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Y W Loke

Publications and source records attributed to Y W Loke.

At least 37 records · Page 2Linked to original sources
PubMed1999

The influence of the maternal uterine immune response on placentation in human subjects.

The immunological relationship between the mammalian fetus and its mother during pregnancy has been considered similar to that between a transplanted allograft and its recipient ever since Medawar (1953) first proposed the concept of the 'fetus as an allograft' in the early 1950s. Based on this analogy, it has been assumed that implantation of the fetal placenta in the uterus would be controlled similarly by a maternal immune response mediated by T-cells recognizing paternally-derived alloantigens expressed by the placenta. Surprisingly, recent evidence suggests that implantation might involve predominantly a novel allogeneic recognition system based on natural killer cells rather than T-cells (Loke & King, 1995). The cellular and molecular basis of this local immune interaction between the fetal placenta and maternal uterus is now the focus of intense research interest. Since aberrant implantation can cause a variety of clinical problems, including miscarriage, intrauterine growth retardation and pre-eclampsia, an understanding of the immunological mechanism by which this process is controlled could lead to the development of regimens to improve fetal growth and development.

Embryonic and Fetal Development↗
PubMed1999

Co-stimulation of human decidual natural killer cells by interleukin-2 and stromal cells.

At the late secretory phase of the menstrual cycle and in early pregnancy, the uterine mucosa is infiltrated by large numbers of natural killer (NK) cells with a distinctive phenotype (CD56bright CD16- CD3-) and large granular lymphocyte (LGL) morphology. Circulating CD56bright NK cells generally proliferate in the presence of interleukin-2 (IL-2), but it is clear that cofactors besides IL-2 are required for optimal response. In the bone marrow, this co-stimulating signal is provided by stromal cells. In the present study we observe that uterine CD56+ cells from early pregnancy decidua similarly proliferate vigorously when cultured with decidual stromal cells and a suboptimal dose of IL-2. This response is dependent on cell-cell contact, as no proliferation of decidual NK cells was observed when they were separated from stromal cells by a permeable cyclopore membrane. In addition, we have studied the expression of Bcl-2 by decidual CD56+ cells. Our results show that the microenvironment of the uterus is likely to have a significant influence on the proliferation and survival of uterine CD56+ cells.

CD3 Complex↗
PubMed1999

The role of trophoblast in the physiological change in decidual spiral arteries.

The remodelling of the maternal uterine spiral arteries during pregnancy, known as physiological change, is critical for the normal growth and development of the fetus. Controversy has surrounded the part played by fetal trophoblast in the transformation of these spiral arteries. To address this debate, a histological and immunochemical comparison of blood vessels from the implantation sites of human pregnancies of early gestation with uterine tissue where trophoblast was absent was performed. Results showed that true physiological change, with the features of medial necrosis and deposition of fibrinoid material, only occurred in the presence of trophoblast. In addition, it was found that subpopulations of trophoblast contribute differently in the process. Interstitial trophoblast-mediated destruction of the arterial media precedes replacement of the endothelial cells by endovascular trophoblast.

Arteries↗
PubMed1999

HLA-G in the human thymus: a subpopulation of medullary epithelial but not CD83(+) dendritic cells expresses HLA-G as a membrane-bound and soluble protein.

The human MHC class Ib gene HLA-G is transcribed and translated in different placental cell subpopulations during pregnancy. In addition to this restricted tissue distribution, HLA-G proteins were also recently detected in the thymus of HLA-G transgenic mice, as well as in some human thymic epithelial cells (TEC). There was a need to further define the phenotype of the HLA-G-expressing cells in the human thymus as well as the type of translated forms that they produce. Using several HLA-G-specific mAb and immunohistochemistry performed on cryosections of human thymi at different ages, we found that the HLA-G-expressing cells are present on medullary cells exhibiting the epithelial morphological type 6. Co-localization experiments performed by double or triple immunofluorescence staining demonstrate that these HLA-G-expressing cells express various cytokeratins, epithelial cell markers but not the CD83 dendritic cell marker. We further show by ELISA measurements that a subset of primary cultured human TEC also expresses soluble HLA-G. Therefore, HLA-G protein tissue distribution is not restricted solely to placental cells. A subpopulation of medullary TEC also expresses HLA-G both at their cell surface and in secreted form, raising the question of the functional significance of such MHC class Ib molecules. Whether thymic soluble and/or membrane-bound HLA-G contribute to inhibit NK cells or to a negative selection of autoreactive T cells which could be harmful in case of pregnancy and/or to a positive selection of viral peptides/HLA-G-restricted CD8(+) T cells remains to be demonstrated.

