Immunohistochemical localization of hCG alpha, hCG beta CTP, hPL and SP1 on villous and extravillous trophoblasts in normal human pregnancy

Trophoblasts are divided into villous trophoblasts and extravillous trophoblasts, depending on whether they constitute a villous structure, and cell columns intervene between them. We conducted an immunohistochemical localization of human chorionic gonadotropin (hCG) alpha, hCG beta C-terminal peptide (CTP), human placental lactogen (hPL) and pregnancy-specific beta 1-glycoprotein (SP1) on the trophoblasts of normal human pregnancy, using forty-one hysterectomized pregnant uteri (6-22 weeks). In villous trophoblasts, the capacity to synthesize hCG alpha, hCG beta CTP, hPL and SP1 seemed to develop according to the morphological change from mononuclear cells to multinuclear cells. In contrast, the synthetic capacity of these proteins seemed not to correspond with the morphological change in extravillous trophoblasts: The location of hCG alpha, hCG beta CTP and SP1 was restricted to the mononuclear trophoblasts in the superficial decidua, while hPL was present extensively in extravillous trophoblasts, including multinuclear trophoblasts in the deciduomuscular junction. Therefore, it may be reasonably said that extravillous trophoblasts have many biological features distinct from villous trophoblasts and differentiate in an independent manner. Mononuclear trophoblasts in the cell column were negative for these proteins, which, together with morphological observations, strongly suggest the germinative nature of these cells.     

HLA expression by trophoblast of invasive moles

HLA expression by the trophoblast in invasive hydatidiform mole was analysed by immunoperoxidase staining. In the invading villi of an invasive mole, villous trophoblast, both syncytiotrophoblast and cytotrophoblast, failed to show a positive reaction for HLA-A, -B and -C and HLA-DR. By contrast, extravillous trophoblast showed an intense reaction for HLA-A, -B and -C. The distribution of HLA antigens in the invading villi was the same as in the non-invading villi, and the antigens were also indistinguishable from those noted in non-invasive hydatidiform moles. The histopathology of invasive mole may suggest that it is a malignant neoplasm. This immunohistochemical study, however, lends support to the current view that invasive mole is a variant of a benign hydatidiform mole rather than a form of malignant trophoblastic disease.     

Morphological and immunohistochemical study on specimens of trophoblastic diseases in which the presence of a villous formation could not be established

The histopathological discrimination between malignant trophoblastic diseases and benign trophoblastic diseases depends on the presence or absence of a villous structure. However, molar extravillous trophoblasts and cells in some placental site trophoblastic tumors (PSTT) of a benign nature, lack a villous structure. We therefore observed the morphology of trophoblastic cells which do not constitute a villous structure, including choriocarcinoma cells, and analyzed the location of placental proteins in these cells immunohistochemically. The results were as follows: 1. Molar extravillous trophoblasts were composed of large mononuclear cells and multinuclear cells. Most of them were positive for hPL and negative for hCG and SP1. 2. Choriocarcinoma consisted of cytotrophoblast-like cells, syncytiotrophoblast-like cells, large mononuclear cells and multinuclear cells resembling large mononuclear cells. HCG was noted in syncytiotrophoblast-like cells and large mononuclear cells, while hPL and SP1 were found only in syncytiotrophoblast-like cells. 3. PSTT was made up of large mononuclear cells and multinuclear cells which contained abundant hPL and very little hCG and SP1 or none at all. Molar extravillous trophoblasts were clearly distinguishable from choriocarcinoma cells in terms of their morphology and the location of placental proteins. In contrast, it seemed difficult to distinguish cells of PSTT from molar extravillous trophoblasts on a cell level.     

Linkage of human chorionic gonadotrophin and placental lactogen biosynthesis to trophoblast differentiation and tumorigenesis

