Regulation of major histocompatibility complex class II gene expression in trophoblast cells

Alpha-Fetoprotein as a Factor of Differentiation and Functional Activity of Myeloid-Derived Suppressor Cells

We studied the role of alpha-fetoprotein (AFP) in regulation of differentiation and functional activity of human myeloid-derived suppressor cells (MDSC) in vitro. To obtain MDSC, CD11b+ cells were isolated from the peripheral blood of healthy donors followed by cytokine induction (IL-1β+GM-CSF) into the MDSC phenotype. The cell functions were assessed by the expression of indoleamine 2,3-dioxygenase (IDO) and arginase-1 (Arg1) and cytokine profile of the cell cultures. Native AFP did not affect the total number of MDSC and the percentage of polymorphonuclear MDSC (PMN-MDSC), but increased the number of monocytic MDSC (M-MDSC). AFP did not change the expression of Arg1, but in low concentrations (10 and 50 U/ml) increased the number of IDO-containing cells. AFP modulated the cytokine profile of CD11b+ cells: it reliably decreased the level of IL-19 (50 and100 U/ml) and showed a tendency to decrease the levels of IL-34, MMP-2, sCD163, CHI3L1, OPN and to increase the levels of IL-29, IL-32, APRIL, PTX3, and sTNF-R1. Thus, we have demonstrated a regulatory effect of native AFP at the level of MDSC generated from CD11b+ cells under conditions of cytokine induction in vitro.

Immunopeptidome profiling of human coronavirus OC43-infected cells identifies CD4 T-cell epitopes specific to seasonal coronaviruses or cross-reactive with SARS-CoV-2

Seasonal "common-cold" human coronaviruses are widely spread throughout the world and are mainly associated with mild upper respiratory tract infections. The emergence of highly pathogenic coronaviruses MERS-CoV, SARS-CoV, and most recently SARS-CoV-2 has prompted increased attention to coronavirus biology and immunopathology, but the T-cell response to seasonal coronaviruses remains largely uncharacterized. Here we report the repertoire of viral peptides that are naturally processed and presented upon infection of a model cell line with seasonal coronavirus OC43. We identified MHC-bound peptides derived from each of the viral structural proteins (spike, nucleoprotein, hemagglutinin-esterase, membrane, and envelope) as well as non-structural proteins nsp3, nsp5, nsp6, and nsp12. Eighty MHC-II bound peptides corresponding to 14 distinct OC43-derived epitopes were identified, including many at very high abundance within the overall MHC-II peptidome. Fewer and less abundant MHC-I bound OC43-derived peptides were observed, possibly due to MHC-I downregulation induced by OC43 infection. The MHC-II peptides elicited low-abundance recall T-cell responses in most donors tested. In vitro assays confirmed that the peptides were recognized by CD4+ T cells and identified the presenting HLA alleles. T-cell responses cross-reactive between OC43, SARS-CoV-2, and the other seasonal coronaviruses were confirmed in samples of peripheral blood and peptide-expanded T-cell lines. Among the validated epitopes, spike protein S903-917 presented by DPA1*01:03/DPB1*04:01 and S1085-1099 presented by DRB1*15:01 shared substantial homology to other human coronaviruses, including SARS-CoV-2, and were targeted by cross-reactive CD4 T cells. Nucleoprotein N54-68 and hemagglutinin-esterase HE128-142 presented by DRB1*15:01 and HE259-273 presented by DPA1*01:03/DPB1*04:01 are immunodominant epitopes with low coronavirus homology that are not cross-reactive with SARS-CoV-2. Overall, the set of naturally processed and presented OC43 epitopes comprise both OC43-specific and human coronavirus cross-reactive epitopes, which can be used to follow CD4 T-cell cross-reactivity after infection or vaccination, and to guide selection of epitopes for inclusion in pan-coronavirus vaccines.

Seahorse Male Pregnancy as a Model System to Study Pregnancy, Immune Adaptations, and Environmental Effects

Seahorses, together with sea dragons and pipefishes, belong to the Syngnathidae family of teleost fishes. Seahorses and other Syngnathidae species have a very peculiar feature: male pregnancy. Among different species, there is a gradation of paternal involvement in carrying for the offspring, from a simple attachment of the eggs to the skin surface, through various degrees of egg coverage by skin flaps, to the internal pregnancy within a brood pouch, which resembles mammalian uterus with the placenta. Because of the gradation of parental involvement and similarities to mammalian pregnancy, seahorses are a great model to study the evolution of pregnancy and the immunologic, metabolic, cellular, and molecular processes of pregnancy and embryo development. Seahorses are also very useful for studying the effects of pollutants and environmental changes on pregnancy, embryo development, and offspring fitness. We describe here the characteristics of seahorse male pregnancy, its regulatory mechanisms, the development of immune tolerance of the parent toward the allogeneic embryos, and the effects of environmental pollutants on pregnancy and embryo development.

