Macrophages in the uterus and placenta.
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Animals↗
Biomedical subjects
J S Hunt
Publications and source records attributed to J S Hunt.
Differential distribution of interleukin-1 alpha and interleukin-1 beta proteins in human placentas.
Interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta) were identified in samples of first trimester and term placentas by immunocytochemistry using two sets of polyclonal antibodies to recombinant IL-1. All samples contained the two species of IL-1, which predominated in different types of cells: IL-1 alpha was contained primarily in placental villous trophoblastic and stromal cells whereas IL-1 beta was localized to cells in fetal and maternal blood. With respect to the cellular localization of the two proteins, early and late gestation tissues were similar. Although these results were generally consistent for the two sets of antibodies, differences were noted in the binding patterns of the individual reagents. The findings in this study provide strong support for the postulate that IL-1 modulates placental development and suggest that IL-1 alpha may be the preferred species in extraembryonic tissues.
Blood Cells↗
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.
Animals↗
Tumor necrosis factor-alpha gene expression in the tissues of normal mice.
Although TNF-alpha is traditionally associated with macrophage activation during neoplasia and acute inflammation, recent Northern blot hybridization studies indicate that gene expression occurs in the absence of pathology. In order to identify the cellular sources of endogenous message and protein, normal mouse tissues were tested for TNF-alpha mRNA using in situ hybridization and for the corresponding protein by immunocytochemistry. Unexpectedly, specific TNF-alpha message was readily detected in hepatocytes, kidney tubule epithelial cells, various populations of spleen cells and neurons. TNF-alpha protein was present in the same liver and kidney cells as those that contained TNF-alpha mRNA, was low in spleen cells, and was absent in neurons. These results suggest that cells other than macrophages are the major sources of TNF-alpha gene products in normal tissues, indicate that regulation is accomplished by more than one mechanism, and are consistent with the postulate that products of this gene contribute to normal physiological processes.
Animals↗
Tumor necrosis factor-alpha messenger ribonucleic acid and protein in human endometrium.
Although previous studies have shown that the tumor necrosis factor-alpha (TNF) gene is expressed in pregnancy decidua, it has not been determined whether this gene is transcribed or translated in the endometrium prior to implantation. To address this question and to identify cells expressing the TNF gene, samples of normal cycling human endometria were tested for TNF mRNA by in situ hybridization using a biotinylated antisense RNA probe, and the corresponding protein was localized in the same tissues by immunocytochemistry with a monoclonal antibody to TNF. Both TNF message and protein were identified in the endometrium throughout the menstrual cycle, and the same types of cells that contained transcripts also contained protein. As judged by the intensities of the hybridization signals, TNF mRNA increased during the proliferative phases, declined in the early secretory phase, and again rose during mid-to-late secretory phases, suggesting positive associations with levels of female sex hormones that show similar cyclic fluctuations. At the initiation of the cycle, transcripts were primarily localized to glandular epithelial cells whereas by the midproliferative phase, message was also present in stromal cells. Hybridization signals were consistently more intense in functionalis-region than in basalis-region stromal cells, and were frequently stronger in basalis-region glandular epithelia than in functionalis-region glands. These observations document that the TNF gene is expressed in normal cycling endometria, suggest that ovarian hormones may regulate TNF gene transcription, and identify differences in specific endometrial compartments. The findings are also consistent with the postulate that TNF is a local mediator of cellular communications in the human endometrium.
Adult↗
HLA and maternal-fetal recognition.
Despite genetic differences, mothers do not reject their semiallogeneic embryos. Regulated expression of the major histocompatibility antigens (HLA) by placental trophoblast cells, which intervene between the embryo and maternal blood and tissues, is now believed to play an important role in this surprising feature of pregnancy. Transcription and translation of the highly polymorphic class I HLA-A, -B, -C genes whose products stimulate graft rejection are blocked in trophoblast cells. Instead, these cells express HLA-G, a nonpolymorphic gene. Moreover, the cells do not express class II HLA-D antigens, and factors such as interferons that usually enhance HLA expression have no effect on trophoblast cells in situ. Thus, multiple regulatory mechanisms prevent the cells that sequester the embryo from the mother from expressing the potentially deleterious paternal HLA antigens, immunological rejection is avoided and successful pregnancy ensues.
Animals↗
Tumor necrosis factor-alpha mRNA and protein in rat uterine and placental cells.
