Functional characteristics of human trophoblast interferons

Understanding the Immune System in Fetal Protection and Maternal Infections during Pregnancy

The fetal-maternal immune system determines the fate of pregnancy. The trophoblast cells not only give an active response against external stimuli but are also involved in secreting most of the cytokines. These cells have an essential function in fetal acceptance or fetal rejection. Other immune cells also play a pivotal role in carrying out a successful pregnancy. The disruption in this mechanism may lead to harmful effects on pregnancy. The placenta serves as an immune barrier in fetus protection against invading pathogens. Once the infections prevail, they may localize in placental and fetal tissues, and the presence of inflammation due to cytokines may have detrimental effects on pregnancy. Moreover, some pathogens are responsible for congenital fetal anomalies and affect almost all organs of the developing fetus. This review article is designed to address the bacterial and viral infections that threaten pregnancy and their possible outcomes. Moreover, training of the fetal immune system against the exposure of infections and the role of CD49a + NK cells in embryonic development will also be highlighted.

The unique immunological and microbial aspects of pregnancy

The comparison of the immunological state of pregnancy to an immunosuppressed host-graft model continues to lead research and clinical practice to ill-defined approaches. This Review discusses recent evidence that supports the idea that immunological responses at the receptive maternal-fetal interface are not simply suppressed but are instead highly dynamic. We discuss the crucial role of trophoblast cells in shaping not only the way in which immune cells respond to the invading blastocyst but also how they collectively react to external stimuli. We also discuss the role of the microbiota in promoting a tolerogenic maternal immune system and highlight how subclinical viral infections can disrupt this status quo, leading to pregnancy complications.

Breast cancer characteristics are modified by first trimester human placenta: in vitro co-culture study

BACKGROUND

Pregnant women with breast cancer present with a more advanced disease compared with non-pregnant women. Nevertheless, breast cancer metastasis to the placenta is rare. Trophoblast/tumor implantations share the same biochemical mediators, while only the first is stringently controlled. We hypothesized that the same mechanisms that affect/restrain placental implantation may inhibit metastatic growth in the placenta. We aimed to analyze the effects of human placenta on breast cancer cells.

METHODS

First trimester human placental explants were co-cultured with MCF-7/T47D-eGFP tagged cells. Following culture, placenta/cancer cells/both were fixed, paraffin embedded and sliced for immunohistochemical analysis or sorted by their eGFP expression for future analysis. The tested parameters were: proliferation (immunohistochemistry)/cell cycle (FACS), apoptosis (immunohistochemistry/FACS), cell count/adhesion/distribution around the placenta (cell sorter, visual observation and counting), matrix metalloproteinase activity (zymogram) and estrogen receptor (ER) expression (western blotting, immunohistochemistry).

RESULTS

Reduced breast cancer cell numbers (45%↓, 48%↓ for MCF-7/T47D, respectively, P < 0.05) were observed near the placenta. The placenta elevated MCF-7 sub-G1 phase and modestly elevated apoptosis (3-17%↑ for T47D/MCF-7, respectively, P < 0.05). Our findings demonstrate breast cancer cell migration from the placenta as: (i) T47D/MCF-7 cells changed their morphology to that of motile cells; (ii) elevated MMPs activity was found in the co-culture; (iii) placental soluble factors detached breast cancer cells; and (4) the placenta reduced MCF-7/T47D cells' ER expression (a characteristic of motile cells).

CONCLUSIONS

MCF-7/T47D cells are eliminated from the placental surroundings. Analyzing the causes of these phenomena may suggest biological pathways for this event and raise new therapeutic targets.

Comparative aspects of implantation

Uterine receptivity to implantation of blastocysts in mammals includes hatching from zona pellucida, precontact with uterine luminal (LE) and superficial glandular (sGE) epithelia and orientation of blastocyst, apposition between trophectoderm and uterine LE and sGE, adhesion of trophectoderm to uterine LE/sGE, and, in some species, limited or extensive invasion into the endometrial stroma and induction of decidualization of stromal cells. These peri-implantation events are prerequisites for pregnancy recognition signaling, implantation, and placentation required for fetal-placental growth and development through the remainder of pregnancy. Although there is a range of strategies for implantation in mammals, a common feature is the requirement for progesterone (P(4)) to downregulate expression of its receptors in uterine epithelia and P(4) prior to implantation events. P(4) then mediates its effects via growth factors expressed by stromal cells in most species; however, uterine luminal epithelium may express a growth factor in response to P(4) and/or estrogens in species with a true epitheliochorial placenta. There is also compelling evidence that uterine receptivity to implantation involves temporal and cell-specific expression of interferon (IFN)-stimulated genes that may be induced directly by an IFN or induced by P(4) and stimulated by an IFN. These genes have many roles including nutrient transport, cellular remodeling, angiogenesis and relaxation of vascular tissues, cell proliferation and migration, establishment of an antiviral state, and protection of conceptus tissues from challenges by the maternal immune cells.

