Fetal Allograft Research Articles

T‐cell Tolerance to the Developing Equine Conceptus

One of the most intriguing and dramatic examples of immunological tolerance is displayed by the mammalian foetal-placental unit, which thrives as a semi-allograft in the mother's uterus during pregnancy. The success of the so-called foetal allograft stands in stark contrast to the failure of most tissue and organ grafts to survive without genetic matching of donor and recipient or drastic immunosuppression of the recipient's immune system. Experiments conducted over the past 60 years have revealed multiple mechanisms that enable the conceptus to avoid immunological detection or destruction. Many of these mechanisms are directed towards evading immune-mediated damage by maternal T lymphocytes, and they can be grouped into three classes: (i) downregulation of major histocompatibility complex (MHC) gene expression in placental trophoblast cells; (ii) local and systemic alterations in maternal immune reactivity; and (iii) innate defence mechanisms of the trophoblast cells that comprise the barrier between foetal and maternal tissues. The redundancy in these protective mechanisms helps ensure the transmission of life from generation to generation and provides a rich field of study of ways in which functional immunological tolerance can be manifest. The variation in placental forms and function among mammalian species present opportunities to discover and understand novel tolerogenic mechanisms that may have broad application in biology, medicine and animal husbandry. This review focuses on the evidence obtained from studies of pregnancy in the mare that support the case for selective T-cell tolerance to the mammalian conceptus.

Trophoblast debris modulates the expression of immune proteins in macrophages: a key to maternal tolerance of the fetal allograft?

Interactions between maternal immune cells and the placenta are of substantial interest since diseases of pregnancy, such as recurrent miscarriage, villitis of unknown etiology and preeclampsia may arise due to inadequate adaptation of the maternal immune system. During normal pregnancy trophoblast debris is shed from the placenta into the maternal blood in large quantities. This trophoblast debris is then rapidly cleared from the maternal circulation. In this study, we exposed trophoblast debris generated from an in vitro placental explant model to peripheral blood-derived macrophages and quantified a variety of molecules that are important in immune responses by ELISA or flow cytometry. Phagocytosis of trophoblast debris resulted in reduced cell-surface expression of MHC-II molecules, the costimulatory molecules (CD80, CD86, CD40 and B7H3), monocyte chemoattractant protein-1 (MCP-1), inter-cellular adhesion molecule 1 (ICAM-1) and IL-8 receptors in macrophages while the expression of programmed death-1 ligand 1 (PD-L1) was upregulated. In addition, phagocytosis of trophoblast debris induced the secretion of the anti-inflammatory cytokines IL-10, IL6 and IL1Ra and decreased the secretion of pro-inflammatory cytokines IL-1β, IL12p70 and IL-8 by macrophages. Phagocytosis of trophoblast debris also increased macrophage expression of the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO). We have shown that phagocytosis of trophoblast debris from normal placentae alters the phenotype of macrophages such that they are likely to deviate maternal immune responses towards tolerance and away from inflammation. This may be one of the mechanisms that allow the human fetal allograft to survive in direct contact with the maternal immune system.

Calcitriol inhibits interleukin-10 expression in cultured human trophoblasts under normal and inflammatory conditions

