Cellular immune recognition of HLA-G-expressing choriocarcinoma cell line Jeg-3

Integrated microRNA and secretome analysis of human endometrial organoids reveal the miR-3194-5p/Aquaporin/S100A9 module in regulating trophoblast functions

Successful placentation requires delicate communication between the endometrium and trophoblasts. The invasion and integration of trophoblasts into the endometrium during early pregnancy is crucial to placentation. Dysregulation of these functions is associated with various pregnancy complications, such as miscarriage and preeclampsia. The endometrial microenvironment has an important influence on trophoblast cell functions. The precise effect of the endometrial gland secretome on trophoblast functions remains uncertain. We hypothesized that the hormonal environment regulates the miRNA profile and secretome of the human endometrial gland, which subsequently modulates trophoblast functions during early pregnancy. Human endometrial tissues were obtained from endometrial biopsies with written consent. Endometrial organoids were established in matrix gel under defined culture conditions. They were treated with hormones mimicking the environment of the proliferative phase (Estrogen, E2), secretory phase (E2+Progesterone, P4), and early pregnancy (E2+P4+Human Chorionic Gonadotropin, hCG). miRNA-seq was performed on the treated organoids. Organoid secretions were also collected for mass spectrometric analysis. The viability and invasion/migration of the trophoblasts after treatment with the organoid secretome were determined by cytotoxicity assay and transwell assay, respectively. Endometrial organoids with the ability to respond to sex steroid hormones were successfully developed from human endometrial glands. By establishing the first secretome profiles and miRNA atlas of these endometrial organoids to the hormonal changes followed by trophoblast functional assays, we demonstrated that sex steroid hormones modulate aquaporin (AQP)1/9 and S100A9 secretions through miR-3194 activation in endometrial epithelial cells, which in turn enhanced trophoblast migration and invasion during early pregnancy. By using a human endometrial organoid model, we demonstrated for the first time that the hormonal regulation of the endometrial gland secretome is crucial to regulating the functions of human trophoblasts during early pregnancy. The study provides the basis for understanding the regulation of early placental development in humans.

Experimental human placental models for studying uptake, transport and toxicity of micro- and nanoplastics

Micro- and nanoplastics (MNPs) are ubiquitous in the environment and have recently been found in human lungs, blood and placenta. However, data on the possible effects of MNPs on human health is extremely scarce. The potential toxicity of MNPs during pregnancy, a period of increased susceptibility to environmental insults, is of particular concern. The placenta provides a unique interface between maternal and fetal circulation which is essential for in utero survival and healthy pregnancy. Placental toxicokinetics and toxicity of MNPs are still largely unexplored and the limited studies performed up to now focus mainly on polystyrene particles. Practical and ethical considerations limit research options in humans, and extrapolation from animal studies is challenging due to marked differences between species. Nevertheless, diverse in vitro and ex vivo human placental models exist e.g., plasma membrane vesicles, mono-culture and co-culture of placental cells, placenta-on-a-chip, villous tissue explants, and placental perfusion that can be used to advance this research area. The objective of this concise review is to recapitulate different human placental models, summarize the current understanding of placental uptake, transport and toxicity of MNPs and define knowledge gaps. Moreover, we provide perspectives for future research urgently needed to assess the potential hazards and risks of MNP exposure to maternal and fetal health.

Isolation of HLA-G+ cells using MEM-G/9 antibody-conjugated magnetic nanoparticles for prenatal screening: a reliable, fast and efficient method