Endogenous interferon-alpha level is increased in hepatitis C virus (HCV)-positive pregnant women

BACKGROUND

Mother-to-child transmission of hepatitis C virus (HCV) has been reported in around 5% of cases, and is much more likely to occur in case of coinfection with HIV. However, other cofactors influencing the vertical transmission are still debated.

AIM

To assess the serum concentration of endogenous interferon (IFN) during pregnancy, and its eventual role on the vertical transmission of HCV.

METHODS

Forty-seven HCV-infected pregnant women, and 3 control groups: (1) 75 HCV-negative pregnant women; (2) 29 HCV-positive nonpregnant women; (3) 29 HCV-negative nonpregnant women entered into the study. Endogenous IFN was assayed by enzyme-linked immunosorbent assay. The following parameters were also analyzed: viral load, HIV infection, risk factors for acquiring HCV, parity, gestational age, mode and course of delivery.

RESULTS

Vertical transmission of HCV was observed in 2 cases (4.3%). Plasma levels of IFN were significantly higher in HCV-positive pregnant women compared with either HCV-positive and HCV-negative nonpregnant women. The 2 mothers who transmitted the infection had IFN levels within the same range as the women who did not transmit the infection.

CONCLUSIONS

In HCV-positive pregnant women, there is an increased production of endogenous IFN-alpha. Further studies are warranted for clarifying the mechanisms of this cytokine in the prevention of HCV transmission.

Interferons and the maternal-conceptus dialog in mammals

Two-way communication between the conceptus and the mother during early pregnancy is essential if the pregnancy is to survive. In this review, our primary focus is on biochemical communication between the conceptus and mother in the ruminant ungulate species. We emphasize, in particular, the role played by interferon-tau (IFNT) in triggering maternal responses in cattle and sheep and how maternal factors intervene to up-regulate IFNT gene (IFNT) expression in trophoblast. However, we also consider the possibility that different signaling cytokines or the physical presence of trophoblast may induce a partial IFN response in endometrium of those species where there is no evidence for large scale trophoblast IFN production. Conceivably, disparate signaling mechanisms trigger common downstream events necessary to secure a successful pregnancy.

PL74, a novel member of the transforming growth factor-beta superfamily, is overexpressed in preeclampsia and causes apoptosis in trophoblast cells

PL74, a novel member of the TGFbeta superfamily that has highest expression in placenta, is a multifunctional peptide that can induce differentiation, inhibit inflammatory stimulation of TNFalpha, and execute apoptosis after p53 overexpression and cytotoxic injury. To study its expression and function in placenta and preeclampsia, we first determined mRNA expression in nine normal and 10 preeclamptic placentas. PL74 mRNA was overexpressed by 57.3% in preeclampsia. Transfection of PL74 into term cytotrophoblasts resulted in increased apoptosis by terminal uridine deoxynucleotidyl nick end labeling labeling (control, 2.8 +/- 0.5%; PL74, 19.1 +/- 0.2%; P < 0.005). Addition of PL74 protein to HTR8/SVneo extravillous cytotrophoblast cells showed a dose-response (0-100 ng/ml) inhibition of [3H]thymidine uptake and increase in apoptosis shown by terminal uridine deoxynucleotidyl nick end labeling and histone-associated DNA fragment ELISA (control, 0.11 +/- 0.01 absorbance units; PL74, 0.21 +/- 0.01; P < 0.01). PL74 did not alter cytotrophoblast invasion using a Matrigel in vitro invasion assay. Cytokine regulation of PL74 mRNA expression in term cytotrophoblasts showed that epidermal growth factor and IFNgamma increased PL74 expression, but TGFbeta and TNFalpha had no effect. Transfection of antisense PL74 into term cytotrophoblast cells resulted in an inhibition of spontaneous differentiation at 2 and 24 h of culture (control vector, 30.8 +/- 3.1% and 26.4 +/- 1.2%; antisense PL74, 17.6 +/- 1.8%and 12.6 +/- 1.4% syncytial units, at 2 and 24 h respectively; P < 0.01). We conclude that PL74 is overexpressed in preeclampsia and may thus promote apoptosis of cytotrophoblasts at the expense of differentiation. PL74 secretion is induced by IFNgamma and may play a role in abnormal placental responses in preeclampsia.