Preeclampsia is associated with systemic inflammation and increased expression of placental Th1-cytokines. IL-10 and calcitriol inhibit proinflammatory cytokines expression in human placenta helping to fetal allograft toleration. Regulation of placental IL-10 by calcitriol and Th-1 cytokines has not yet been fully elucidated. Since it is believed that calcitriol promotes a shift from a Th1- to a Th2 profile, we hypothesized that it would stimulate IL-10 in a normal and an inflammatory scenario to conjointly restrain inflammation. Therefore, we investigated calcitriol effects upon IL-10 expression in cultured human trophoblasts obtained from normal (NT) and preeclamptic (PE) pregnancies. Similar studies in the presence of TNF-α (as an inflammatory stressor) were also performed. Calcitriol dose-dependently inhibited IL-10 expression in NT, PE and TNF-α-challenged trophoblasts (P<0.05). This effect was prevented by a vitamin D receptor (VDR) antagonist. IL-10 expression was significantly stimulated by TNF-α and IL-1β, inhibited by IFN-γ and was not affected by IL-6. Finally, calcitriol inhibited TNF-α and IL-1β stimulation upon IL-10. In summary, in cultured human trophoblasts, calcitriol down-regulates IL-10 expression under normal as well as under natural and experimental inflammatory conditions. This effect is mediated by the VDR and might involve direct inhibition of TNF-α. In view of these and previous results it seems that in placenta calcitriol suppresses both Th1- and Th2 cytokines while undertakes the anti-inflammatory effects of IL-10 by itself, since both factors exert this task redundantly. The regulation of IL-10 by IFN-γ suggests that this cytokine could be a viable candidate to explain low IL-10 levels in preeclampsia.

Indoleamine 2,3-Dioxygenase Expression in Human Cancers: Clinical and Immunologic Perspectives

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-catabolizing enzyme with immune-regulating activities in many contexts, such as fetal protection, allograft protection, and cancer progression. Clinical trials are currently evaluating IDO inhibition with 1-methyltryptophan in cancer immunotherapy. However, the exact role of tryptophan catabolism by IDO in human cancers remains poorly understood. Here, we review several studies that correlate IDO expression in human cancer samples and tumor-draining lymph nodes, with relevant clinical or immunologic parameters. IDO expression in various histologic cancer types seems to decrease tumor infiltration of immune cells and to increase the proportion of regulatory T lymphocytes in the infiltrate. The impact of IDO on different immune cell infiltration leads to the conclusion that IDO negatively regulates the recruitment of antitumor immune cells. In addition, increased IDO expression correlates with diverse tumor progression parameters and shorter patient survival. In summary, in the vast majority of the reported studies, IDO expression is correlated with a less favorable prognosis. As we may see results from the first clinical trials with 1-methyltryptophan in years to come, this review brings together IDO studies from human studies and aims to help appreciate outcomes from current and future trials. Consequently, IDO inhibition seems a promising approach for cancer immunotherapy.

Role of Minimal Access Surgery in Gestational Trophoblastic Disease

Gestational trophoblastic diseases (GTD) comprise a spectrum of tumor and tumor-like conditions that originate from the fetal chorion.Trophoblastic tumors are fetal allograft in maternal tissues and present unique biological, immunological and pathological problems.Suction and evacuation followed by serial estimation of serum hCG and chemotherapy are the mainstay of treatment. Hysterectomy isthe treatment of choice for patients with placental site trophoblastic tumors and also for persistent chemotherapy resistant uterinedisease. This treatment may be unacceptable to the woman who wishes to retain her fertility. With quality of life issues becoming moreimportant in medicine, therapies which preserve fertility, without compromising adequate treatment of the disease, should receiveserious consideration. Laparoscopic hysterectomy and robotic hysterectomy are good options for women who are considered forsurgery. Hysteroscopy also has a role in localizing and obtaining uterine (endometrial/myometrial) tissues for histopathological studies.It also helps in differentiating the diagnosis of gestational trophoblastic neoplasia from other conditions of raised serum hCG like ectopicpregnancy (cornual), incomplete abortion and nongestational trophoblastic tumors.Aim of study: The aim of this study is to evaluate the role of minimal access surgical procedures like laparoscopy, hysteroscopy androbotic surgery in the management of gestational trophoblastic tumors.Methodology: (1) Materials: The study was carried out through a literature search using the information technology installations of theWorld Laparoscopy Hospital, Gurgaon, NCR, Delhi. (2) Time: The study was carried out during a period of 2 weeks between July 12th,2011 and July 26th, 2011.Data collection: All the publications used in the current study was accessed from the electronic (virtual) library using the followingsearch engines: Google, SpringerLink, PubMed, Highwire press, Medline.Abbreviations: (1) GTD: Gestational trophoblastic disease, (2) GTT: Gestational trophoblastic tumor, (3) GTN: Gestational trophoblasticneoplasia, (4) PSTT: Placental site trophoblastic tumor.