Normal trophoblast of the human placenta elaborates at least two major protein hormones, chorionic gonadotrophin (hCG) and placental lactogen (hPL). Molar and choriocarcinoma tissues characteristically synthesize large amounts of hCG and hPL. To examine the role of trophoblast differentiation in the expression of the hCG and hPL genes, we studied the cytological distribution of their mRNAs in tissue sections of human hydatidiform mole and choriocarcinoma by in situ hybridization. Histologically, these tissues are in different stages of cellular differentiation. In normal placenta, hCG alpha/beta mRNA can be localized to some cytotrophoblasts and primarily to the syncytium, whereas hPL mRNA appears only in the syncytial layer. In hydatidiform mole, which still retains placental villous morphology, the hPL gene and hCG alpha and beta genes are expressed but are poorly localized because of the admixture of cyto- and syncytiotrophoblasts. By contrast, choriocarcinoma, which is devoid of placental villous pattern but in which the cyto- and syncytiotrophoblast-like components are distinguishable, expresses hCG alpha and beta in the syncytial-like areas but little, if any, hPL. These results suggest that a certain level of trophoblast differentiation, such as villous formation, is associated with hPL expression, while the hCG alpha gene and the hCG beta gene can be expressed in more disorganized tissues which contain cytotrophoblastic elements.     

Stimulation of hCG and inhibition of hPL in isolated human trophoblast cells in vitro by glycodelin A

The immunosuppressive protein glycodelin A (formerly named PP14) is produced by human decidua and secreted in the maternal circulation. Glycodelin A concentrations in serum have been used as indicators of endometrial function. The purpose of this study was to investigate the effect of glycodelin A on human chorionic gonadotropin (hCG) and human placental lactogen (hPL) release by freshly isolated cytotrophoblasts (in vitro). Cytotrophoblasts have been prepared from human term placenta by the three-step trypsin-DNase dispersion method of villous tissue followed by a percoll gradient centrifugation step. When placed in culture, the isolated mononuclear trophoblasts differentiated into syncytial counterparts within 12-72 h after plating. Trophoblasts were incubated with varying concentrations (60-300 microg/ml) of glycodelin A. Glycodelin A was isolated and purified by chromatographic methods from amnion fluid. Supernatants of the trophoblast cell cultures were assayed for hCG and hPL by immunological methods. The release of hCG is increased in glycodelin A-treated trophoblast cell cultures compared to untreated trophoblast cells. Glycodelin A inhibits the production of hPL in vitro. Differences in Glycodelin A stimulated cells and untreated controls are statistical significant. hCG and hPL are markers for the differentiation process of trophoblast cells to syncytial trophoblasts. The results imply that glycodelin A secreted by decidualised endometrium modulates endocrine function, as well as the differentiation of trophoblasts in culture.     

Villous culture of first trimester human placenta--model to study extravillous trophoblast (EVT) differentiation.

During implantation and subsequent placentation the human extravillous trophoblast (EVT) cells invade the endometrium and maternal vasculature within the uterus. The origin of the EVT and signals triggering its differentiation, migration and invasion are poorly understood. First and second trimester human chorionic villi explants were used as a source of EVT and a variety of substrates which resemble extracellular matrix (ECM) in vivo have been tested to induce EVT differentiation and migration. The obtained results demonstrate that villous explants from both 5-7 and 8-10 weeks of gestation give rise to EVT cells in vitro if maintained on the surface of Matrigel or decidual extract supplemented collagen gel. Fetal calf serum (FCS) supplemented media was essential for EVT differentiation and villous trophoblast viability. Immunostaining of both EVT cells and cells from the cytotrophoblastic column with monoclonal antibody Ki67 (cell proliferation marker) indicate that EVT cells differentiate in vitro by proliferation from the tip of anchoring villi. These mononucleated, round-shaped, migrating cells are HLA-A,B,C class I antigen (W6/32) antibody and low molecular weight cytokeratin positive, and do not immunostain with PAI-1 (plasminogen activator inhibitor) and HPL antibodies. Differentiation of EVT was restricted to first trimester villous tissue; explants from second trimester placentae did not give rise to EVT. Tissue viability as monitored by glucose utilization, lactate, progesterone and hCG production rates correlated with EVT differentiation. The production rates for hCG demonstrated significant variation among individual placentae and was maintained constant for 10 days consistently only in explants cultured on decidual extract supplemented collagen matrix. The described villous tissue culture system may be, therefore, a unique in vitro model to study proliferation and differentiation of EVT from cytotrophoblastic columns, the regulation of EVT proliferation and differentiation, the role of ECM in the induction of the migration and the interaction of extravillous and villous trophoblast at the level of the cytotrophoblastic column.     