The development of an effective and noninvasive early method for obtaining fetal cells is crucial to prenatal screening. Despite proving the presence of fetal cells in the reproductive tract, their use is limited due to their inability to properly isolate them from maternal cells. Magnetic-activated cell sorting (MACS) is a simple technique to separate cells. The present study aimed to develop a MACS-based platform for the isolation of the HLA-G expressing trophoblast cells. For this purpose, first, the triazine functionalized MNPs were synthesized and characterized. Then, MNPs were directly and indirectly conjugated by the MEM-G/9 antibodies targeting HLA-G+ cells. The antibody amount on the surface of the nanoparticles was determined with the Bradford assay. The cell capture efficiency was also investigated. Various characterization methods confirmed the successful nanoparticle synthesis and antibody conjugation. The optimal initial antibody amount for the immobilization was about 20 μg and the optimal time was 3 h. The antibody-nanoparticles by the indirect method had better targeting and capture efficiency than the direct method. The MNPs indirectly conjugated with antibodies are an efficient tool for cell isolation and present considerable potential to be applied in biomedical fields.

Appropriate fixative for MEM-G/9 staining of cultured human HLA-G-positive JEG-3 trophoblast tumor cells

Human leukocyte antigen (HLA-G) participates in immunosuppression and is useful for prenatal diagnostics. Isolation of fetal cells positive for HLA-G by HLA-G antibody conjugated nanoparticles from the cervix of pregnant women is the basis for non-invasive prenatal testing. Endocervical specimens are fixed in transport medium before isolation using antibody conjugated nanoparticles. Staining of HLA-G using MEM-G/9 antibody, however, is restricted to unfixed cells. We investigated the effect of several fixatives on the interaction of HLA-G with MEM-G/9 in the HLA-G-positive cell line, JEG-3. We investigated absolute methanol, 1:1 acetate buffer:methanol, Pap solution and paraformaldehyde. The effects of these fixatives were evaluated using immunofluorescence. We found no MEM-G/9 surface staining of methanol fixed cells. Approximately 40% of JEG-3 cells fixed with paraformaldehyde failed to stain. Nearly all cells were stained with MEM-G/9 following fixation with acetate buffer:methanol or Pap solution. Our findings indicate the importance of using an appropriate fixative for preserving HLA-G cell surface antigen for studies using the MEM-G/9 antibody.

Anti α-enolase antibody is a novel autoimmune biomarker for unexplained recurrent miscarriages

Background

We recently demonstrated the increased abundance of anti-trophoblast antibodies (ATAB) in sera of patients with unexplained recurrent miscarriages (uRM). Further, the ATAB-positive sera bound to JEG-3 human choriocarcinoma cells in vitro, resulting in decreased productions of β-human chorionic gonadotropin (β-hCG) and progesterone in these cells. However, the specific antigenic epitopes of ATAB have remained unknown. Therefore, it was the aim of this study to determine specific targets of ATAB in uRM patients.

Methods

Potential targets of ATAB were analyzed by 2-dimensional difference gel electrophoresis (2D-DIGE) and mass spectrometry, and thereby identifying α-Enolase (ENO1). ATAB targeting of ENO1 was further confirmed in a competitive binding assay. Levels of anti-ENO1 antibodies as well as β-hCG and progesterone were quantified with enzyme-linked immunosorbent assay (ELISA). Additionally, expression of ENO1 was analyzed in first trimester placentas by immunohistochemistry and immunofluorescence analysis.

Findings

We here identified ENO1 as a prominent target of ATAB. Serum levels of anti-ENO1 antibodies were increased in ATAB-positive compared to ATAB-negative patients. Further, increased expression of ENO1 and its co-expression with β-arrestin was found in the extra villous trophoblasts of uRM patients in first trimester placentas. In vitro, anti-ENO1 antibodies decreased the secretion of β-hCG and progesterone in JEG-3 and primary human villous trophoblast cells.

Interpretation

Serum anti-ENO1 antibodies might be an autoimmune biomarker for uRM. Targeting the formation of anti-ENO1 antibodies or inhibition of ENO1 expression could potentially represent therapeutic strategies for these patients.

Fund

All authors declare no conflict of interest. Yao Ye was supported by the China Scholarship Council. Hellen Ishikawa-Ankerhold and Christian Schulz were supported by the SFB914, projects Z01 and A10. None of the rest authors has any conflict of interest to declare.