Placental C4d and anti-HLA antibodies in patients with recurrent miscarriage of unknown etiology: humoral rejection of the fetal allograft?

Placental C4d and anti-HLA antibodies in patients with recurrent miscarriage of unknown etiology: humoral rejection of the fetal allograft?

Medawar Redux – An Overview on the Use of Farm Animal Models to Elucidate Principles of Reproductive Immunology

Farm animals have been important models for the development of reproductive immunology. Two of the major concepts underpinning reproductive immunology, the idea of the fetal allograft and progesterone's role in regulation of uterine immunity, were developed using the bovine as a model. This volume of the American Journal of Reproductive Immunology is composed of review articles that highlight the continued relevance of farm animals as models for research in mammalian biology. It is important that a diverse array of genotypes are used to elucidate biological principles relevant to mammalian biology and human health because the nature of mammalian evolution has resulted in a situation where the genome of the most commonly used animal model, the laboratory mouse, is less similar to the human than other species like the cow. Moreover, the evolution of placental function has been accompanied by formation of new genes during recent evolution so that orthologs do not exist in any but closely related species. Given the infrastructure needs to study farm animal species, optimal utilization of these animals as models for biomedical research will require significant increases in funding to reverse a historical erosion of resources devoted to animal agricultural research.

Evolution and Function of the Uterine Serpins (SERPINA14)

Uterine serpins (recently designated as SERPINA14) are hormonally induced proteins secreted in large quantities by the endometrial epithelium during pregnancy. The SERPINA14 proteins belong to the serine proteinase inhibitor (serpin) superfamily, but their apparent lack of inhibitory activity toward serine proteinases suggests that these proteins evolved a different function from the anti-proteinase activity typically found in most members of the serpin superfamily. The gene is present in a limited group of mammals in the Laurasiatheria superorder (ruminants, horses, pigs, dolphins and some carnivores) while being absent in primates, rodents, lagomorphs and marsupials. Thus, the gene is likely to have evolved by gene duplication after divergence of Laurasiatheria and to play an important role in pregnancy. That role may vary between species. In sheep, SERPINA14 probably serves an immunoregulatory role to prevent rejection of the fetal allograft. It is inhibitory to lymphocyte proliferation and natural killer cell function. In the pig, SERPINA14 is involved in iron transport to the fetus by binding to and stabilizing the iron-binding protein uteroferrin. It is possible that SERPINA14 has undergone divergence in function since the original emergence of the gene in a common ancestor of species possessing SERPINA14.

Placental exosome-mediated immune protection of the fetus: feeling groovy in a cloud of exosomes

Exosomes are nanosized membrane-bound microvesicles that originate from the endosomal compartment and convey cell–cell contact ‘by proxy’, transporting signals/packages of information between donor and recipient cells locally and/or at a distance. Exosomes are produced by a variety of immune, epithelial and tumor cells. Upon contact, exosomes transfer molecules that can render new properties and/or reprogram the recipient cells. Recently, it was discovered that the syncytiotrophoblast of human placenta continuously and constitutively secretes exosomes throughout pregnancy. These exosomes, delivered directly in the maternal blood surrounding the chorionic villi of the placenta, are immunosuppressive and pluripotent carrying proteins, mRNA and miRNA that can influence a number of biologic mechanisms and promote the fetal allograft survival. The current knowledge regarding placental exosomes and their role in pregnancy is summarized and discussed in this article.

Natural killer cell analysis for reproductive failure: madness, methods and more!

Our understanding of the immunology of pregnancy has been dominated by the fetal allograft model and by changes in the maternal-specific immune system. Here, Gavin Sacks and colleagues draw attention to substantial and contrasting changes in the maternal innate system and hypothesize that its function and that of monocytes in particular, has a central role in the maternal–fetal relationship.