Integrin alpha5 is involved in fibronectin-induced human extravillous trophoblast invasion

To identify the molecules involved in human extravillous trophoblast (EVT) invasion, we raised murine mAbs that react with EVTs and obtained one mAb (CHL3) that inhibited invasion of a human choriocarcinoma-derived cell line, BeWo cells. The N-terminal 22 aminoacid sequence of the CHL3 antigen (150kDa) purified from placental tissue completely matched that of integrin alpha5, which is known to interact with fibronectin. Double immunohistochemical staining and flow cytometry confirmed the reactivity of CHL3 with integrin alpha5 and its expression on the surface of BeWo cells and human EVTs isolated from villous explant cultures. CHL3 mAb inhibited the attachment of human EVTs and BeWo cells to fibronectin-coated dishes, but not to Matrigel dishes. In the Matrigel invasion assay supplemented with or without fibronectin, the invasion of isolated EVTs and BeWo cells was attenuated by treatment with CHL3 without affecting cell proliferation. During invasion assays, the production of matrix metalloproteases 2 and 9 was not changed by CHL3. These findings suggest that interaction with fibronectin through integrin alpha5 plays an important role in human extravillous trophoblast invasion.     

A study on the role of DNA methylation within hCG and hPL genes in trophoblastic disease

It has been shown that the extent of methylation of cytocine in DNA is inversely correlated with gene expression in many cases. The DNAs extracted from placental tissue, hydatidiform mole and choriocarcinoma tissue were examined to see whether the extent of cytocine methylation is correlated to the gene expression of placental peptide hormones and the transformation of trophoblast. First of all we measured the amount of methylated cytocine per total DNA with HPLC. We then examined cytocine methylation in hCG alpha,beta and hPL genes using methylation sensitive (Hha I, Hpa II) and non sensitive (Msp I) restriction enzymes and molecular hybridization. During pregnancy the total amount of methylated cytocine measured with HPLC increases gradually from 0.72 mol.% at first trimester to 0.92 mol.% at term. The DNA of WBC showed a higher level of methylated cytocine than placental DNA. The extent of DNA methylation in the peptide hormone genes increases during placental development. Hypomethylation in the hCG alpha gene was also seen in molar tissue which expresses a high amount of hCG. Therefore it is inversely correlated that gene expression of hCG alpha,beta and the extent of DNA cytocine methylation. Furthermore some restriction polymorphisms were observed with Msp I in hCG alpha and hPL genes which might be related to malignant transformation of the trophoblast.     

Circulating levels of pregnancy proteins in early and late pregnancy in relation to placental tissue concentration.

The concentrations of human chorionic gonadotrophin (hCG), human placental lactogen (hPL), pregnancy specific beta 1 glycoprotein (SP1), ferritin (PP2) and placental protein 5 (PP5) were examined in maternal serum and placental tissue in early and late pregnancy. The circulating concentration of hPL, SP1, and PP5 were higher during late pregnancy than early pregnancy, that of hCG lower, and ferritin (PP2) levels showed no difference. Placental tissue levels of hPL and SP1 were higher in late pregnancy, hCG levels lower, and ferritin (PP2) and PP5 showed no change. The ratio of the concentration in maternal serum to that in placental tissue increased during pregnancy for all proteins with the exception of ferritin. It is proposed that the mechanism of secretion of trophoblast specific proteins varies widely and that this should be taken into account in the clinical interpretation of circulating levels in the mother.     

Human choriogonadotropin (hCG) and placental lactogen (hPL) inhibit interleukin-2 (IL-2) and increase interleukin-1 beta (IL-1 beta), -6 (IL-6) and tumor necrosis factor (TNF-alpha) expression in monocyte cell cultures.

The effect of the human trophoblast hormones chorionic gonadotropin (hCG) and placental lactogen (hPL) on the expression of cytokines in peripheral blood mononuclear cell cultures was followed under a variety of culture conditions, (a) phytohemagglutinin stimulated cells (PHA-MSC), (b) allogenic mixed cells (AMC) and (c) spontaneously proliferating cells (SPC). A dose dependent enhanced release of IL-6, IL-1 beta and TNF-alpha by hCG and hPL was observed under all culture conditions. However, an inhibitory effect on the IL-2 release was seen in PHA-MSC by hPL and in AMC by hPL and hCG. The role of the suppression of IL-2 production/release on cytotoxicity towards trophoblast is discussed. These results suggest a sensitive, dose dependent hormonal control of the modulation of the immune response during pregnancy and strengthen the concept of a distinct regulation of monocytes and lymphocyte subpopulation by trophoblast hormones.     

