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Y W Loke

Publications and source records attributed to Y W Loke.

At least 73 records · Page 4Linked to original sources
PubMed1994

Expression of c-kit and kit ligand at the human maternofetal interface.

Kit ligand, or stem cell factor, is a recently identified growth factor, which binds to and activates the c-kit proto-oncogene, and which has been shown to act synergistically with other haematopoietic growth factors in the bone marrow. We have previously shown that several isoforms of kit ligand, which arise due to alternative splicing, are expressed in human placenta. In order to elucidate the role of c-kit and its ligand during human placental development we have investigated the expression of c-kit and kit ligand in human first trimester and term placenta as well as in pregnant and non-pregnant endometrium, by immunocytochemistry and flow cytometric analysis. In non-pregnant endometrium no expression of kit ligand was seen. By contrast, in first trimester decidua, kit ligand was strongly expressed by the arterial media of maternal blood vessels. Kit ligand was also expressed throughout pregnancy by invasive fetal extravillous trophoblast, and by fetal fibroblasts within the placental villi. c-kit was found to be expressed on Hofbauer cells within the chorionic villi, and by decidual macrophages at all stages in pregnancy. c-kit was also detected on the small CD56dim subset of uterine large granular lymphocytes which form the major leukocyte population in human first trimester decidua. Our results suggest that kit ligand may be involved in the regulation of fetal macrophages, and in particular in signalling between invading extravillous trophoblast which expresses kit ligand, and maternal leukocytes bearing the c-kit receptor.

Amino Acid Sequence↗
PubMed1994

Reciprocal expression of epidermal growth factor receptor (EGF-R) and c-erbB2 by non-invasive and invasive human trophoblast populations.

Trophoblast invasion of the maternal uterus during human placentation is a highly complex process involving proliferation, migration and cell differentiation. Tyrosine kinase receptors are known to be involved in such functions. The epidermal growth factor-receptor (EGF-R) and c-erbB2 proto-oncogene products are two closely related tyrosine kinase receptors which are expressed in high amounts in human placenta. In this study, we have investigated the expression of EGF-R and c-erbB2 proteins by different trophoblast populations using immunohistochemistry. EGF-R was expressed by proliferative villous cytotrophoblasts, but not by non-proliferative, invasive, extravillous cytotrophoblasts. In contrast, c-erbB2 was expressed by invasive extravillous trophoblasts (EVT) but not by villous cytotrophoblasts. Expression of both receptors was seen only by the terminally differentiated placental bed giant cell and villous syncytiotrophoblast populations. This precise spatial expression suggests that EGF-R plays an important role in trophoblast proliferation whereas c-erbB2 may be important for trophoblast invasion and differentiation. The surface expression of these receptors on normal isolated first trimester trophoblasts and on choriocarcinoma cell lines was also investigated by flow cytometry, and compared with that of the c-erbB2-overexpressing mammary tumour cell line BT474. Isolated trophoblasts were shown not to overexpress c-erbB2, and no differences in either EGF-R or c-erbB2 expression were seen between normal and malignant trophoblasts.

Breast Neoplasms↗
PubMed1994

Expression of adhesion molecules by endovascular trophoblast and decidual endothelial cells: implications for vascular invasion during implantation.

During the process of implantation, maternal spiral arteries within the decidua are invaded by trophoblast cells that adhere to and migrate along the luminal surface of the vascular endothelial cells. This phenomenon resembles the events that occur during the migration of neutrophils into an acute inflammatory site, therefore it is possible that similar mechanisms are involved. Indeed, previous observations have shown that endovascular trophoblast expresses the blood group-related antigen sialyl Le(x). In this study, we show, by immunohistology, the expression of both E- and P-selectin by vascular endothelial cells only in the decidua basalis and not in decidua parietalis. In contrast, ICAM-1 is expressed by all vascular endothelium throughout the decidua. Expression of VCAM-1 is variable at the implantation site, and is not expressed by vascular endothelial cells in decidua parietalis. Interestingly, we demonstrate the strong expression of a polysialylated form of NCAM by endovascular trophoblast. Our data suggests that vascular invasion by trophoblast is regulated by the expression of appropriate adhesion molecules which permit interaction between endovascular trophoblast and decidual endothelial cells.