Placental Extracellular Vesicles Can Be Loaded with Plasmid DNA

Recently, extracellular vesicles (EVs) have garnered considerable interest as potential vehicles for drug delivery, including gene therapy. Although EVs from diverse sources have been investigated, current techniques used in the field for EV generation limit large-scale EV production. The placenta is essentially a tissue transplant and has unique properties that allow it to avoid the maternal immune system making it likely that placental EVs will not generate inflammatory responses and will avoid clearance by the immune system. We propose that placental EVs produced from explant cultures are an efficient method to produce considerable quantities of EVs that would be safe to administer, and we hypothesize that placental EVs can be loaded with large exogenous plasmids. To this end, we trialed three strategies to load plasmid DNA into placental EVs, including loading via electroporation of placental tissue prior to EV isolation and loading directly into placental EVs via electroporation or direct incubation of the EVs in plasmid solution. We report that the placenta releases vast quantities of EVs compared to placental cells in monolayer cultures. We show successful loading of plasmid DNA into both large- and small-EVs following both exogenous loading strategies with more plasmid encapsulated in large-EVs. Importantly, direct incubation did not alter EV size nor quantity. Further, we showed that the loading efficiency into EVs was dependent on the exogenous plasmid DNA dose and the DNA size. These results provide realistic estimates of plasmid loading capacity into placental EVs using current technologies and showcase the potential of placental EVs as DNA delivery vehicles.

Neurotrophins: are they involved in immune tolerance in pregnancy?

In this review, an attempt was made to substantiate the possibility for neurotrophins to be involved in the development of immune tolerance based on data accumulated on neurotrophin content and receptor expression in the trophoblast and immune cells, in particular, in natural killer cells. Numerous research results are reviewed to show that the expression and localization of neurotrophins along with their high-affinity tyrosine kinase receptors and low-affinity p75NTR receptor in the mother-placenta-fetus system indicate the important role of neurotrophins as binding molecules in regulating the crosstalk between the nervous, endocrine, and immune systems in pregnancy. An imbalance between these systems can occur with tumor growth and pathological processes observed in pregnancy complications and fetal development anomalies.

Immunopeptidome profiling of human coronavirus OC43-infected cells identifies CD4 T cell epitopes specific to seasonal coronaviruses or cross-reactive with SARS-CoV-2

Seasonal "common-cold" human coronaviruses are widely spread throughout the world and are mainly associated with mild upper respiratory tract infections. The emergence of highly pathogenic coronaviruses MERS-CoV, SARS-CoV, and most recently SARS-CoV-2 has prompted increased attention to coronavirus biology and immunopathology, but identification and characterization of the T cell response to seasonal human coronaviruses remain largely uncharacterized. Here we report the repertoire of viral peptides that are naturally processed and presented upon infection of a model cell line with seasonal human coronavirus OC43. We identified MHC-I and MHC-II bound peptides derived from the viral spike, nucleocapsid, hemagglutinin-esterase, 3C-like proteinase, and envelope proteins. Only three MHC-I bound OC43-derived peptides were observed, possibly due to the potent MHC-I downregulation induced by OC43 infection. By contrast, 80 MHC-II bound peptides corresponding to 14 distinct OC43-derived epitopes were identified, including many at very high abundance within the overall MHC-II peptidome. These peptides elicited low-abundance recall T cell responses in most donors tested. In vitro assays confirmed that the peptides were recognized by CD4+ T cells and identified the presenting HLA alleles. T cell responses cross-reactive between OC43, SARS-CoV-2, and the other seasonal coronaviruses were confirmed in samples of peripheral blood and peptide-expanded T cell lines. Among the validated epitopes, S 903-917 presented by DPA1*01:03/DPB1*04:01 and S 1085-1099 presented by DRB1*15:01 shared substantial homology to other human coronaviruses, including SARS-CoV-2, and were targeted by cross-reactive CD4 T cells. N 54-68 and HE 128-142 presented by DRB1*15:01 and HE 259-273 presented by DPA1*01:03/DPB1*04:01 are immunodominant epitopes with low coronavirus homology that are not cross-reactive with SARS-CoV-2. Overall, the set of naturally processed and presented OC43 epitopes comprise both OC43-specific and human coronavirus cross-reactive epitopes, which can be used to follow T cell cross-reactivity after infection or vaccination and could aid in the selection of epitopes for inclusion in pan-coronavirus vaccines.

Author Summary

There is much current interest in cellular immune responses to seasonal common-cold coronaviruses because of their possible role in mediating protection against SARS-CoV-2 infection or pathology. However, identification of relevant T cell epitopes and systematic studies of the T cell responses responding to these viruses are scarce. We conducted a study to identify naturally processed and presented MHC-I and MHC-II epitopes from human cells infected with the seasonal coronavirus HCoV-OC43, and to characterize the T cell responses associated with these epitopes. We found epitopes specific to the seasonal coronaviruses, as well as epitopes cross-reactive between HCoV-OC43 and SARS-CoV-2. These epitopes should be useful in following immune responses to seasonal coronaviruses and identifying their roles in COVID-19 vaccination, infection, and pathogenesis.