The pregnant uterus contains TNF-alpha, a potent cytokine with pleotrophic effects. The uterus also contains numerous macrophages, which are well described sources of TNF-alpha. In order to determine if uterine TNF-alpha originated with these macrophages, patterns of macrophage tissue distribution and population densities were first established in rat uterine tissues from early, mid, and late stages of gestation by immunohistology. The potential of these and other uterine and placental cells to synthesize TNF-alpha was then tested by in situ hybridization with the use of biotinylated antisense and sense RNA probes. Although TNF-alpha mRNA was present during all stages of pregnancy, hybridization signals were highest in gestation day 15 tissues. The predominant TNF-alpha mRNA-containing cells were uterine epithelium, decidual cells, and placental trophoblast cells; these cells also contained immunoreactive TNF. Transcription of the TNF gene in the uterus and placenta was also documented by Northern blotting experiments, which showed that the transcript sizes for uterine, placental, and macrophage TNF mRNA were similar. Although stromal cells that were located in macrophage-rich uterine compartments (myometrium, metrial gland) contained TNF-alpha mRNA, the cells did not contain high levels of immunoreactive TNF-alpha. Thus, cells other than macrophages are likely to be the major contributors of TNF-alpha during uncomplicated pregnancy in the rat.
Animals↗
Analysis of HLA-G mRNA in human placental and extraplacental membrane cells by in situ hybridization.
Trophoblast cells arising from the implanted blastocyst form the fetal component of the maternal-fetal interface throughout pregnancy. Previous in situ hybridization studies have shown that some subpopulations of these cells, cytotrophoblast cells within and exterior to placental villi, contain class I HLA mRNA. Those studies, performed under moderate conditions of stringency, did not determine which member(s) of the class I HLA gene family was transcribed. In this study, in situ hybridization experiments were conducted under conditions of high stringency using biotinylated antisense and sense RNA probes specific for HLA-G and HLA-E. HLA-G mRNA was identified in first trimester cytotrophoblast cells and in term chorionic membrane cytotrophoblast cells, but was low to undetectable in syncytiotrophoblast of both early and late gestation placentas. Placental villous mesenchymal cells in first trimester but not term placentas contained HLA-G transcripts. HLA-E mRNA was clearly identified only in small round cells present in first trimester decidua and term membranes. These experiments provide the first direct evidence for transcription of the HLA-G gene by cytotrophoblast cells in situ. Expression of this nonpolymorphic gene in place of HLA-A,B,C by trophoblast cells exposed to maternal blood and tissues may allow the juxtaposition of genetically disparate cells required for human pregnancy.
Female↗
A pregnancy defect in the osteopetrotic (op/op) mouse demonstrates the requirement for CSF-1 in female fertility.
Correlative evidence suggests that maternal production of the mononuclear phagocyte growth factor colony stimulating factor-1 (CSF-1) regulates placental development. In order to study the role of CSF-1 in pregnancy the fertility of CSF-1-less osteopetrotic (op/op) mutant mice was investigated. Homozygous mutant crosses (op/op x op/op) were consistently infertile. As expected, op/op males were almost completely fertile when crossed with heterozygous females. Surprisingly, op/op females when mated to heterozygote males were fertile, although at a rate that was 46% of the rate for +/op females x op/op males. These data suggest that CSF-1 is required for pregnancy. However, a maternal CSF-1 source is not absolutely necessary in that pregnancies involving +/op fathers were partially rescued, suggesting that +/op fetuses and/or +/op seminal fluid provides CSF-1 or CSF-1-induced factors which compensate for the absence of maternally produced CSF-1. Despite the complete absence of CSF-1 in the uterus and placenta of op/op mice placental weights were normal, suggesting that proliferation of decidual cells and trophoblasts, both of which express the CSF-1 receptor, may not be solely regulated by CSF-1. Histochemical staining for F4/80 antigen was used to identify macrophages in the uterus and placenta. Uterine macrophages could not be detected in virgin op/op mice although they were abundant in +/op uteri. Interestingly, macrophages could be detected in op/op uteri as uncharacteristically rounded cells in early gestation, however, they were not maintained and no macrophages were apparent beyond Day 14 of pregnancy in op/op mice. Further studies in the osteopetrotic mouse will be useful in delineating those functions required for pregnancy that are regulated by CSF-1.
Animals↗
Differential expression of complement regulatory proteins on subpopulations of human trophoblast cells.