Adolescent↗
PubMed1999

Localization of leukemia inhibitory factor and its receptor in human placenta throughout pregnancy.

Mice in which the gene that encodes the receptor (R) for leukemia inhibitory factor (LIF) has been deleted show abnormal growth and development of the placenta. This indicates that LIF plays an important role in placental development. The expression of LIF-R and LIF was examined in human trophoblast and decidua using in situ hybridization and immunocytochemistry. LIF-R mRNA and immunoreactivity was localized in villous and extravillous trophoblast throughout pregnancy, and in endothelial cells of the fetal villi. Strong expression of mRNA encoding LIF was detected in decidual leukocytes, which are abundant at the implantation site. Extravillous trophoblast, which invades the maternal decidua, therefore expresses LIF-R as it moves past decidual leukocytes, which express LIF mRNA. The effect of LIF on cultured human trophoblast was examined in vitro. Recombinant human LIF had no effect on [3H]thymidine incorporation by purified extravillous trophoblast, nor on expression of integrins alpha1, alpha5, or beta1 by isolated trophoblast. These results identify fetal endothelial cells and all cells of the trophoblast lineage as targets for the action of LIF in human placenta. Although its effects on trophoblast are not yet clear, LIF appears to mediate interactions between maternal decidual leukocytes and invading trophoblast. LIF may also play a critical role in controlling angiogenesis in the placental villi, since human fetal endothelial cells express LIF-R, and mice lacking a functional LIF receptor gene show altered vascular development in the placenta.

Cell Division↗
PubMed1998

Expression of CD3 epsilon, CD3 zeta, and RAG-1/RAG-2 in decidual CD56+ NK cells.

In early pregnancy the uterine mucosa, the decidua, is infiltrated by numerous CD56bright, CD16- natural killer (NK) cells. In this paper we have shown that unlike adult peripheral blood NK cells these uterine NK cells express cytoplasmic CD3 and CD3 zeta, but CD3 gamma and CD3 delta were not found in the majority of cells. In contrast to previous reports, there was no evidence of RAG-1 nor RAG-2 expression in decidual NK cells. These findings have implications for the ontogeny and development of decidual NK cells.

CD3 Complex↗
PubMed1998

Apoptosis in the early human placental bed and its discrimination from necrosis using the in-situ DNA ligation technique.

Extensive areas of necrosis are present in the early human placental bed. Our aim was to determine whether apoptosis is also a feature. A method was therefore required to differentiate unequivocally necrosis and apoptosis. Initially, terminal deoxynucleotide transferase-mediated dUTP nick-end labelling was used to visualize apoptotic cells. However, non-specific labelling, probably due to free DNA released by necrotic cells, was excessive; thus, in-situ DNA ligation was employed. In this technique, two DNA fragments with single-base 3' overhangs and blunt-ends were labelled with a fluorochrome and then ligated to the DNA breaks on the sections. Immunolabelling for cytokeratin or leukocyte common antigen was performed to determine the phenotype of apoptotic cells identified by the in-situ DNA ligation technique. A proportion of the dying cells was confirmed to be trophoblasts. No co-localization with leukocyte common antigen was found in this region, suggesting that maternal macrophages and natural killer cells (CD56+) were not dying by apoptosis in significant numbers. In conclusion, in-situ DNA ligation in association with immunocytochemistry can readily distinguish apoptosis from necrosis in the placental bed. The results suggest that a proportion of invading trophoblast cells are eliminated by apoptosis in early pregnancy.

Apoptosis↗
PubMed1997

Human histocompatibility leukocyte antigen (HLA)-G molecules inhibit NKAT3 expressing natural killer cells.

The crucial immunological function of the classical human major histocompatibility complex (MHC) class I molecules, human histocompatibility leukocyte antigen (HLA)-A, -B, and -C, is the presentation of peptides to T cells. A secondary function is the inhibition of natural killer (NK) cells, mediated by binding of class I molecules to NK receptors. In contrast, the function of the nonclassical human MHC class I molecules, HLA-E, -F, and -G, is still a mystery. The specific expression of HLA-G in placental trophoblast suggests an important role for this molecule in the immunological interaction between mother and child. The fetus, semiallograft by its genotype, escapes maternal allorecognition by downregulation of HLA-A and HLA-B molecules at this interface. It has been suggested that the maternal NK recognition of this downregulation is balanced by the expression of HLA-G, thus preventing damage to the placenta. Here, we describe the partial inhibition of NK lysis of the MHC class I negative cell line LCL721.221 upon HLA-G transfection. We present three NK lines that are inhibited via the interaction of their NKAT3 receptor with HLA-G and with HLA-Bw4 molecules. Inhibition can be blocked by the anti-NKAT3 antibody 5.133. In conclusion, NK inhibition by HLA-G via NKAT3 may contribute to the survival of the fetal semiallograft in the mother during pregnancy.

