex combination of factors and events.

Inhibition of term decidual NK cell cytotoxicity by soluble HLA-G1

OBJECTIVES

Soluble (s)HLA-G1 is produced by trophoblast cells. Aim was to analyze the capacities and mechanisms of sHLA-G1 to regulate interleukin (IL)-2-induced cytotoxicity of natural killer (NK) cells from human deciduas.

METHODS

Natural killer cells were isolated from decidual layers of term placentae, stimulated or not with IL-2 and supplemented with various concentrations of recombinant soluble HLA-G1 (sHLA-G1). For NK cell cytotoxicity assays, K562 cells were used as targets. Expression of signal transducer and activator of transcription 3 (STAT3) and perforin was analyzed by Western blotting. Apoptosis was examined by assessment of poly(ADP-ribose) polymerase cleavage. NK cells were analyzed by flow cytometry for IL-2receptor-alpha (IL-2R alpha; CD25) and transferrin receptor CD71 expression.

RESULTS

Interleukin-2 increases CD71, STAT3, perforin expression and cytotoxic potential of NK cells. Expression of CD71, STAT3 and perforin decreased simultaneously with cytotoxicity and dose-dependently when sHLA-G1 (1.6 micro g/mL-1.6 ng/mL) was added to IL-2 stimulated cultures. sHLA-G1 did not induce apoptosis and CD25 expression was not affected.

CONCLUSION

Interleukin-2R alpha expression is not controlled by sHLA-G1, but its signal transducer STAT3 as well as several downstream effects, such as perforin expression, proliferation and cytotoxicity. The control of STAT3 bioavailability through sHLA-G1 may be a key regulator of the mentioned effects.

Plasma soluble human leukocyte antigen G levels in asthmatic children

BACKGROUND

Human leukocyte antigen G (HLA-G) is a nonclassical major histocompatibility complex class I gene. HLA-G stimulates Th2 cytokine secretion by peripheral blood mononuclear cells. The role of soluble HLA-G (sHLA-G) in bronchial asthma is incompletely understood and the plasma level of sHLA-G in asthmatic children has not been investigated.

OBJECTIVE

It was the aim of this study to investigate the plasma level of sHLA-G in asthmatic children.

METHODS

Asthmatic (n = 53) and healthy children (n = 16) were included in the study. Levels of sHLA-G were determined in plasma using ELISA. Spirometry, total immunoglobulin E and eosinophil counts were obtained and skin testing done with a battery of 25 antigens with appropriate positive and negative controls.

RESULTS

No significant difference was observed in the plasma level of sHLA-G between the asthmatic and healthy children (p > 0.05). When we compared atopic asthmatics with healthy controls, we found significantly higher levels of sHLA-G in atopic asthmatics (p < 0.05). There was a significant difference in the peripheral blood eosinophil counts and total immunoglobulin E levels among the groups (p < 0.001).

CONCLUSION

Our study shows that plasma sHLA-G levels do not differ between asthmatic children and healthy controls. However, higher plasma levels of sHLA-G in atopic asthmatics may suggest a role for sHLA-G in atopy. Further investigations are required to better define the mechanism of the production and the role of sHLA-G molecules observed in patients with asthma.

Lipopolysaccharide-induced IL-1 beta production by human uterine macrophages up-regulates uterine epithelial cell expression of human beta-defensin 2

The uterine endometrium coordinates a wide spectrum of physiologic and immunologic functions, including endometrial receptivity and implantation as well as defense against sexually transmitted pathogens. Macrophages and epithelial cells cooperatively mediate innate host defense against bacterial invasion through the generation of immunologic effectors, including cytokines and antimicrobial peptides. In this study, we demonstrate that stimulation of peripheral blood monocytes and uterine macrophages with bacterial LPS induces the production of biologically active proinflammatory IL-1beta. High doses of estradiol enhance LPS-induced IL-1beta expression in an estrogen receptor-dependent manner. Furthermore, both peripheral blood monocyte- and uterine macrophage-derived IL-1beta induce secretion of antimicrobial human beta-defensin 2 by uterine epithelial cells. These data indicate dynamic immunologic interaction between uterine macrophages and epithelial cells and implicate a role for estradiol in the modulation of the immune response.

Immune interactions at the maternal–fetal interface

Models of murine allogeneic pregnancy have established that maternal T cells recognize fetal alloantigens and are normally suppressed or deleted. While the precise cellular interactions and mechanisms involved in maternal lymphocyte tolerance are not yet clear, the identity of some of the critical factors are beginning to be uncovered. Signals that have been shown in mice to have an obligatory role in immunological survival of the semiallogeneic fetus include, but are probably not limited to, indoleamine-2,3-dioxygenase and the newly discovered B7 family protein, B7-H1. Whether these proteins have intersecting functions is unknown, but it is possible that both are involved in the control of maternal T regulatory cells, which are also strictly required for successful allogeneic pregnancy in mice. Additional factors that are involved include trophoblast and/or maternally derived FasL, and in humans, class Ib HLA molecules. The potency of these mechanisms in protecting the fetal allograft is underscored by the scarcity of knockout and transgenic models in which pregnancy is immunologically compromised. Here, the current understanding of mechanisms of specific suppression of maternal lymphocytes is reviewed.