Ex vivo cytokine responses against parvovirus B19 antigens in previously infected pregnant women

Parvovirus B19 infection is a significant cause of fetal death. The aim of this study was to investigate the role of maternal immune status in modulating susceptibility to fetal B19 infection. Peripheral blood was obtained from pregnant women (n = 199) with no clinical evidence of recent B19 infection. Evaluation of ex vivo T cell responses from 149/199 individuals showed significantly higher interferon-gamma levels for seropositive individuals following VP1 (268 +/- 36 versus 103 +/- 19 pg/ml; P = 0.003) and VP2 (242 +/- 42 versus 91 +/- 16 pg/ml; P = 0.01) antigen stimulation. Significantly higher levels of interleukin-2 were also observed in seropositive individuals following both VP1 (P = 0.0003) and VP2 (P = 0.0005) stimulation. The observed Th1 cellular response is lower than that documented previously for non-pregnant individuals and strongly suggests that diminution of the maternal anti-viral immune response may increase susceptibility to fetal B19 infection.

Gene expression of double-stranded RNA-dependent protein kinase in the human endometrium and decidua

To clarify the biological significance of double-stranded RNA-dependent protein kinase (PKR), an interferon (INF)-inducible substance, we investigated (1) PKR gene expression and the (2) effect of IFN-gamma on PKR gene expression in human endometrium. By Northern blot analysis, PKR mRNA was detected as a 2.5 kb band in human endometrium throughout the menstrual cycle and decidua in early pregnancy. The addition of IFN-gamma to culture medium increased the PKR mRNA level in a dose-dependent manner in cultured endometrial stromal cells. These results suggest that IFN-gamma, which is reported to have an inhibitory effect on cell proliferation, plays an important role in human endometrial function by mediating PKR gene expression.

First-trimester human chorionic villi express both immunoregulatory and inflammatory cytokines: a role for interleukin-10 in regulating the cytokine network of pregnancy

PROBLEM

T-helper 2 (TH2)-type cytokines [i.e., interleukin (IL)-6, IL-10, and IL-13] and transforming growth factor (TGF)-beta are expressed by the murine decidua and/or placenta and are likely to suppress inflammatory cytokine [i.e., IL-2, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, IL-1 alpha, and IL-1 beta] production at the maternal-fetal interface. In addition, class I IFNs may protect the fetus from immunologic rejection and viral infections. This study examines the expression of inflammatory/immunoregulatory cytokines and IL-10 production by first-trimester chorionic villi.

METHOD OF STUDY

Gestational tissues (n = 5) were obtained following elective terminations performed between 7 and 9 weeks of gestation. Chorionic villous tissues were separated from fetal membranes and decidua, and total RNA was extracted. Cytokine expression was assessed by a reverse transcriptase-polymerase chain reaction technique. Chorionic villi (n = 9; 6-12 weeks gestation) were maintained in organ culture, and human chorionic gonadotropin (hCG) and IL-10 levels were determined by immunoradiometric and enzyme-linked immunosorbent assays, respectively.

RESULTS

IFN-gamma and IL-2 were generally not expressed by first-trimester chorionic villi. Low to moderate levels of expression were noted for IL-1 alpha, IL-1 beta, and TNF-alpha. High levels of mRNA were noted for IFN-alpha and IFN-beta, but IFN-tau was not expressed. In all tissues, TGF-beta 1 and IL-13 were either weakly expressed or not expressed. In contrast, moderate to high levels of IL-6 and IL-10 mRNA were detected in each chorionic villous sample. In chorionic villous explants obtained at 6-11 weeks gestation production of hCG and IL-10 was greatest during the first 24 hr ([hCG] = 6961 +/- 815 mIU/mL, [IL-10] = 92 +/- 11 pg/mL) and then declined through 72 hr.

CONCLUSIONS

TH1-type cytokines (IL-2, IFN-gamma) are not expressed by first-trimester chorionic villous tissues: This is possibly due to local production of IL-10. In contrast, macrophage-associated cytokines (IL-1 beta and TNF-alpha) are expressed and their regulation may be critical for fetal survival. Finally, class 1 IFNs expressed by early chorionic tissues may protect the fetus from maternal rejection and viral transmission.

Cytokine expression by first-trimester human chorionic villi

PROBLEM

Communication at the human maternal-fetal interface occurs by an intricate cytokine network. This study examines cytokine expression by normal first-trimester human chorionic villi.

METHOD OF STUDY

Tissues were obtained at elective pregnancy terminations (7-9 weeks). Total RNA was isolated from chorionic villi by guanidinium isothiocynate-acid phenol extraction. A reverse transcriptase-polymerase chain reaction technique was used to examine cytokine expression. beta-Actin was used as the housekeeping gene, and mitogen-stimulated lymphocytes served as positive controls.

RESULTS

beta-Actin was uniformly expressed by all chorionic villous samples. Interferon (IFN)-alpha and -beta also were highly expressed. Moderate expression was noted for interleukin (IL)-10, IL-6, tumor necrosis factor (TNF)-alpha, and IL-1 beta. In contrast, transforming growth factor-beta 1, IFN-gamma, IL-2, and IL-1 alpha were either weakly expressed or absent in first-trimester villi.