Cellular Complexity of Hemochorial Placenta: Stem Cell Populations, Insights from scRNA-seq, and SARS-CoV-2 Susceptibility

Purpose of Review

The placenta is a transient organ that forms de novo and serves a critical role in supporting fetal growth and development. Placental oxygen, nutrients, and waste are transported through processes that depend on vascular structure and cell type-specific expression and localization of membrane transporters. Understanding how the placenta develops holds great significance for maternal-fetal medicine. The purpose of this review is to examine current information regarding placental progenitor populations.

Recent Findings

Recent advancements in single-cell RNA sequencing (scRNA-seq) provide unprecedented depth for the investigation of cell type-specific gene expression patterns in the placenta. Thus far, several mouse placenta scRNA-seq studies have been conducted which produced and analyzed transcriptomes of placental progenitors and cells of the fully developed placenta between embryonic day (E) 7.0 and E12.5. Together with human placenta scRNA-seq data which, in part, has been produced through coordinated research campaigns in the scientific community to understand the potential for SARS-CoV-2 infection, these mammalian studies lend fundamental insight into the cellular and molecular composition of hemochorial placentae found in both mouse and human.

Summary

Single-cell placenta research has advanced understanding of tissue-resident stem cells and molecules that are poised to support maternal-fetal communication and nutrient transport. Herein, we provide context for these recent findings by reviewing placental anatomy and cell populations, and discuss recent scRNA-seq mouse placenta findings. Further research is needed to evaluate the utility of placental stem cells in the development of new therapeutic approaches for the treatment of wound healing and disease.

Fetomaternal Immune Tolerance: Crucial Mechanisms of Tolerance for Successful Pregnancy in Humans

For many years, the question of how the maternal immune system tolerates the foreign fetus has remained unanswered, and numerous studies have considerably attempted to elucidate underlying mechanisms for fetomaternal tolerance. This review aimed at discussing various significant mechanisms in fetomaternal compatibility. At the fetomaternal interface, in addition to having efficient control against infections, innate and adaptive maternal immune systems selectively prevent fetal rejection. In general, understanding the complex mechanisms of fetomaternal tolerance is critical for immunologic tolerance induction and spontaneous abortion prevention in high-risk populations. Different cells and molecules, such as regulatory T-cells, dendritic cells, decidua cells, IDO, Class I HLA molecules, TGF-β, and IL-10, induce maternal immune tolerance in the fetus in numerous ways. The findings on fetomaternal immune tolerance have remained controversial and require further research.

Role of Human Leukocyte Antigens at the Feto-Maternal Interface in Normal and Pathological Pregnancy: An Update

The successful maternal tolerance of the semi-allogeneic fetus provides an apparent immunologic paradox. Indeed, deep invasion of placental trophoblast cells into maternal uterine tissue and the following growth of the fetus have to be tolerated by a pregnant woman’s immune system. Among the various possible protective mechanisms that may be involved in human pregnancy, the expression of a non-classical pattern of human leukocyte antigen (HLA) class I molecules and the complete lack of expression of HLA class II molecules in placental tissues seem to be the most relevant mechanisms of fetal escape from maternal immune recognition. The importance of HLA molecules in fetal toleration by the maternal immune system is highlighted by pregnancy complications occurring in cases of abnormal HLA molecule expression at the maternal–fetal interface. In this review, we summarize evidences about the role of placental HLA molecules in normal and pathological pregnancies.

Embryo-maternal communication in dogs: Immune system related factors

In the bitch, establishment of pregnancy is believed to be mainly initiated by the free-floating embryo in the uterus that is under progesterone influence. As in other species, the active participation of the embryo is no longer questioned. Secretory products are transported to the embryo-maternal interface and contribute to extra-cellular matrix (ECM) degradation, a change in the intrauterine immune milieu towards a reduction of immune cells and a change in lymphocyte subsets, cell differentiation, angiogenesis, and the balance between proliferation and apoptosis. For cell-to-cell communication between embryo and maternal tissue, biomolecules inclusive microRNAs might be transported and exchanged via extracellular vesicles (EVs) as in other species. Maternal acceptance of the fetal allograft is vital for the establishment of pregnancy. Findings so far indicate that the embryo avoids attacks from the maternal system via passive and active mechanisms. One hypothesis is that expression or suppression of surface molecules help the canine embryo to hide from the maternal immune system on one side and to actively destroy cytotoxic immune cells on the other side; there are further clues that the canine embryo blocks activation of intrauterine leukocytes. Intracellular repair mechanisms via heat shock proteins (HSP) are candidates under investigation. The presence and function of immunomodulatory intrauterine cells like Treg cells and their interaction with the embryo have been intensely studied in other species but remains to be investigated in the canine preimplantation uterus.