Effects of polyvalent immunoglobulins in patients with recurrent pregnancy loss and antibodies to the choriocarcinoma cell line JEG-3

OBJECTIVE

The benefit of polyvalent immunoglobulins (IVIG) for patients with recurrent pregnancy loss (RPL) is controversially discussed. Anti-trophoblast antibodies as an expression of immune pathology have been associated with RPL. We investigated whether the antibody activity against the choriocarcinoma cell line JEG-3 in RPL patients is influenced in vitro by IVIG.

STUDY DESIGN

Sera of 110 unexplained RPL patients with positive anti-JEG-3 antibodies were coincubated with IVIG in different concentrations (10mg/ml, 20mg/ml, 40mg/ml). Coincubation with human albumin in identical concentrations served as control. Anti-JEG-3 reactivity was measured by using flow cytometry in comparisons with two in-house standards antibody probes of low and high reactivity as described before. Anti-JEG-3 reactivity above the 95% confidence interval of controls was defined as positive.

RESULTS

Incubating RPL sera with 10mg/ml IVIG significantly decreased anti-JEG-3 activity (p<0.001). Increasing IVIG concentration to 40mg/ml resulted in a slightly additionally reduction (p=0.42). In contrast, coincubation with albumin in identically concentrations did not affect anti-JEG-3 activity (p>0.40).

CONCLUSION

Coincubation with IVIG in vitro leads to a significant suppression of anti-JEG-3 activity in the sera of RPL patients.

Human Parthenogenetic Embryonic Stem Cell-Derived Neural Stem Cells Express HLA-G and Show Unique Resistance to NK Cell-Mediated Killing

Parent-of-origin imprints have been implicated in the regulation of neural differentiation and brain development. Previously we have shown that, despite the lack of a paternal genome, human parthenogenetic (PG) embryonic stem cells (hESCs) can form proliferating neural stem cells (NSCs) that are capable of differentiation into physiologically functional neurons while maintaining allele-specific expression of imprinted genes. Since biparental ("normal") hESC-derived NSCs (N NSCs) are targeted by immune cells, we characterized the immunogenicity of PG NSCs. Flow cytometry and immunocytochemistry revealed that both N NSCs and PG NSCs exhibited surface expression of human leukocyte antigen (HLA) class I but not HLA-DR molecules. Functional analyses using an in vitro mixed lymphocyte reaction assay resulted in less proliferation of peripheral blood mononuclear cells (PBMC) with PG compared with N NSCs. In addition, natural killer (NK) cells cytolyzed PG less than N NSCs. At a molecular level, expression analyses of immune regulatory factors revealed higher HLA-G levels in PG compared with N NSCs. In line with this finding, MIR152, which represses HLA-G expression, is less transcribed in PG compared with N cells. Blockage of HLA-G receptors ILT2 and KIR2DL4 on natural killer cell leukemia (NKL) cells increased cytolysis of PG NSCs. Together this indicates that PG NSCs have unique immunological properties due to elevated HLA-G expression.

Characterization of human umbilical cord lining-derived epithelial cells and transplantation potential

In this study we describe the derivation and immunological characterization of a primary epithelial cell type from the human umbilical cord membrane. These cord lining epithelial cells (CLECs) expressed and/or secreted isoforms of the nonclassical human leukocyte antigen class I (HLA-1b) glycoproteins, HLA-G and E. Conditioned media from CLECs inhibited mitogen-stimulated T-lymphocyte responses, and in a mixed leukocyte reaction (MLR) assay, cocultured CLECs inhibited allogeneic responses with a concomitant reduction in proinflammatory cytokines. Using a transwell coculture system, it was demonstrated that these immunoregulatory effects were mediated by soluble factors secreted by CLECs, in a dose-dependent manner. Functional studies using HLA-G blocking antibody showed that the effects of CLEC-secreted products could be inhibited, thus demonstrating a significant and important role for soluble HLA-G. In vivo, we show that transplanted CLECs could be maintained for extended periods in immunocompetent mice where xenorejection rapidly destroyed primary keratinocytes, a control human epithelial cell type. Additionally, CLECs delayed the rejection of keratinocytes and extended their survival when cotransplanted, indicating an ability to protect adjacent human cell types that would otherwise be rejected if transplanted alone. We also show that CLECs transduced with a modified human proinsulin gene were transplanted intraperitoneally into streptozotocin (STZ)-induced diabetic mice, resulting in significantly lower levels of serum glucose compared to control mice. This study has characterized the immunological properties of CLECs and tested a potential therapeutic application in the treatment of a type 1 diabetes mouse model.