Apoptosis and its role in the trophoblast

During early placentation the trophoblast of the human placenta differentiates to the villous and extravillous types of trophoblast. Villous trophoblast provides the epithelial cover of the placental villous trees in direct contact to maternal blood. Extravillous trophoblast invades maternal uterine tissues thus directly contacting maternal stromal and immune cells. A subset of extravillous trophoblast, endovascular trophoblast initially occludes the lumen of spiral arteries and comes into direct contact with maternal blood. In recent years apoptosis has been described in both types of trophoblast and the importance of this cascade for the normal function of the trophoblast has become obvious. One feature of serious conditions such as preeclampsia or intrauterine growth restriction is changes in apoptosis regulation in villous and/or extravillous trophoblast resulting in altered trophoblast invasion and/or shedding into the maternal circulation. This review summarizes recent findings on trophoblast apoptosis in normal and pathologic pregnancies.     

Oxygen tension directs the differentiation pathway of human cytotrophoblast cells

During placental development, human cytotrophoblast cells can differentiate to either villous syncytiotrophoblast cells or invasive extravillous trophoblast cells. We hypothesize that oxygen tension plays a critical role in determining the pathway of cytotrophoblast differentiation. A highly purified preparation of cytotrophoblast cells from human third trimester placenta was cultured for 5 days in either 20% or 1% oxygen tension. The cells incubated at 20% oxygen formed a syncytium as determined by immunohistochemistry using an anti-desmosomal protein antibody that identifies cell membranes. In addition, the mRNA was markedly induced for syncytin, a glycoprotein shown to be essential for syncytiotrophoblast formation, and for human placental lactogen (hPL), which is a specific marker for syncytiotrophoblast cells. In contrast, the cell incubated at 1% oxygen tension did not fuse by morphologic analysis and did not express syncytin or hPL mRNA. However, these cells expressed abundant amounts of HLA-G, a specific marker for extravillous trophoblast cells, which was not seen in cells incubated at 20% oxygen tension. These results suggest that low oxygen tension directs differentiation along the extravillous trophoblast cell pathway while greater oxygen tension directs differentiation along the villous trophoblast cell pathway.     

The concentrations of SP1 beta and SP1 alpha in retroplacental and peripheral blood at term

The concentrations of the two components of Schwangerschaftsprotein 1 (SP1 beta and SP1 alpha), human chorionic gonadotrophin (hCG) and human placental lactogen (hPL), were measured in peripheral venous blood and in retroplacental blood at term delivery in 22 women. Like hCG and hPL, the values of SP1 alpha were higher in the retroplacental than in the peripheral blood, as might be expected with placental secretory products. On the other hand, the concentration of SP1 beta showed a reverse gradient, being higher in the peripheral than in retroplacental blood.     

Placenta accreta: an immunohistological study of trophoblast populations

Trophoblast populations in four cases of placenta accreta were characterized using antibodies directed against cell membrane antigens, placental hormonal products and low-molecular-weight cytokeratins in standard immunoperoxidase techniques. The results obtained with antibody to syncytiotrophoblast membrane (rabbit anti-StMPM), antibody to an epithelial membrane antigen (HMFGI) and a cytokeratin marker (CAM 5.2) appeared identical to those reported for normal term placental tissues. Similarly the localization of human placental lactogen (hPL), human chorionic gonadotrophin (hCG) and pregnancy-specific beta 1-glycoprotein (SP1) within trophoblast populations in placenta accreta was identical to their reported distribution in term placenta. However, increased reactivity at the villous-maternal junction was demonstrated with NDOGI, an antibody raised against term syncytiotrophoblast membrane and directed against hyaluronic acid. NDOGI reactivity at this site is normally maximal during early placental development and is virtually absent in the third trimester. The results suggest that placenta accreta does not arise through excessive trophoblast invasiveness or proliferation and the absence of decidua is of more importance in the pathogenesis. Trophoblast may regulate its development at an unfavourable intramyometrial implantation site by the production of hyaluronic acid.     

The relation between the concentration of placental specific proteins in retroplacental and peripheral blood.