Dynamics of trophoblast differentiation in peri-implantation-stage human embryos

Single-cell RNA sequencing of cells from cultured human blastocysts has enabled us to define the transcriptomic landscape of placental trophoblast (TB) that surrounds the epiblast and associated embryonic tissues during the enigmatic day 8 (D8) to D12 peri-implantation period before the villous placenta forms. We analyzed the transcriptomes of 3 early placental cell types, cytoTB (CTB), syncytioTB (STB), and migratoryTB (MTB), picked manually from cultured embryos dissociated with trypsin and were able to follow sublineages that emerged from proliferating CTB at the periphery of the conceptus. A unique form of CTB with some features of STB was detectable at D8, while mature STB was at its zenith at D10. A form of MTB with a mixed MTB/CTB phenotype arose around D10. By D12, STB generation was in decline, CTB had entered a new phase of proliferation, and mature MTB cells had begun to move from the main body of the conceptus. Notably, the MTB transcriptome at D12 indicated enrichment of transcripts associated with IFN signaling, migration, and invasion and up-regulation of HLA-C, HLA-E, and HLA-G. The STB, which is distinct from the STB of later villous STB, had a phenotype consistent with intense protein export and placental hormone production, as well as migration and invasion. The studies show that TB associated with human embryos is in rapid developmental flux during peri-implantation period when it must invade, signal robustly to the mother to ensure that the pregnancy continues, and make first contact with the maternal immune system.

HLA-DR is aberrantly expressed at feto-maternal interface in pre-eclampsia

In normal pregnancy, villous cytotrophoblast and syncytiotrophoblast do not express HLA Class I and Class II molecules, while invasive extravillous trophoblast only express class I HLA-C and the atypical class Ib antigens, HLA-G, -E and -F. Inadequate maternal tolerance of invasive trophoblast has been proposed as a possible immunologic trigger of poor trophoblast invasion and subsequent occurrence of pre-eclampsia. This study aimed to investigate possible aberrant expression of class II HLA-DR on placentae and syncytiotrophoblast-derived extracellular vesicles (STEVs), obtained by dual placental perfusion, from pre-eclampsia (n = 23) and normal pregnant (n = 14) women. Here we demonstrate that HLA-DR can be detected in syncytiotrophoblast from a significant proportion of pre-eclampsia but not control placentae. HLA-DR was also observed, by flow cytometry, on STEVs and associated with placental alkaline phosphatase to validate their placental origin. HLA-DR positive syncytiotrophoblast was detected in placental biopsies from pre-eclampsia but not normal control cases, using immunohistochemistry. The HLA may be fetal or maternal origin. In the latter case a possible mechanism of acquisition is trogocytosis.

Comparison of immunological characteristics of mesenchymal stem cells derived from human embryonic stem cells and bone marrow

Mesenchymal stem cell (MSC) has great potential for both regenerative medicine and immunotherapy due to its multipotency and immunomodulatory property. The derivation of MSCs from human tissues involves an invasive procedure and the obtained MSCs often suffer from inconsistent quality. To overcome these issues, the approaches of deriving a highly potent and replenishable population of MSCs from human embryonic stem cells (hESCs) were established. However, few studies compared the immunological characteristics of MSCs derived from hESCs with tissue-derived MSCs or demonstrated differences and the underlying mechanisms. Here, we differentiated H9 hESCs into MSC-like cells (H9-MSCs) through an embryoid body outgrowth method and compared the immunological characteristics of H9-MSCs with bone marrow-derived MSCs (BMSCs). Both sources of derived cells exhibited typical MSC morphologies and surface marker expressions, as well as multipotency to differentiate into osteogenic and adipogenic lineages. A immunological characterization study showed that H9-MSCs and BMSCs had similar immunoprivileged properties without triggering allogeneic lymphocyte proliferation as well as equivalent immunosuppressive effects on T-cell proliferation induced by either cellular or mitogenic stimuli. Flow cytometry analysis revealed a lower expression of human major histocompatability complex class II molecule human lymphocyte antigen (HLA)-DR and a higher expression of coinhibitory molecule B7-H1 in H9-MSCs than in BMSCs. Interferon gamma (IFN-γ) is a proinflammatory cytokine that can induce the expression of HLA class II molecules in many cell types. Our results showed that pretreatment of H9-MSCs and BMSCs with IFN-γ did not change their immunogenicity and immunosuppressive abilities, but increased the difference between H9-MSCs and BMSCs for their expression of HLA-DR. Further detection of expression of molecules involved in IFN-γ signaling pathways suggested that the lower expression of HLA-DR in H9-MSCs could be partially attributed to the lower expression and the less nuclear translocation of its transcriptional factor CIITA. The present study provides evidence that the hESC-derived MSCs share similar immunogenicity and immunosuppressive abilities with BMSCs, but differ in the expression profile of immunological markers and the responsiveness to certain inflammatory cytokines, which suggests that H9-MSCs could be a safe and efficient candidate for MSC treatment in patients with inflammatory disorders.