Production and Characterization of Monoclonal Antibodies with Specificity for Human HLA-G Isoforms

Production of monoclonal antibodies to HLA-G, a nonpolymorphic antigen of non-classical HLA class I, is of basic and clinical importance. In the present study, monoclonal antibodies were prepared which recognize different membrane bound and soluble isoforms of HLA-G, following immunization of BALB/c mice with a synthetic peptide. Use of this peptide (23 residues), which is present in the alpha1 domain of HLA-G, was previously demonstrated to provide antibodies useful for recognition of HLA-G isoforms in human placenta. Antibody-producing hybridomas were screened by an indirect one-step ELISA method. A clone designated 5E6H7, secreted antibodies useful in immunostaining studies involving both surface HLA-G of placental tissues and soluble forms of this antigen in human sera. In addition, unreactivity of this antibody with human lymphocytes and sections of normal human skin was observed by immunofluorescence microscopy, thus demonstrating its specificity for HLA-G.

MICA triggering signal for NK cell tumor lysis is counteracted by HLA-G1-mediated inhibitory signal

MICA, a highly glycosylated membrane-anchored cell-surface MHC Class I-related chain, has recently been reported to activate NK cell cytolytic responses in epithelial tumors. Tumor cells may escape from NK lysis by counteracting NK cytotoxicity activating signals with inhibitory ones. Among the molecules that mediate an NK inhibitory signal, HLA-G1, a non-classical MHC Class I antigen, is of particular interest. HLA-G1 is ectopically expressed in various tumors, including melanoma and constitutes the major NK inhibitory ligand in the M8 melanoma cell line when coexpressed with HLA-A, -B, -C and -E molecules. We have evaluated the balance between 2 powerful signals that affect NK cell tumor lysis, one inhibitory and the other one activating, respectively HLA-G1 and MICA. For this purpose, we transfected the M8 melanoma cell line, which spontaneously expresses MICA, with HLA-G1 cDNA, using it as a target for the NKL effector. We carried out cytotoxicity assays, using antibodies that disrupt interactions between the MICA and HLA-G1 ligands and their respective NK effector counterparts, the NKG2D activating and ILT2 inhibitory receptors. Results showed that 1) MICA expressed in the M8 melanoma cell line triggered NK cell tumor lysis and 2) HLA-G1 coexpression mediated the inhibition of NK cytotoxicity by mitigating the MICA activating signal. HLA-G1 expression in a tumor cell line in which MICA is switched on would therefore appear to be a powerful way to turn off NK cells, supporting the emerging idea that the balance between positive and negative NK cytolysis signals critically influences tumor progression.