The Endometrial Response to Chorionic Gonadotropin Is Blunted in a Baboon Model of Endometriosis

Endometriosis-associated infertility has a multifactorial etiology. We tested the hypothesis that the endometrial response to the early embryonic signal, human chorionic gonadotropin (hCG), alters over time in a nonhuman primate model of endometriosis. Animals with experimental or spontaneous endometriosis were treated with hCG (30 IU/d), from d 6 after ovulation for 5 d, via an oviductal cannula. Microarray analysis of endometrial transcripts from baboons treated with hCG at 3 and 6 months of disease (n=6) identified 22 and 165 genes, respectively, whose levels differed more than 2-fold compared with disease-free (DF) animals treated with hCG (P<0.01). Quantitative RT-PCR confirmed abnormal responses of known hCG-regulated genes. APOA1, SFRP4, and PAPPA, which are normally down-regulated by hCG were up-regulated by hCG in animals with endometriosis. In contrast, the ability of hCG to induce SERPINA3 was lost. Immunohistochemistry demonstrated dysregulation of C3 and superoxide dismutase 2 proteins. We demonstrate that this abnormal response to hCG persists for up to 15 months after disease induction and that the nature of the abnormal response changes as the disease progresses. Immunohistochemistry showed that this aberrant gene expression was not a consequence of altered LH/choriogonadotropin receptor distribution in the endometrium of animals with endometriosis. We have shown that endometriosis induces complex changes in the response of eutopic endometrium to hCG, which may prevent the acquisition of the full endometrial molecular repertoire necessary for decidualization and tolerance of the fetal allograft. This may in part explain endometriosis-associated implantation failure.

The presence of HLA-antibodies in recurrent miscarriage patients is associated with a reduced chance of a live birth

Anti-paternal HLA-antibodies are considered a harmless phenomenon during most pregnancies, whereas their role in recurrent miscarriage (RM) patients is disputed. In contrast to primary RM, patients with secondary RM have carried a fetus to term pregnancy prior to a series of miscarriages, which increases the chance that allogeneic fetal cells appear in the maternal circulation. This study investigates the frequency of HLA-antibodies in secondary RM, primary RM patients and parous controls and analyzes whether the presence of HLA-antibodies in early pregnancy is associated with pregnancy outcome. Sera from women with secondary RM (n=56), primary RM (n=13) and parous controls (n=24) were tested for HLA-antibodies using an ELISA assay and complement dependent cytotoxicity. Samples were taken at gestational week 4-5 in 62 (90%) of the patients. HLA-antibodies were significantly more frequent in secondary RM patients with a boy prior to the miscarriages (62%) compared to secondary RM patients with a firstborn girl (29%, p=0.03), primary RM patients (23%, p=0.02) and parous controls (25%, p=0.005). Forty-one percent of HLA-antibody positive pregnant RM patients had a live birth compared to 76% of HLA-antibody negative RM patients, p=0.006 (adjusted OR: 0.22 (0.07-0.68), p=0.008). In conclusion, HLA-antibodies are significantly more frequent in secondary RM patients with a firstborn boy than in other RM patients and controls. The presence of these antibodies in early pregnancy is associated with a reduced chance of a live birth. Further exploring this association may increase our understanding of maternal acceptance of the fetal allograft.

REVIEW ARTICLE: The Role of Placental Exosomes in Reproduction

Cell communication comprises cell-cell contact, soluble mediators and intercellular nanotubes. There is, however, another cell-cell communication by released membrane-bound microvesicles that convey cell-cell contact 'by proxy' transporting signals/packages of information from donor to recipient cells locally and/or at a distance. The nanosized exosomes comprise a specialized type of microvesicles generated within multivesicular bodies (MVB) and released upon MVB fusion with the plasma membrane. Exosomes are produced by a variety of immune, epithelial and tumor cells. Upon contact, exosomes transfer molecules that can render new properties and/or reprogram their recipient cells. Recently, it was discovered that the syncytiotrophoblast constitutively and throughout the pregnancy secretes exosomes. The placenta-derived exosomes are immunosuppressive and carry proteins and RNA molecules that in a redundant way influence a number of mechanisms and promote the fetal allograft survival. In this review, we summarize the current knowledge on the nature of placenta-derived exosomes and discuss their role in pregnancy.