The placental specific gene, PLAC1, is induced by the Epstein-Barr virus and is expressed in human tumor cells

BACKGROUND

The Epstein-Barr virus (EBV) is a causal agent in a number of malignancies in humans including hematopoietic tumors and non-hematopoietic tumors. Burkitt's lymphoma cell lines containing the Epstein-Barr virus have been shown to form tumors in nude mice while clonal derivatives of such cell lines in which the viral genome has been lost do not (JID 177: 1194-1201, 1998; JV 72: 9150-9156, 1998; JV 68: 6069-6073, 1994). The re-introduction of EBV into these EBV negative BLs reconstitutes the tumor phenotype. Thus, EBV-induced cellular genes play critical role in EBV-related tumors.

METHODS AND RESULTS

In an attempt to identify cellular genes regulated by EBV that may contribute to its tumorigenic properties, we have enforced genome loss in the Burkitt's lymphoma (BL) line, MutuI, by introducing a dominant negative form of the episomal replication factor, EBNA1 and carried out gene array analysis. One of the genes identified by this analysis is PLAC1, a gene originally identified as being expressed exclusively in placental tissue. Real time RT-PCR analysis verified higher expression in EBV positive vs. EBV negative Mutu clones. Analysis of a panel of RNAs from 20 normal tissues demonstrated the highest level of expression in placenta but significant expression was also observed in testis and brain cerebellum. PLAC1 expression was also observed in non-BL tumor cell lines derived from breast, ovary, and prostate. Lastly, expression of PLAC1 was found to be higher in some primary breast tumors compared to normal adjacent tissues.

CONCLUSION

This data suggests that the EBV-induced PLAC1 is a member of the cancer/testis group of tumor antigens.

Maternal thyroid dysfunction affects placental profile of inflammatory mediators and the intrauterine trophoblast migration kinetics

The objective of the present study was to evaluate the gene and immunohistochemical expression of inflammatory mediators involved in the immune activity and the intrauterine trophoblast migration of the placentas in hypothyroid and L-thyroxine (L-T4)-treated rats. A total of 144 adult female rats were divided equally into hypothyroid, l-T4-treated, and euthyroid (control) groups. Hypothyroidism was induced by daily administration of propylthiouracil. Rats were killed at 0, 10, 14, 15, 16, 17, 18, and 19 days of gestation. We evaluated the depth of interstitial and endovascular intrauterine trophoblast invasion and the immunohistochemical expression of interferon γ (INFy), migration inhibitory factor (MIF), and inducible nitric oxide synthase (NOS2 (iNOS)). The gene expression of Toll-like receptor 2 (Tlr2) and Tlr4, Infy, Mif, tumor necrosis factor (Tnf (Tnfα)), Il10, Nos2, matrix metalloproteinase 2 (Mmp2) and Mmp9, and placental leptin was also measured in placental disks by real-time RT-PCR. The data were analyzed using an Student-Newman-Keuls (SNK) test. Hypothyroidism reduced the endovascular and interstitial trophoblast migration, and the expression of TLR4, INFy, MIF, interleukin 10 (IL10), NOS2, MMP2 and MMP9, and placental leptin, while increased the expression of TLR2 (P<0.05). T4-treated rats not only increased the expression of IL10 and NOS2 but also reduced the expression of TNF and MIF at 10 days of gestation (P<0.05). However, at 19 days of gestation, expression of INFy and MIF was increased in T4-treated group (P<0.05). Excess of T4 also increased the gene expression of Mmp2 at 10 days of gestation (P<0.05), but reduced the endovascular trophoblast migration at 18 days of gestation (P<0.05). Hypothyroidism and excess of T4 differentially affect the immune profile and the intrauterine trophoblast migration of the placenta, and these effects are dependent on the gestational period.

Immune response gene profiles in the term placenta depend upon maternal muscle mass

Maternal thinness leads to metabolic challenges in the offspring, but it is unclear whether reduced maternal fat mass or muscle mass drives these metabolic changes. Recently, it has been shown that low maternal muscle mass--as measured by arm muscle area (AMA)--is associated with depressed nutrient transport to the fetus. To determine the role of maternal muscle mass on placental function, we analyzed the gene expression profiles of 30 human placentas over the range of AMA (25.2-90.8 cm(2)) from uncomplicated term pregnancies from the Southampton Women's Survey cohort. Eighteen percent of the ∼60 genes that were highly expressed in less muscular women were related to immune system processes and the interferon-γ (IFNG) signaling pathway in particular. Those transcripts related to the IFNG pathway included IRF1, IFI27, IFI30, and GBP6. Placentas from women with low muscularity are, perhaps, more sensitive to the effects of inflammatory cytokines than those from more muscular women.