HLA-G suppresses proliferation of CD4(+) T-lymphocytes

HLA-G is a non-classical MHC class 1 molecule, expressed primarily on human foetal trophoblast cells, which exhibits almost no genetic polymorphism. Because of these unusual features, HLA-G has been suggested to help prevent maternal immune attack of the semi-allogeneic foetus. The aim of these experiments was to investigate the effects of HLA-G on T-lymphocyte responses by using MHC class II-bearing HLA-G transfectants as stimulators of a mixed lymphocyte reaction. The presence of HLA-G, but not classical HLA class I, on the surface of stimulator cells markedly suppressed thymidine incorporation by peripheral blood mononuclear responder cells from a class I-similar, class II-dissimilar male. The suppressive effect of HLA-G on the mixed lymphocyte reaction persisted after depletion of phagocytes and CD8(+) T-cells from the responder population, but the mixed lymphocyte reaction was entirely abolished by depletion of CD4(+) T-cells. These results suggest that HLA-G exerts a direct suppressive effect on CD4(+) T-lymphocytes, even in the absence of the CD8(+) cells with which other human MHC class I molecules are thought to interact. Thus, HLA-G may allow the foetus to escape maternal immune attack by modulating CD4(+) T-cell activity.

Differential expression of major histocompatibility complex class Ia, Ib, and II molecules on monocytes-derived dendritic and macrophagic cells

Blood monocyte derived antigen presenting cells (APC) such as dendritic cells and macrophages are considered as major promising tools for antitumoral immunotherapy. In order to contribute to their phenotype characterization, we have precisely investigated their levels of expression of MHC class Ia, Ib (HLA-G) and II molecules using mainly flow cytometry quantification assays. APC were generated from monocytes cultured for 7 days in the presence of GM-CSF and IL-4 or M-CSF. These cells, which exhibited known morphological and immunological features of dendritic cells and macrophages respectively, were evidenced to display high expression of MHC class Ia and class II antigens in comparison to that found in monocytes. Dendritic cells and macrophages thus expressed 2-fold more and 4-fold more MHC class Ia molecules and 5-fold and 3-fold more MHC class II DR molecules than parental monocytes. In addition, expression of MHC class II DP and DQ molecules, not or only barely detected in monocytes, was clearly demonstrated in the two kinds of APC. In contrast, monocytes, dendritic cells and macrophages failed to express MHC class Ib HLA-G antigen. The up-regulation in monocyte-derived APC of MHC class Ia and II molecules mediating the presentation of antigen peptides to lymphocytes fully supports the interest of such APC in antitumoral immunotherapy.

HLA-G inhibits the allogeneic proliferative response

HLA-G is a non-classical MHC class I molecule expressed at the feto/maternal interface where it plays a role in materno-fetal tolerance by inhibiting NK cells. Expression of killing inhibitory receptors capable of interacting with HLA-G on T lymphocytes led us to hypothesize that HLA-G molecules could also modulate T cell responses, analyzed here in the context of the allogeneic proliferative response. Using LCL-HLA-G transfectants as stimulators of T cells present among peripheral mononuclear cells and K562-HLA-G1 transfectants as inhibitors in a classical mixed lymphocyte reaction, we showed that HLA-G is able to inhibit T cell allo-proliferation. These findings provide new insight into the role of HLA-G in preventing allograft rejection.

Interleukin-12 augments cytolytic activity of peripheral and decidual lymphocytes against choriocarcinoma cell lines and primary culture human placental trophoblasts

PROBLEM

Human trophoblasts are tolerant to the maternal immune system, but susceptible to interleukin (IL)-2-activated lymphocytes. IL-12 is also a key cytokine in the induction of cytotoxic responses. We administered IL-12 to peripheral blood lymphocytes (PBLs) and to decidual lymphocytes (DLs) and studied resulting cytotoxicity against trophoblasts.

METHOD OF STUDY

PBLs and DLs were stimulated with rIL-2 and/or rIL-12 for 48 hr in vitro. Cytotoxicity against the choriocarcinoma cell line JEG-3, JAR, and primary culture trophoblasts were examined by LDH release assay. The proliferative response was estimated by MTT assay. Expression of cytotoxic factors was studied by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Whereas IL-12 alone produced a modest enhancement in cytotoxicity of PBLs and DLs, the combination of IL-2 and IL-12 was most effective in trophoblast cell lysis. IL-12 enhanced the mRNA expression of T-cell specific serine protease (TSP, granzyme B) and FasL in DLs, but the expression of perforin was unchanged. Expression of these cytotoxic factors in PBLs was up-regulated by IL-12.