Cell Adhesion Molecules↗
PubMed1994

Production of granulocyte-macrophage colony-stimulating factor by human trophoblast cells and by decidual large granular lymphocytes.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a classical haematopoietic cytokine which has been implicated in placental growth and development. In this study, we investigated the production of GM-CSF in human first trimester pregnancy by the predominant uterine lymphocyte population of decidual CD56+ NK cells (large granular lymphocytes) and the factors that influence this production using enzyme-linked immunosorbent assays (ELISAs) and bioassays, supplemented by immunocytochemistry. We have also investigated and compared production of GM-CSF by human first trimester trophoblast and by JEG-3 and JAR choriocarcinoma cells. Our data show that appreciable amounts of GM-CSF are produced in first trimester maternal decidua and that a significant component of this secretion was from decidual large granular lymphocytes (LGL). Production of GM-CSF by LGL was constitutive and considerably greater than that of freshly isolated peripheral blood leukocytes. GM-CSF secretion by decidual LGL could be enhanced by co-culture on a monolayer of decidual stromal cells, and could also be increased in a dose-dependent manner by stimulation with interleukin-1 (IL-1) or IL-2. IL-4, IL-6, tumour necrosis factor alpha (TNF alpha), transforming growth factor beta (TGF beta), interferon alpha (IFN alpha) and IFN gamma individually had no effect on GM-CSF secretion, although IL-4, TGF beta and IFN alpha all inhibited the action of IL-2. IFN gamma had no effect on the IL-2-induced GM-CSF secretion, but did antagonize the action of IL-1. Normal human first trimester trophoblast was also found to produce GM-CSF, although no production whatsoever was seen by JEG-3 or JAR choriocarcinoma cells. These results suggest that GM-CSF from uterine lymphocytes, and from trophoblast itself, may influence placental growth and development in both a paracrine and an autocrine manner.

Antigens, CD↗
PubMed1993

Differential nuclear expression of enhancer A DNA-binding proteins in human first trimester trophoblast cells.

In order to investigate the possible molecular regulatory mechanisms that repress classical HLA class I and stimulate nonclassical HLA-G and E-class I gene transcription in human trophoblast cells, we searched for the nuclear expression of the enhancer A DNA-binding proteins of the KBF1/NF-KB/rel family. Using both purified extravillous cytotrophoblast and villous syncytiotrophoblast from first trimester human placenta, it appeared that members of this family were present in the cytotrophoblast and absent in the syncytiotrophoblast. First, using the double stranded enhancer A DNA nucleotidic sequence that contains the palindromic KB site, known to be the binding site of the p50 subunits of KBF1-NF-KB and c-rel factors, we demonstrated, by band-shift assay, that binding activity, inhibited by addition of anti-p50 polyclonal serum, was present in cytotrophoblast as well as control maternal decidual cells, embryonic fibroblasts, and the trophoblast-derived JAR cell line. In contrast, this DNA-protein complex was undetectable in syncytiotrophoblast nuclear extracts. The specificity of this protein-DNA complex was further demonstrated by its disappearance upon competition with an excess of cold homologous nucleotidic competitor. Other nucleoprotein complexes were also detected in all nuclear extracts, including syncytiotrophoblast, that were competed out by an excess of cold enhancer A competitor DNA but were not affected by the addition of anti-p50 or anti-NF-KB sera, suggesting the presence of additional enhancer A-binding factors different from the KBF1/NF-KB/rel family. Second, using a Western immunoblot analysis, a doublet around 85 kDa was specifically stained by the same anti-p50 serum in cytotrophoblast, maternal decidual cells, embryonic fibroblasts, and the JAR nuclear extracts whereas no signal was obtained in syncytiotrophoblast. Finally, immunofluorescence cell staining using the same anti-p50 serum showed a positive staining in both cytoplasm and nucleus of cytotrophoblast and its absence in syncytiotrophoblast. We hypothesize that this enhancer A DNA-binding factor might represent the c-rel trans-acting factor, related to p50/KBF1/NF-KB proteins, and we discuss its possible relevance to the HLA class I transcription in human tissues.