Tasmanian devil facial tumor disease: insights into reduced tumor surveillance from an unusual malignancy

Tasmanian devil facial tumor disease (DFTD) is a highly aggressive cancer involving the facial tissues that currently presents a serious extinction risk for the Tasmanian devil population. Although the histogenesis is uncertain, an origin from a neural crest cell-lineage is considered likely. Epidemiological, cytogenetic and immunological data all support the premise that DFTD arose from a single tumor clone from an individual diseased animal, and is being transmitted between individual animals as a tumor "allograft" by biting during social interaction. The spread of this cancer throughout the species is believed to be facilitated by a reduced MHC diversity, possibly as a result of an evolutionary bottleneck. The pathogenesis of DFTD has some similarities with certain human cancers, including donor-recipient tumor transmission, which may complicate organ transplantation, and certain forms of malignancy at the maternal/fetal interface. The natural history and pathology of DFTD, and the data describing this highly unusual tumor biology are discussed.

Immune cells and molecules in pregnancy: friends or foes to the fetus?

Considering allograft rejection as a basic feature of the immune system, the mammalian pregnancy is an immunological paradox where the semi-allogeneic fetus is not rejected. How are the demands of pregnancy solved in the context of maternal immunity? Medawar's original proposal of maternal immune inertness during pregnancy should be revised to active materno-placental tolerance. Multiple mechanisms are involved in peripheral and local tolerance induction that prevents fetal rejection while maintaining competent immune surveillance and protection. The goal of this review is to discuss the major cellular and molecular components of the immune system that control and promote fetal survival.

Immunity, thyroid function and pregnancy: molecular mechanisms

Pregnancy and the postpartum period have a profound effect on autoimmune thyroid disease. Graves disease ameliorates during pregnancy, only to relapse postpartum, whereas postpartum thyroiditis is caused by destructive thyroiditis during the first few months after delivery. The immunology of pregnancy underlies these changes: the mother must maintain tolerance of the fetal semi-allograft while not suppressing her own immune system and exposing herself and the fetus to infection. Nonspecific factors, including hormonal changes, trophoblast expression of key immunomodulatory molecules and a switch to a predominantly T-helper-2-type pattern of cytokines, play some part in the maintenance of transient tolerance to paternal antigens in pregnancy; however, the generation of specific regulatory T (T(REG)) cells is key to this maintenance. T(REG) cells preferentially accumulate in the decidua but may also be present in the mother's circulation and are thus capable of regulating coincidental autoimmune responses through the phenomenon of linked suppression. In turn, this suppression may explain why thyroid autoantibody levels decline during pregnancy, which leads to remission of Graves disease. Postpartum exacerbation of autoimmunity may reflect an imbalance in T(REG) cells, which is caused by the rapid fall in the numbers of these cells after delivery.

The hidden maternal-fetal interface: events involving the lymphoid organs in maternal-fetal tolerance

The genetic disparity between the mother and fetus has long enticed immunologists to search for mechanisms of maternal tolerance to fetal antigens. The study of antigen-specific tolerance in murine and human pregnancy has gained new momentum in recent years through the focus on antigen-presenting cells, uterine lymphatics and fetal antigen-specific maternal T cell responses. In mice, we now know that these responses occur within the secondary lymphoid structures as they can be conveniently tracked through the use of defined, often transgenic fetal antigens and maternal T cell receptors. Although the secondary lymphoid organs are sites of both immunization and tolerization to antigens, the immunological processes that occur in response to fetal antigens during the healthy pregnancy must invariably lead to tolerance. The molecular properties of these maternal-fetal tolerogenic interactions are still being unraveled, and are likely to be greatly influenced by tissue-specific microenvironments and the hormonal milieu of pregnancy. In this article, we discuss the events leading to antigen-specific maternal tolerance, including the trafficking of fetal antigens to secondary lymphoid organs, the properties of the antigen-presenting cells that display them to maternal T lymphocytes, and the nature of the ensuing tolerogenic response. Experimental data generated from human biological specimens as well as murine transgenic models are considered.