CONCLUSION

Our findings indicate critical roles of IL-12 in the activation of maternal lymphocytes, which could possibly result in pregnancy failure syndromes.

Detection of soluble HLA-G molecules in plasma and amniotic fluid

Although the cDNA sequence of HLA-G antigens is compatible with their expression as soluble molecules (sHLA-G), the determination of native sHLA-G levels in body fluids has not yet been described. The lack of this information is likely to reflect the difficulties in developing an assay suitable to measure sHLA-G antigens in the presence of soluble HLA-A, -B and -C (sHLA-I) antigens, since most of the available anti-HLA-G mAb do not detect soluble beta2-m associated HLA-G antigens or crossreact with sHLA-I antigens. Therefore, we have developed a two-step assay which eliminates the interference of classical HLA class I antigens. In the first step, the sample is depleted of sHLA-I antigens and of HLA-E antigens with mAb TP25.99. Then, HLA-G antigens are captured with mAb W6/32 and detected with anti-beta2-m mAb in ELISA. Utilizing this assay, sHLA-G antigen levels were measured in EDTA plasma from 92 controls with known HLA types, 28 women at delivery and the corresponding cord bloods and in 50 amniotic fluids. Mean sHLA-G plasma levels did not differ between males (24.9+/-3.0 SEM ng/ml; n=42) and females (20.1+/-2.1 SEM ng/ml; n = 50). However, sHLA-G levels in HLA-A11 positive probands (mean: 13.0+/-4.4 SEM ng/ml; n=12) were significantly (P<0.05) lower than in HLA-A11 negative ones (mean: 24.5+/-2.0 SEM ng/ml; n=80). sHLA-G levels in women at delivery (mean: 22.9+/-2.2 SEM ng/ml; n=28) were in the range of controls but were significantly (P<0.001) reduced in the corresponding cord bloods (mean: 13.8+/-1.5 SEM ng/ml; n=28). sHLA-G levels in amniotic fluids (mean: 15.5 + 1.0 SEM ng/ml; n=50) were significantly (P<0.001) lower than in plasma. sHLA-G levels were 5 and 11% of those of sHLA-I antigens in plasmas and amniotic fluids, respectively. Individual sHLA-G levels were not correlated with sHLA-I levels. SDS-PAGE analysis of plasma sHLA-G antigens revealed two molecular variants with a 35 kD and a 27 kD MW corresponding to the sizes of sHLA-G1 and -G2 isoforms. In conclusion, our study has shown that the two-step assay we have developed is reliable in measuring sHLA-G antigen levels. This assay will facilitate the analysis of the biological and clinical significance of sHLA-G antigens in plasma.

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.

Cytotoxic T lymphocyte recognition of HLA-G in mice

Several features of HLA-G's sequence and expression pattern distinguish HLA-G from its classical counterparts. These features, including HLA-G's limited polymorphism and its expression at the maternal-fetal interface, have been used as a basis for suggesting a distinct functional role for this nonclassical class I HLA molecule. On the other hand, published data do demonstrate that HLA-G has much in common with its classical counterparts. It associates with beta 2-microglobulin and cytosolic peptides, it binds to CD8, and its presence can inhibit NK-cell-mediated lysis of HLA-G-bearing target cells. To develop a model in which HLA-G's function could be more thoroughly studied, we produced several HLA-G-expressing transgenic mouse strains. We report here the results of skin graft experiments which show that nontransgenic mice reject HLA-G-expressing transgenic murine skin as foreign and that this rejection is associated with the presence in the recipient of lymphocytes capable of specifically lysing HLA-G-expressing cells. In addition, experiments are described which demonstrate that HLA-G transgenic mice recognize HLA-G as a "self" molecule. Together the reported data demonstrate that HLA-G is capable of stimulating an HLA-G-restricted CTL response, that HLA-G molecules can serve as target molecules in lytic interactions with CTLs, and that HLA-G is involved in education of the lymphocytic repertoire of HLA-G transgenic mice.