REVIEW ARTICLE: Interleukin‐10: A Multi‐Faceted Agent of Pregnancy

Citation Thaxton JE, Sharma S. Interleukin‐10: a multi‐faceted agent of pregnancy. Am J Reprod Immunol 2010It is widely accepted that pregnancy constitutes a unique developmental event. Unprecedented intrauterine actions of angiogenesis, immunity, and neuroendocrine regulation are juxtaposed to mechanisms of senescence that enable fetal growth and protection. The suppressive and regulatory factors that facilitate healthy pregnancy are under investigation. In non‐pregnant systems of infection and inflammation, the cytokine interleukin‐10 (IL‐10) has been widely investigated because of its potential as a key immunosuppressant in response to a multitude of inflammatory events. In the context of pregnancy, IL‐10 levels increase markedly in women during early pregnancy and remain elevated well into the third trimester immediately prior to onset of labor. The role of IL‐10 during pregnancy as a suppressor of active maternal immunity to allow acceptance of the fetal allograft has been a point of study. Moreover, secretion of IL‐10 by a diverse set of maternal and fetal cells has proven to aid in the orchestration of normal processes of pregnancy. Interestingly, some of the more profound findings regarding the actions of IL‐10 during pregnancy have manifested from research that focuses on aberrant pregnancy outcomes as a result of inflammation, hormonal imbalances, or gene–environment interactions. This review focuses on the role of IL‐10 as a facilitator of successful pregnancy both as an immune suppressive agent and a mediator of cross talk between the placenta and the decidua. Importantly, we discuss investigations on adverse pregnancy conditions to further elucidate the multifarious role of IL‐10 at the maternal–fetal interface.

T cell tolerance towards the fetal allograft

The conceptus is considered a semi-allograft because of the presence of paternal HLA-C molecules. These alloantigens can be processed by maternal antigen presenting cells, which present them to specific maternal CD4+ T cells. After activation, the maternal CD4+ T cells can become effector decidual CD4+ T cells, which are able to release various cytokines. Th1-type cytokines (IFNgamma) that promote allograft rejection may compromise pregnancy, whereas the Th2-type cytokines (IL-4, IL-10) that inhibit Th1 responses, promote allograft tolerance and therefore may improve fetal survival. A collaborative interaction between the decidual natural regulatory T cells, CD4+ CD25+ Foxp3 T cells and NKT cells in preventing fetal allograft rejection is suggested.

ORIGINAL ARTICLE: Impact of Female Sex Hormones on the Maturation and Function of Human Dendritic Cells

Problem During pregnancy, the immune and the endocrine system cooperate to ensure that the fetal allograft develops without eliciting a maternal immune response. This is presumably in part achieved by dendritic cells (DCs) that play a dominant role in maintaining peripheral tolerance. In this study, we investigated whether female sex hormones, such as human chorionic gonadotropin (hCG), progesterone (Prog), and estradiol (E2), which are highly elevated during pregnancy, induce the differentiation of DCs into a tolerance‐inducing phenotype.Methods/Results Immature DCs were generated from blood‐derived monocytes and differentiated in the presence of hCG, Prog, E2, or Dexamethasone (Dex) as a control. Unlike Dex, female sex hormones did not prevent the upregulation of surface markers characteristic for mature DCs, such as CD40, CD83, and CD86, except for hCG, which inhibited HLA‐DR expression. Similarly, hCG, Prog, and E2 had any impact on neither the rearrangement of the F‐actin cytoskeleton nor the enhanced chemokine secretion following DC maturation, both of which were strongly altered by Dex. Nevertheless, the T‐cell stimulatory capacity of DCs was significantly reduced after hCG and E2 exposure.Conclusion Our findings suggest that the female sex hormones hCG and E2 inhibit the T‐cell stimulatory capacity of DCs, which may help in preventing an allogenic T‐cell response against the embryo.