Immunobiology of herpes simplex virus and cytomegalovirus infections of the fetus and newborn

Immunologic "immaturity" is often blamed for the increased susceptibility of newborn humans to infection, but the precise mechanisms and details of immunologic development remain somewhat obscure. Herpes simplex virus (HSV) and cytomegalovirus (CMV) are two of the more common severe infectious agents of the fetal and newborn periods. HSV infection in the newborn most commonly occurs after exposure to the virus during delivery, and can lead to a spectrum of clinical disease ranging from isolated skin-eye-mucous membrane infection to severe disseminated multiorgan disease, often including encephalitis. In contrast to HSV, clinically severe CMV infections early in life are usually acquired during the intrauterine period. These infections can result in a range of clinical disease, including hearing loss and neurodevelopmental delay. However, term newborns infected with CMV after delivery are generally asymptomatic, and older children and adults often acquire infection with HSV or CMV with either no or mild clinical symptoms. The reasons for these widely variable clinical presentations are not completely understood, but likely relate to developmental differences in immune responses.This review summarizes recent human and animal studies of the immunologic response of the fetus and newborn to these two infections, in comparison to the responses of older children and adults. The immunologic defense of the newborn against each virus is considered under the broader categories of (i) the placental barrier to infection, (ii) skin and mucosal barriers (including antimicrobial peptides), (iii) innate responses, (iv) humoral responses, and (v) cellular responses. A specific focus is made on recent studies of innate and cellular immunity to HSV and CMV.

Fetomaternal immunotolerance

Implantation of mammalian conceptus in uterine cavity is the result of evolutionary adaptation, through high level of physiological procedures to ensure its success. However the majority of pregnancy losses occur before or during implantation. It is expected that exploring and defining the molecular and physiological road map during the crucial time of implantation will enable us to decode and effectively treat fertility defects. Immunological, hormonal and molecular factors participate in the feto-maternal cross talk during implantation and designate the effectiveness of the process. The atypical expression of major histocompatibility complex and other protein-antigens, such as Fas/FasL and petformin in human trophoblast, the modified function of cellular constituents of the feto-maternal interface, as well as the specific role of some hormones and cytokines, represent substantive parameters of feto-maternal immunotolerance during implantation.

Suppression of lymphocyte proliferation by ovarian cavity fluid from the viviparous fish Neoditrema ransonnetii (Perciformes; Embiotocidae)

As the fetus expresses paternal major histocompatibility complex molecules, viviparous vertebrates require sophisticated mechanisms to modulate maternal immunology to ensure successful pregnancy. We anticipated that ovarian cavity fluid (OCF) is likely to feature significantly in the modulation of ovarian cavity immunology. Consequently, we examined the effects of OCF upon leukocyte function in Neoditrema ransonnetii. OCF did not affect phagocytosis or superoxide production by phagocytes. However, OCF suppressed lymphocyte proliferation induced by ConA almost completely. As OCF contained PGE(2) at high levels during late pregnancy, we also investigated the effect of PGE(2) upon lymphocyte expansion. PGE(2) exhibited negative effects upon lymphocyte mitogenesis in a dose-dependent manner (10-1000 ng/ml). PGE(2) significantly suppressed lymphocyte proliferation when present at levels equivalent to that seen in OCF (30.2 +/- 16.1 approximately 185.4 +/- 107.4 ng/ml). Data indicate that PGE(2) is one of the key modulatory molecules of the maternal immune system ensuring successful pregnancy in this viviparous species.

Histone deacetylases inhibit IFN-gamma-inducible gene expression in mouse trophoblast cells

Trophoblast cells are the first cells to differentiate from the developing mammalian embryo, and they subsequently form the blastocyst-derived component of the placenta. IFN-gamma plays critical roles in activating innate and adaptive immunity, as well as apoptosis. In mice, IFN-gamma is produced in the pregnant uterus, and is essential for formation of the decidual layer of the placenta and remodeling of the uterine vasculature. Responses of mouse trophoblast cells to IFN-gamma appear to be selective, for IFN-gamma activates MHC class I expression and enhances phagocytosis, but fails to activate either MHC class II expression or apoptosis in these cells. To investigate the molecular basis for the selective IFN-gamma responsiveness of mouse trophoblast cells, IFN-gamma-inducible gene expression was examined in the trophoblast cell lines SM9 and M-11, trophoblast stem cells, and trophoblast stem cell-derived giant cells. IFN-gamma-inducible expression of multiple genes, including IFN regulatory factor-1 (IRF-1), was significantly reduced in trophoblast cells compared with fibroblast cells. Decreased IRF-1 mRNA expression in trophoblast cells was due to a reduced rate of IRF-1 transcription relative to fibroblast cells. However, no impairment of STAT-1 tyrosine phosphorylation or DNA-binding capacity was observed in IFN-gamma-treated mouse trophoblast cells. Importantly, histone deacetylase (HDAC) inhibitors significantly enhanced IFN-gamma-inducible gene expression in trophoblast cells, but not fibroblasts. Our collective studies demonstrate that IFN-gamma-inducible gene expression is repressed in mouse trophoblast cells by HDACs. We propose that HDAC-mediated inhibition of IFN-gamma-inducible gene expression in mouse trophoblast cells may contribute to successful pregnancy by preventing activation of IFN-gamma responses that might otherwise facilitate the destruction of the placenta.