Cells, Cultured↗
PubMed1997

Expression of killer cell inhibitory receptors on human uterine natural killer cells.

The establishment of the human placenta in early pregnancy is characterized by the presence of large numbers of natural killer (NK) cells within the maternal decidua in close proximity to the fetally-derived invading extravillous trophoblast which expresses at least two HLA class I molecules, HLA-G and HLA-C. These NK cells have an unusual phenotype, CD56(bright) CD16, distinguishing them from adult peripheral blood NK cells. They may control key events in trophoblast migration and therefore placentation. Human NK cells in peripheral blood express receptors for polymorphic HLA class I molecules. This family of receptors, known as killer cell inhibitory receptors (KIR), are expressed on overlapping subsets of NK cells to give an NK cell repertoire which differs between individuals. Using a panel of monoclonal antibodies to several members of the KIR family and analysis by flow cytometry, we have found that KIR are expressed by decidual NK cells. There is variation in both the percentage of cells expressing a particular receptor and the density of receptor expression between decidual NK cells from different individuals. Comparison of NK cells from decidua and peripheral blood of the same individual showed that NK cells from these two different locations express different repertoires of KIR. Receptors are present in individuals who do not possess the relevant class I ligand, raising the possibility that these NK receptors may be involved in recognition of the allogeneic fetus by the mother at the implantation site.

Adult↗
PubMed1997

Cytokine production and cytokine receptor expression by cells of the human first trimester placental-uterine interface.

There is currently a great deal of interest in the role that cytokines may play in placental development. A variety of cytokines have been demonstrated at the placental-uterine interface, but the exact cellular sources of production have not yet been identified due to the complex tissue topography of the implantation site. In the present study, we have used the enzyme-linked immunosorbent assay (ELISA) to investigate cytokine production in vitro by cells isolated with a high degree of purity from the placenta and decidua. The cytokines assayed were EGF, interleukin 1 beta (IL-1 beta), IL-2, IL-3, interferon alpha (IFN-alpha), IFN-gamma, tumour necrosis factor alpha (TNF-alpha) and transforming growth factor beta 1 (TGF-beta 1). A necessary starting point in the elucidation of cytokine function is to define those cell populations which express relevant cytokine receptors as this would identify the potential cell targets. For this reason, cytokine receptor expression by placental and uterine cells using immunohistology and flow cytometry has been investigated, those being: IGF-1r, PDGF-r alpha/beta, IL-1rII, IL-6r, IL-7r, IFN-gamma r, TNF-rp80 and endoglin. Taken in conjunction with previously published data on other cytokine receptors, a comprehensive picture can begin to be constructed of the putative cytokine-responding cells present in the human placental-uterine interface.

Cells, Cultured↗
PubMed1997

Human uterine NK cells have a similar repertoire of killer inhibitory and activatory receptors to those found in blood, as demonstrated by RT-PCR and sequencing.

The expression of natural killer (NK) cell receptors specific for HLA class I molecules has been studied in CD56bright, CD3- NK cells isolated from the pregnant uterine mucosa, the decidua. RT-PCR was performed on cDNA from uterine NK cells with primers designed to amplify members of the killer inhibitory receptor (KIR)/killer activatory receptor (KAR) gene family. Sequencing of the PCR products revealed that uterine NK cells express KIR/KAR which have two or three extracellular immunoglobulin superfamily (Ig-SF) domains. NK receptors for both groups of HLA-C alleles were found. KIR, characterised by a long cytoplasmic tail containing the immune receptor tyrosine-based inhibitory motif (ITIM), and KAR, characterised by a short cytoplasmic domain with a transmembrane region containing a charged lysine, were both identified. Different individuals appear to have a distinct but overlapping repertoire of KIR/KAR. No new members of this NK receptor gene family were identified in the uterine CD56bright NK cells. Similar findings were obtained from non-pregnant endometrial tissues representative of different stages of the menstrual cycle. Immunohistology confirmed that the KIR protein products were expressed by decidual NK cells. These results reveal that NK receptors for trophoblast HLA class I molecules are present in maternal uterine NK cells. Fetal trophoblast cells infiltrating the decidua express HLA-G and HLA-C gene products. This suggests that maternal recognition of the fetus may be mediated by an NK allorecognition system.