CONCLUSIONS

Cytokines may contribute to pregnancy immunotolerance (IFN-alpha, IFN-beta, and IL-10), viral resistance (IFNs), hormone secretion (IL-1 and IL-6), and cellular remodeling (IFN-gamma and TNF-alpha) within the chorionic villous.

IFN-tau: a novel subtype I IFN1. Structural characteristics, non-ubiquitous expression, structure-function relationships, a pregnancy hormonal embryonic signal and cross-species therapeutic potentialities

IFN-tau (IFN-tau) constitutes a new class of type I IFN which is not virus-inducible, unlike IFN-alpha and IFN-beta, but is constitutively produced by the trophectoderm of the ruminant conceptus during a very short period in early pregnancy. It plays a pivotal role in the mechanisms of maternal recognition of pregnancy in ruminants and it displays high antiviral and antiproliferative activities across species with a prominent lack of cytotoxicity at high concentrations in vitro in cell culture and possibly in vivo. It exhibits high antiretroviral activity against HIV and exhibits immunosuppressive activity in a multiple sclerosis model and reduces embryo and fetal mortality by stimulation of IL-10 production. In this review all the biochemical and para-hormonal properties of this novel IFN-tau are described in detail: structural characteristics of proteins and genes, trophoblast expression, regulation of its expression, structure of its gene promoter, its absence in human species and in non-ruminant animals, the evolution of the IFN-tau genes, its structure-function relationships with its three-dimensional structure, structural localization of biological activities, its lack of cytotoxicity and its receptor. Surprisingly, for an IFN, IFN-tau is also a pregnancy-embryonic signal with paracrine antiluteolytic activity. In order to maintain luteal progesterone secretion, IFN-tau inhibits PGF-2alpha pulsatile secretion and oxytocin uterine receptivity in early pregnancy. It is believed to suppress pulsatile release of endometrial PGF-2alpha by preventing oxytocin and estrogen receptor expression. Additionally, it directly regulates prostaglandin metabolism and possibly the PGE:PGF-2alpha ratio.

Recent advances in gestational trophoblastic disease

Important advances continue to occur in both our understanding and management of gestational trophoblastic disease. Complete molar pregnancy is being diagnosed earlier in pregnancy which affects its clinical and pathological presentation. The use of chemotherapy in persistent gestational trophoblastic tumors continues to be refined and our understanding of the immunobiology of these tumors has substantially advanced.

The Structure of the Human Placenta: Implications for Initiating and Defending Against Virus Infections

The architecture of the human placenta permits an extensive and intimate association between the maternal and fetal circulations. The fetal component consists of the elaborately branched villous tree, and this is bathed directly by maternal blood circulating within the intervillous space. Whilst this arrangement may favour metabolic exchange, it poses considerable risks for the vertical transmission of pathogens. Some features of placental structure can be considered potential impediments to transmission, such as the syncytial nature of the outer villous covering, the syncytiotrophoblast, and the ability of this tissue to secrete both nitric oxide and interferons. Other features may facilitate vertical transmission, including the lack of expression of MHC Class 1 antigens by the syncytiotrophoblast, and its vesicular and immunoglobulin transport pathways. More importantly, it is known that physical defects occur in the trophoblast layers at all stages in gestation. Whilst repair processes have been identified it must be assumed that pathogens or infected maternal white cells have access to the trophoblastic basement membrane, albeit transiently. The universal nature of these defects suggests that the trophoblast cannot be of paramount importance in the prevention of transmission. Rather, the defence mechanisms must lie either at the level of the basement membrane or within the villous core. There they may be represented by the resident macrophage population or the capillary endothelial cells and their junctional complexes. Consequently, the placenta should be viewed as an active rather than a passive barrier. Copyright 1997 by John Wiley & Sons, Ltd.

Distribution of type-I interferon-receptors in human first trimester and term placental tissues and on isolated trophoblast cells

PROBLEM

Type-I interferon (IFN) is the protein recognizing pregnancy in ruminants. Although IFN is secreted in early pregnancy, its role is not still clear in other species. Like other cytokines, IFN exerts its biological functions through specific membrane receptors. We have investigated the potential action of IFN in human pregnancy by studying the distribution of the receptors in the human placenta.

METHOD

Reactivity to monoclonal antibodies (mAbs) to the type-I IFN-receptor (R) was analyzed by immunohistochemistry in human placental tissues and in cytospins of first trimester trophoblast cells.

RESULTS

Type-I IFN-R immunoreactivity was observed mostly in first trimester villous cytotrophoblasts and in the cytotrophoblast cell columns. Trophoblast in the decidua, the epithelium of the uterine glands, and most of the isolated trophoblast cells were also immunoreactive.

CONCLUSION

The expression of type-I IFN-R in the highly proliferating and migrating trophoblast suggests that this cytokine has a role in trophoblast growth and invasion.