The effect of skin allografting on the equine endometrial cup reaction

This research tested the hypothesis that immunological sensitization of mares by skin allografting, followed by the establishment of pregnancy using semen from the skin-graft donor, would give rise to secondary immune responses to the developing horse conceptus, resulting in an earlier demise of the fetally derived endometrial cups. Maiden mares received skin allografts from a stallion homozygous for Major Histocompatibility Complex (MHC) antigens and/or equivalent autografts and were subsequently mated to the skin-graft donor stallion during the next two breeding seasons. Mares that had been immunologically primed to the foreign MHC class I antigens of the skin-graft donor stallion developed strong secondary antibody responses early in their first pregnancies, whereas autografted mares made weak primary antibody responses in their first pregnancies and strong secondary responses in their second pregnancies. In contrast, histological examination of the endometrial cups after surgical pregnancy termination at Day 60 of gestation revealed no discernible differences between allografted and autografted mares, and there were no significant differences in the concentrations and/or duration of secretion of the endometrial cup-specific hormone, equine chorionic gonadotrophin (eCG), between allografted and autografted mares, nor in either group between first and second pregnancies. The vigorous antibody response observed in the pregnant allografted mares supported the first part of our hypothesis, providing evidence of systemic immunological priming. However, there was a lack of an equivalent heightened cellular response to the endometrial cups. These findings provided strong evidence for an asymmetric immune response to the conceptus, characterized by strong humoral immunity and a dampened cellular response.

Regulation of gene expression in mouse trophoblast cells by interferon-gamma

We have previously shown that interferon-gamma (IFN-gamma) activates phagocytosis and induces nitric oxide production in cultured mouse trophoblast cells. In the present study we examined the effect of this cytokine on ectoplacental cone and gene expression in trophoblast cells. Ectoplacental cones were obtained during the postimplantation period on gestational day 7.5 from CD-1 mice and exposed to 100U/mL IFN-gamma. Ectoplacental cone morphology, cell proliferation and death were also determined upon IFN-gamma treatment. Complementary DNA macroarray and semiquantitative RT-PCR were used to analyze gene expression. IFN-gamma treatment did not alter ectoplacental cone morphology, trophoblast cell proliferation or death. However, using gene array technology, we observed that IFN-gamma affected the developing trophoblast, altering the level of mRNA expression, which resulted in upregulation of 35 genes and downregulation of seven others. The upregulation of transcription factors and immune response-associated genes suggests that IFN-gamma is involved in processes beyond immunological homeostasis and plays an important role in placental development and function.

Strong HLA-DR antigen expression on cancer cells relates to better prognosis of colorectal cancer patients: Possible involvement of c-myc suppression by interferon-gamma in situ

Strong HLA-DR antigen expression on cancer cells relates to better prognosis of colorectal cancer patients, although the precise mechanism is controversial. From an immunological point of view, HLA-DR antigen, induced by interferon (IFN)-gamma, is required for tumor-associated antigen recognition by CD4(+) T cells. For instance, as reported previously, the expression of HLA-DR antigen in normal colorectal epithelium immediately adjacent to cancer coincided significantly with the existence of IFN-gamma mRNA in the tissue. From another aspect, IFN-gamma has been revealed to suppress c-myc expression in vivo through a stat1-dependent mechanism, which is important for cell growth, cell cycle and chromosome instability. In the present study, strong HLA-DR-positive expression on cancer cells was significantly related to better prognosis for colorectal cancer patients. High IFN-gamma mRNA expression in situ indicated significantly less activation of c-myc mRNA expression. Further, HLA-DR antigen expression in cancer cells, as well as Dukes stages, was an independent factor for better long-term survival by multivariate analysis. Taken together, IFN-gamma, which induces HLA-DR antigens on the cell surface, also suppresses c-myc expression in situ, and is a possible non-immunological mechanism involved in the better long-term survival of colorectal cancer patients.

Regulation of MHC class II gene expression by the class II transactivator

MHC class II molecules are pivotal for the adaptive immune system, because they guide the development and activation of CD4+ T helper cells. Fulfilling these functions requires that the genes encoding MHC class II molecules are transcribed according to a strict cell-type-specific and quantitatively modulated pattern. This complex gene-expression profile is controlled almost exclusively by a single master regulatory factor, which is known as the class II transactivator. As we discuss here, differential activation of the three independent promoters that drive expression of the gene encoding the class II transactivator ultimately determines the exquisitely regulated pattern of MHC class II gene expression.

Epigenetic control of MHC-II: interplay between CIITA and histone-modifying enzymes

Recent advances have shown the crucial role of histone-modifying enzymes in controlling gene activation and repression. This led to the 'histone code' hypothesis, which proposes that combinations of histone modifications work in concert to affect specific gene expression. Mounting evidence suggests that the class II transactivator modulates promoter accessibility by coordinating the recruitment of chromatin modifiers in a time-dependent fashion. MHC-II expression is exquisitely controlled by these highly specific, coordinated and dynamic interactions at the promoter.