Human decidual leukocytes do not proliferate in response to either extravillous trophoblast or allogeneic peripheral blood lymphocytes

The maternal leukocytes present in human decidua during the early weeks of pregnancy are composed of CD56+ NK cells (approximately 80%), CD3+ T cells (approximately 10%), and CD14+ macrophages (approximately 10%). These leukocytes are present in large numbers at the implantation site where trophoblast invades. The migrating extravillous trophoblast (EVT) cells express HLA class I antigens HLA-G and HLA-C. To examine whether EVT or other allogeneic cells are capable of inducing a local proliferative response in maternal decidual leukocytes, we have assayed [3H]thymidine incorporation by decidual leukocytes co-cultured with irradiated trophoblast or peripheral blood lymphocytes (PBL). No proliferative response was seen in decidual leukocytes either to trophoblast or to PBL as stimulators. In addition trophoblast did not stimulate a proliferative response in PBL. These findings indicate that extravillous trophoblast is not capable of initiating a classical immune response at the implantation site.

Soluble HLA-G molecule. An alternatively spliced HLA-G mRNA form candidate to encode it in peripheral blood mononuclear cells and human trophoblasts

The HLA-G nonclassic MHC class I gene expressed at the maternal-fetal interface may be involved in cell protection against NK cell lysis. HLA-G mRNA is observed in different adult or fetal human cells and exhibits four alternative forms: HLA-G1, HLA-G2, HLA-G3, and HLA-G4 lacking, respectively, exon 7; exons 7 and 3, exons 7, 3, and 4; exons 7 and 4. Because exon 5 encodes the transmembrane domain of the HLA-G antigen, none of these transcripts could give a soluble form as detected in supernatant of trophoblasts. In this report, we describe an additional alternatively spliced for of HLA-G transcript (HLA-G5) present in adult PBMCs and first-trimester trophoblasts that contains intron 4. Moreover, as with all other transcripts, HLA-G5, is devoid of exon 7. Its relative frequency is, respectively, approximately 1:8 and approximately 1:26 in adult PBMCs and first-trimester trophoblasts. The presence of intron 4 generates a stop codon that excludes transmembrane region (exon 5) of the HLA-G molecule and therefore might produce a soluble antigen. These results are discussed with regard to data on soluble forms of classic HLA antigens and the possible role of HLA-G.

An alternatively spliced form of HLA-G mRNA in human trophoblasts and evidence for the presence of HLA-G transcript in adult lymphocytes

The HLA-G monomorphic, nonclassical class I gene encodes the major histocompatibility complex (MHC) molecule, which is the only MHC antigen expressed on cytotrophoblast cells of placenta. In this work, we have investigated expression of the HLA-G gene in fetal tissues and adult peripheral blood cells by using a sensitive hot-start reverse transcriptase PCR technique. PCR amplification with HLA-G primers specific for exon 3 has enabled us to demonstrate an alternatively spliced form of HLA-G mRNA present in fetal first trimester trophoblasts and lacking exon 4 (HLA-G.3-5). This low abundance transcript (approximately 1:200) in comparison to full-length mRNA may encode the protein that excludes the alpha 3 domain and by conformational changes may present a different ability to bind to peptides. Moreover, expression of the HLA-G transcript was found in adult peripheral lymphocytes and equally in B- and T-cell populations. These results are discussed in the context of the fetal-maternal relationship presented by HLA-G gene products.

Immunobiology of pregnancy

This report presents new findings on two conditions that permit genetically disparate tissues to coexist during pregnancy: (a) regulation of major histocompatibility genes in placental trophoblast, and (b) synthesis of uterine and placental polypeptide growth factors with immunosuppressive properties. Recent experiments examining inter-relationships between these two protective mechanisms are cited, and potential explanations for trophoblast resistance to factors with MHC-inducing properties are proposed.

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.