Base Sequence↗
PubMed1993

Expression of adhesion molecules by human decidual large granular lymphocytes.

This study has examined the expression of adhesion molecules by uterine-specific CD56bright CD16-CD3- large granular lymphocytes using flow cytometry and immunohistology. Data are compared with those obtained after IL-2 stimulation and with peripheral blood CD56+ cells. We have found that decidual CD56bright cells strongly express three fibronectin receptors, alpha 4 beta 1, alpha 5 beta 1, and alpha 4 beta 7. The HML-1 antigen is also expressed. The beta 2 integrins are also found on decidual CD56+ cells although, apart from CD11c, these are present at levels lower than those of corresponding cells in blood. After IL-2 stimulation there is a considerable increase in CD11a/CD18 expression on CD56bright cells. Both ICAM-1 and NCAM are found on CD56bright cells at higher levels compared to those of peripheral blood CD56+ cells. This pattern of expression of beta 1 and beta 2 integrins and members of the immunoglobulin superfamily must have important implications in the behaviour of decidual LGL. These adhesion molecules are also likely to be important in the recruitment and retention of CD56bright LGL in the decidual microenvironment particularly as the specialised decidual extracellular matrix and uterine LGL appear concomitantly at the time of implantation.

Antigens, CD↗
PubMed1993

Effect of IFN-gamma and IFN-alpha on killing of human trophoblast by decidual LAK cells.

Human decidual large granular lymphocytes are capable of killing both normal trophoblast and choriocarcinoma cells after stimulation with recombinant interleukin-2 (rIL-2) in vitro. We now show that pre-treatment of normal trophoblast and JEG-3 choriocarcinoma cells with interferon-gamma (IFN-gamma) protects these target cells from killing by decidual effectors, although pre-treatment with interferon-alpha (IFN-alpha) had no such effect. In contrast, JAR choriocarcinoma cells were readily killed before and after exposure to both IFN-gamma and IFN-alpha. This protective effect might be due to upregulation of non-classical trophoblast HLA Class I molecules, as IFN-gamma but not IFN-alpha enhances Class I surface expression in both normal trophoblast and JEG-3 choriocarcinoma cells. JAR cells, however, are constitutively and inductively negative for Class I expression.

Cell Death↗
PubMed1993

In situ hybridization and northern blot demonstration of HLA-G mRNA in human trophoblast populations by locus-specific oligonucleotide.

Trophoblast cells from normal first trimester pregnancies have been shown to express the nonclassical class I molecule, HLA-G, which is nonpolymorphic and has a heavy chain of 40 kD. In this study, in situ hybridization experiments were performed using a biotinylated HLA-G specific oligonucleotide on sections of normal placenta including the implantation site. HLA-G mRNA was identified in all extravillous trophoblast populations including the cytotrophoblast cell columns, interstitial trophoblast, endovascular trophoblast, and placental bed giant cells. In addition, villous cytotrophoblast and villous mesenchymal cells also contained HLA-G transcripts, but villous syncytiotrophoblast was always negative.

Blotting, Northern↗
PubMed1993

Expression of perforin, granzyme A and TIA-1 by human uterine CD56+ NK cells implies they are activated and capable of effector functions.