Concentrations of four placental proteins: human placental lactogen (hPL), placental protein 5 (PP5), pregnancy specific beta 1 glycoprotein (SP1) and human chorionic gonadotrophin (hCG), and a normal serum component, alpha 2 macroglobulin, were measured in the peripheral circulation and in blood obtained from the retroplacental space in 20 women at term delivery. Levels of hPL and PP5 were higher in the retroplacental blood than in the peripheral circulation in all patients. By contrast, levels of SP1 and hCG were consistently lower in retroplacental blood than in the peripheral circulation. Similarly, levels of alpha 2 macroglobulin were lower in the retroplacental blood. It is suggested that this 'reverse' gradient is a technical arterfact. These findings are discussed in relation to synthesis of placental proteins in a site distal to the retroplacental space, and the introduction of a technical artefact in the collection of samples.     

Antiphospholipid antibodies prevent extravillous trophoblast differentiation

OBJECTIVE: We investigated the hypothesis that antiphospholipid antibodies (aPL) have a detrimental effect on human extravillous trophoblast (EVT) differentiation into giant multinucleated cells "in vitro." DESIGN: The EVT were isolated from the placental chorion using enzymatic digestion and Percoll gradient centrifugation. After 24, 36, and 48 hours in culture, giant multinuclear cells (GMC) were identified by immunohistochemistry using antibodies to cytokeratin 7 and counted. SETTING: An academic research laboratory. PATIENT(S): Placentas were donated by women having an elective cesarean section for a normal pregnancy at term. MAIN OUTCOME MEASURE(S): This model was then used to investigate the effect of two different monoclonal aPL to beta2-glycoprotein 1 (IIC5 and ID2), and control mouse IgG antibody on EVT differentiation. RESULT(S): Freshly isolated EVT were nonproliferative but moved together losing their intervening cell walls and differentiated into GMC. Maximal numbers of GMC were detected after 48 hours of culture. The aPL, IIC5, and ID2 significantly inhibited GMC formation, whereas the mouse IgG control had no effect. CONCLUSION(S): Antiphospholipid antibodies can inhibit EVT differentiation and GMC formation "in vitro" suggesting that a failure of trophoblast differentiation and subsequent uteroplacental development may be an underlying pathology in antiphospholipid syndrome-associated pregnancy loss.     

The art of identification of extravillous trophoblast

Immunohistochemical staining with specific markers for the respective cell type facilitates tracking and identification of cells such as extravillous trophoblast in the uterine wall. Cytokeratin has been recommended as a marker for all kinds of trophoblasts and is commonly used as a marker to identify interstitial as well as endovascular trophoblast. With immunohistochemical double staining of specimens of first trimester placental bed we show that staining with anti-cytokeratin alone is not sufficient to track all routes of trophoblast invasion. Endovascular trophoblasts can be easily mixed up with endoglandular trophoblasts. Thus, additional application of specific markers for extravillous trophoblast such as anti-HLA-G is strongly recommended, ideally in combination with other markers in immunohistochemical or immunofluorescence double staining.     

Immunocytochemical localization of placental lactogen and chorionic gonadotropin in the normal placenta and trophoblastic tumors, with emphasis on intermediate trophoblast and the placental site trophoblastic tumor

This report presents preliminary observations on the immunocytochemical localization of human chorionic gonadotropin (hCG) and human placental lactogen (hPL) in placental site trophoblastic tumors, hydatidiform moles, and choriocarcinomas and compares the findings with those of a similar immunocytochemical analysis of the placenta at various stages of development. In addition to cytotrophoblast (CT) and syncytiotrophoblast (ST), a third form of trophoblast designated "intermediate trophoblast" (IT) is present during normal pregnancy and in trophoblastic disease. Intermediate trophoblastic cells are mononucleate, larger than CT, and contain more abundant eosinophilic cytoplasm, resulting in a partial resemblance to ST. Intermediate trophoblast has distinctive immunocytochemical features that distinguish it from CT and ST. The localization of hPL and hCG in both IT and ST varies with the age of the placenta, with the type of trophoblastic neoplasm, and from one specimen to another within each category of tumor. Syncytiotrophoblast may contain both hormones in large amounts, whereas IT contains hPL predominantly and hCG focally. Cytotrophoblast is devoid of hCG and hPL except in choriocarcinoma, which may show focal weak staining for hCG. Immunocytochemical identification of hCG and hPL has proved helpful in clarifying the histogenesis of trophoblastic neoplasms and may also be of value in establishing their diagnosis and in determining their prognosis.