CD56 Antigen↗
PubMed1997

Immunology of human placental implantation: clinical implications of our current understanding.

In the early 1950s, Medawar proposed the concept of "the fetus as an allograft". Since then, the immunological relationship between the mammalian fetus and its mother during pregnancy has been considered to be similar to that between a transplanted allograft and its recipient. Because of this analogy, it has been assumed that implantation of the fetal placenta in the uterus would similarly be controlled by a maternal immune response mediated by T cells recognizing paternally derived alloantigens expressed by the placenta. Surprisingly, recent evidence suggests that implantation might predominantly involve a novel allogeneic recognition system based on natural killer cells rather than T cells. The cellular and molecular basis of this local immune interaction between the fetal placenta and maternal uterus is now the focus of intense research interest. Because aberrant implantation can cause a variety of clinical problems including miscarriage, intrauterine growth retardation and pre-eclampsia, an understanding of the immunological mechanism by which this process is controlled could lead to the development of regimes to treat these important obstetric conditions.

Female↗
PubMed1997

Lymphocytes of human term decidua decrease cell adhesion to a plastic substrate.

Although human decidual lymphocytes have been widely studied, their function and possible interaction with trophoblast are still unclear. Here we show that whereas human early (EDL) and term (TDL) decidual lymphocytes were unable to kill human trophoblast by necrosis (assessed by the 51Cr-release assay) or apoptosis (DNA fragment assay), TDL but not EDL decreased trophoblast adhesion to a plastic substrate as determined by a [3H]thymidine assay. This effect, however, was not selective for trophoblast, as TDL also decreased the adhesion to plastic of human decidual stromal cells and HeLa cells. Our results suggest that TDL may play a role in placental detachment during parturition by decreasing trophoblast or decidual stromal cell adhesion.

Apoptosis↗
PubMed1997

Evaluation of trophoblast HLA-G antigen with a specific monoclonal antibody.

A monoclonal antibody to HLA-G has been generated by immunizing HLA-A2.1/human beta 2-microglobulin (beta 2 m) double transgenic mice with murine L cells transfected with both human beta 2 m and HLA-G. This monoclonal antibody, designated as G233, has been found not to cross-react with other HLA class I antigens when tested on numerous cell lines by flow cytometry. With immunohistology, all populations of extravillous trophoblast (cell columns, interstitial trophoblast, endovascular trophoblast, placental bed giant cells) were stained. An extensive range of adult and fetal tissues was also tested but none reacted with monoclonal antibody G233, including those previously reported to express HLA-G mRNA, indicating that the protein has a highly restricted distribution. Failure to detect HLA-G in the fetal thymus raises the question as to how T-cell tolerance to this antigen is induced. Immunoprecipitation of trophoblast surface proteins with monoclonal antibody G233 revealed a heavy chain of 39 kDa and a light chain of 12 kDa, indicating that HLA-G expressed on the surface of trophoblast is complexed with beta 2 m. However, sequential immunoprecipitation with monoclonal antibody W6/32 followed by monoclonal antibody G233 continued to detect a residual band of 39 kDa, suggesting that trophoblast surface HLA-G may also occur as free heavy chains not associated with beta 2 m. Immunoprecipitation followed by two dimensional gel electrophoresis showed that monoclonal antibody G233 recognizes several isoforms of HLA-G from trophoblast similar to the characteristic spot array previously described for HLA-G. This monoclonal antibody G233 will be highly useful in future experiments to elucidate the function of HLA-G.

Adult↗
PubMed1997

Uterine NK cells and trophoblast HLA class I molecules.

PROBLEM: To investigate the proposal that NK cells in decidua may control trophoblast migration during implantation of the human placenta. METHOD: Use Mab specific for HLA-G and for HLA-C in association with flow cytometry and immunoprecipitation to determine the expression of these HLA molecules by trophoblast. Expression of Killer inhibitory/activatory receptors (KIR/KAR) and the CD94 receptor by decidual NK cells was also studied. RESULTS: Extravillous trophoblast expressed HLA-G and HLA-C in both beta2m-associated form and as free heavy chains. KIR and KAR are expressed by decidual NK cells. The repertoire of receptors varied between different women and also between blood and decidual NK cells from the same women. The expression of CD94 was also different between blood and decidual NK cells. CONCLUSION: The recognition of HLA-G/HLA-C by KIR/KAR and CD94 could provide a mechanism by which decidual NK cells control trophoblast migration.

Antibodies, Monoclonal↗