At the time the human placenta is established, the uterine mucosal lining (decidua) is infiltrated by abundant CD3- CD56bright natural killer (NK) cells. NK cells circulating in blood are known to contain perforin and granzyme A in their cytoplasmic granules. TIA-1, an RNA-binding protein capable of inducing DNA fragmentation, has also been found in the granules of cytolytic cells. In this paper, we demonstrate the presence of perforin, granzyme A and TIA-1 in the granules of uterine NK cells. Sixteen sections of non-pregnant endometrium throughout the menstrual cycle and six sections of early decidua, together with cytospins of four preparations of isolated decidual leukocytes were stained by both immunohistology and immuno-electron microscopy to localize perforin, granzyme A and TIA-1 to the cytoplasmic granules of CD56+ cells. The presence in vivo of these cytolytic molecules in a normal physiological situation implies that these uterine NK cells may have effector functions in the control of normal placentation.

Antigens, CD↗
PubMed1993

Expression of integrins by human trophoblast and differential adhesion to laminin or fibronectin.

The process of placental implantation involves a series of transformations of trophoblast from a single polarized epithelial layer resting on a basement membrane (villous trophoblast), to cellular aggregates (trophoblast columns) which ultimately disperse to invade uterine decidua as individual cells (interstitial trophoblast). Such tissue re-modelling is associated with changes in the constituents of the extracellular matrix and in the expression of matrix receptors by the cells, the most relevant being the family of integrins which bind to laminin and fibronectin. In this study we show, by immunohistology and flow cytometry, a gradual loss of laminin receptors with the concomitant acquisition of fibronectin receptors as trophoblast is transformed from the villous phenotype, through the cell columns, into the extravillous population. The pattern of staining for the alpha 5, alpha 6, beta 1 and beta 4 subunits indicates that the integrins expressed by trophoblast are predominantly the alpha 5 beta 1 and the alpha 6 beta 4 heterodimers. We have also shown that isolated trophoblast cells assume a flattened, sessile phenotype when cultured on laminin but exhibit a more spreading, motile morphology when plated on fibronectin. In addition, numerous multinucleated giant cells are observed on a fibronectin substrate. Our data suggest that the relative expression of laminin and fibronectin receptors may determine the morphology and behaviour of trophoblast during the process of implantation.

Cell Adhesion↗
PubMed1993

Expression of the colony stimulating factor-1 receptor (c-fms product) by cells at the human uteroplacental interface.

BACKGROUND: The hematopoietic growth factor colony-stimulating factor-1 (CSF-1) and its receptor (encoded by the proto-oncogene c-fms) are implicated in the regulation of human placental development. EXPERIMENTAL DESIGN: In this study, we have performed a detailed immunohistochemical localization of the CSF-1 receptor (CSF-1R) on cells of the uteroplacental interface in human first trimester pregnancy, supplemented by Northern blot, in situ hybridization, and flow cytometric analysis. CSF-1R expression by JEG-3 and JAR choriocarcinoma cells was also investigated. RESULTS: c-fms mRNA was detected in primary cultures of first trimester trophoblast and was localized to the extravillous cytotrophoblast columns streaming off the anchoring villi. CSF-1R was expressed by fetal Hofbauer cells in the mesenchyme of the chorionic villi, and this expression increased considerably from first trimester to term. No expression was seen on first trimester and term villous cytotrophoblast. CSF-1R expression on villous syncytiotrophoblast was absent at 6 weeks, strongest at 8-10 weeks, and faded by 12 weeks. First trimester extravillous cytotrophoblast columns were strongly and consistently positive for CSF-1R expression, as was the superficial shell of extravillous trophoblast over the maternal decidua. However, with deeper invasion and terminal differentiation into placental bed giant cells, this expression became weak or absent. Endovascular trophoblast was also only weakly positive for CSF-1R. At the implantation site itself, large numbers of decidual macrophages and CD3-, CD56bright large granular lymphocytes were seen. The macrophages expressed CSF-1R strongly, but large granular lymphocytes, decidual stromal cells, glandular epithelium, and endothelial cells were found to be negative for CSF-1R expression. No CSF-1R expression was detected in JAR choriocarcinoma cells, but CSF-1R was present in first trimester cultured trophoblast and JEG-3 choriocarcinoma cells, although this was shown to be intracellular. CONCLUSIONS: These results suggest that CSF-1 may regulate invasion and differentiation of human placental trophoblast, depending upon the spatial and temporal distribution of its receptor. CSF-1 may also influence placental development and function by acting via decidual and fetal macrophages, which are the other cell populations expressing the receptor.