Dendritic cell entrapment within the pregnant uterus inhibits immune surveillance of the maternal/fetal interface in mice

Embryo implantation induces formation of the decidua, a stromal cell-derived structure that encases the fetus and placenta. Using the mouse as a model organism, we have found that this tissue reaction prevents DCs stationed at the maternal/fetal interface from migrating to the lymphatic vessels of the uterus and thus reaching the draining lymph nodes. Strikingly, decidual DCs remained immobile even after being stimulated with LPS and exhibiting responsiveness to CCL21, the chemokine that drives DC entry into lymphatic vessels. An analysis of maternal T cell reactivity toward a surrogate fetal/placental antigen furthermore revealed that regional T cell responses toward the fetus and placenta were driven by passive antigen transport and thus the tolerogenic mode of antigen presentation that predominates when there is negligible input from tissue-resident DCs. Indeed, the lack of involvement of tissue-resident DCs in the T cell response to the fetal allograft starkly contrasts with their prominent role in organ transplant rejection. Our results suggest that DC entrapment within the decidua minimizes immunogenic T cell exposure to fetal/placental antigens and raise the possibility that impaired development or function of the human decidua, which unlike that of the mouse contains lymphatic vessels, might lead to pathological T cell activation during pregnancy.

Reply: Influence of activating and inhibiting killer immunoglobulin-like receptors on predisposition to recurrent miscarriages

Understanding of the immune events and mechanisms occurring at the feto-maternal interface is likely to help in understanding the ability of the fetus to survive within the maternal body. Evidence supporting extensive roles of natural killer cells during pregnancy gives rise to a possibility that these NK cells can be mis-regulated and involved in fetal allograft rejection. Killer immunoglobulin-like receptors (KIR) play an important role in regulating the NK cell activity through their activating and inhibiting isoforms. Since there exists a considerable, genetically determined variation in the repertoire of KIR receptors between different individuals, a particular maternal KIR repertoire may predispose to recurrent miscarriages (RMs).Gene-specific PCR amplification (PCR-SSP) was used to determine the individual KIR genotypes in women experiencing RM and controls.A higher prevalence of activating KIR genes was seen in patients than in controls. Among women experiencing RM, the BB genotypes were more prevalent (P < 0.0001, OR = 4.4, 95% CI = 2.89-6.69) compared with controls.Our results indicate that the balance between inhibitory and activating receptor-mediated signals present in natural killer cells is inclined toward a more activating state that may contribute to pregnancy loss.

Influence of activating and inhibitory killer immunoglobulin-like receptors on predisposition to recurrent miscarriages

Understanding of the immune events and mechanisms occurring at the feto-maternal interface is likely to help in understanding the ability of the fetus to survive within the maternal body. Evidence supporting extensive roles of natural killer cells during pregnancy gives rise to a possibility that these NK cells can be mis-regulated and involved in fetal allograft rejection. Killer immunoglobulin-like receptors (KIR) play an important role in regulating the NK cell activity through their activating and inhibiting isoforms. Since there exists a considerable, genetically determined variation in the repertoire of KIR receptors between different individuals, a particular maternal KIR repertoire may predispose to recurrent miscarriages (RMs). Gene-specific PCR amplification (PCR-SSP) was used to determine the individual KIR genotypes in women experiencing RM and controls. A higher prevalence of activating KIR genes was seen in patients than in controls. Among women experiencing RM, the BB genotypes were more prevalent (P < 0.0001, OR = 4.4, 95% CI = 2.89-6.69) compared with controls. Our results indicate that the balance between inhibitory and activating receptor-mediated signals present in natural killer cells is inclined toward a more activating state that may contribute to pregnancy loss.

You are what you eat and what you practice

You are what you eat and what you practice