Blotting, Northern↗
PubMed1992

The response of human decidual leukocytes to IL-2.

The phenotype of human decidual leukocytes, composed predominantly of CD3-CD16(-)-CD56bright cells, was examined after culture with IL-2 by immunofluorescence and flow cytometry. After IL-2 stimulation the phenotype became like that found on classical NK cells, with an increased proportion of cells expressing CD16. The IL-2R alpha was absent before and after IL-2 stimulation. However, the intermediate affinity receptor, IL-2R beta, was expressed by CD56bright decidual cells, but this receptor was downregulated after IL-2 stimulation. IL-2-induced proliferation of CD56+ decidual cells could be blocked using TU27, a monoclonal antibody to the IL-2R beta. These findings indicate activation of decidual leukocytes by IL-2 occurs through the IL-2R beta alone.

Antigens, CD↗
PubMed1992

Evidence for the expression of granulocyte-macrophage colony-stimulating factor receptors by human first trimester extravillous trophoblast and its response to this cytokine.

The present study has demonstrated that human extravillous trophoblast cells isolated from first trimester placentae can bind granulocyte-macrophage colony-stimulating factor (GM-CSF). We have used a technique which incorporates a phycoerythrin (PE)-conjugated GM-CSF in association with a monoclonal antibody against trophoblast (BC-1) in single and double flow cytometric analysis. Trophoblast cells are also observed to show increased DNA synthesis in response to GM-CSF as assayed by [3H]thymidine incorporation and proliferative activity as demonstrated by double immunocytochemical staining of cells with a trophoblast cytokeratin marker (PKK1) and for the nuclear proliferation antigen (Ki-67). These findings provide evidence that human extravillous trophoblast expresses receptors for GM-CSF and responds to this cytokine.

Antibodies, Monoclonal↗
PubMed1991

Human extravillous trophoblast MHC class I expression is resistant to regulation by interferon-alpha.

We have shown that MHC Class I antigen expression by first trimester human extravillous trophoblast cells is resistant to upregulation by IFN-alpha while embryonic fibroblasts of the same gestational age are responsive. This is in contrast to our previous finding that IFN-gamma increases both Class I mRNA and surface expression in these trophoblast cells. It would appear that human trophoblast has differential susceptibility to the effects of the two classes of IFN.

Female↗
PubMed1991

On the nature and function of human uterine granular lymphocytes.

The 'foetal allograft' concept of the maternal-foetal relationship is currently being questioned. This is partly due to the increasing awareness of uterine large granular lymphocytes, a subset of natural killer cells found in the human endometrium at the time of placentation. Analogous cells are present in several species. The possible role of these cells in the regulation of the trophoblast-maternal interface is discussed here by Ashley King and Yung Wai Loke.

Animals↗
PubMed1991

Isolation of endothelial cells from human first trimester decidua using immunomagnetic beads.

A technique was developed for the isolation of purified endothelial cells from first trimester decidual tissue, using QB End/40-coated magnetic polystyrene beads (Dynabeads). QB End/40 is an endothelial-specific monoclonal antibody which reacts with the coagulation cascade co-factor, thrombomodulin. Small endothelial cell aggregates were released from first trimester decidua by the sequential use of collagenase and trypsin. This dissociation method yielded 15-20% endothelial cells which were further purified to greater than 90% homogeneity by rosetting with QB End/40-Dynabeads. Cultures of purified decidual endothelial cells provide a useful tool for investigating cell-cell interaction in the first trimester placental bed.

Cell Separation↗