Trophoblast cells forming the reactive interface between the mother and her semiallogeneic fetus risk attack by cellular and humoral elements of the maternal immune system. Biochemical, molecular, and immunohistologic studies have identified membrane cofactor protein (MCP) and decay accelerating factor (DAF) on trophoblast cells, which could assist in preventing lysis of the cells by complement-activating maternal antibodies. In this immunocytochemical study, differential expression of these two members of the family of complement regulatory proteins on subpopulations of human trophoblast cells and other types of cells in first and third trimester placentas was demonstrated. Staining with anti-MCP was particularly strong on villous cytotrophoblast cells and giant cells in first trimester tissues in comparison with other types of cells. In contrast, staining with anti-DAF was strong on proliferating cytotrophoblast in first trimester tissues, and on basal plate cytotrophoblast and decidual cells in term tissues. Placental villous mesenchymal cells but not trophoblast cells expressed a third regulatory protein, complement receptor 1. These observations support the postulate that complement regulatory proteins are critical to protection of the fetal allograft, and suggest specific requirements for trophoblast cells according to stage of differentiation and anatomic location.
Antigens, CD↗
Detection of class I MHC mRNA in subpopulations of first trimester cytotrophoblast cells by in situ hybridization.
Class I MHC mRNA has been identified in both villous and extravillous cytotrophoblast cells in first trimester placentas by in situ hybridization. In this report, we expand those observations to additional morphologically and anatomically distinct subpopulations of trophoblast cells in early placentas using the same experimental approach. In the transition zone of first trimester placental villi, where cytotrophoblast cells are proliferating to form new villi or to migrate into adjacent tissue, both cytotrophoblast cells beneath the uninterrupted syncytium and the proliferating cytotrophoblast cells contained class I mRNA whereas a layer of cytotrophoblast cells proximal to the villus core did not contain class I mRNA. In the placental bed, migrating cytotrophoblast cells contained high levels of class I mRNA as determined by the intensity of staining. In contrast, multinucleated giant trophoblast cells contained little specific message. Alterations in levels of class I mRNA seem therefore to be associated with trophoblast proliferation, migration and differentiation.
Female↗
Analysis of the expression and immunostimulatory capacity of class I major histocompatibility antigens on rat trophoblast cell lines.
In rat strains expressing the a and other major histocompatibility complex (MHC) haplotypes, subpopulations of placental trophoblast cells synthesize the nonclassical class I Pa antigen in preference to the classical RT1.Aa antigen. In this study, a rat trophoblast cell line, R8RP.3, which was derived from midgestation placentas of PVG.R8 (RT1.Aa) rats, was shown to express class I antigens similarly to those of trophoblast cells in situ. Both unstimulated and IFN-gamma-exposed metabolically labeled R8RP.3 cells synthesized more Pa than RT1.Aa antigen. The reverse was true for labeled spleen cells from PVG.R8 rats. The R8RP.3 cells failed to stimulate allogeneic lymphocyte proliferation even when high levels of both classical and nonclassical class I MHC antigens were expressed on their membranes after incubation with IFN-gamma. These experiments thus supply the first evidence that the inductive phase of the immune response is not promoted by trophoblast cell class I MHC antigens, which could explain the failure of mothers to mount immune responses to class I MHC positive trophoblast cells.
Animals↗
Tumor necrosis factor alpha mRNA and protein are present in human placental and uterine cells at early and late stages of gestation.
Tumor necrosis factor alpha (TNF-alpha), a polypeptide that regulates cellular growth and modulates the synthesis of various cell surface and secreted molecules, has been identified in the pregnant uterus. To determine which specific cells transcribed and translated this gene, extraembryonic fetal tissues (placenta and membranes) and uterine tissue from early and late stages of gestation were analyzed for TNF-alpha mRNA by in situ hybridization using biotinylated antisense and sense TNF-alpha probes, and for immunoreactive TNF-alpha using two monoclonal antibodies. Tumor necrosis factor-alpha transcripts and protein were identified in both extraembryonic and maternal cells. In first-trimester placental villi, TNF-alpha mRNA was present in syncytiotrophoblast but was low to absent in cytotrophoblast and villous stromal cells. Decidual and epithelial cells in maternal tissues contained TNF-alpha transcripts. In term placentas, both syncytiotrophoblast and villous stromal cells contained TNF-alpha mRNA, and transcripts were present in maternal cells in the decidua adjacent to the extraplacental membranes. In both first-trimester and term tissues, coincident expression of TNF-alpha mRNA and immunoreactive TNF-alpha was demonstrated. The results of this study show that TNF-alpha is synthesized by cells in both extraembryonic membranes and maternal tissues during human gestation and that transcription in specific types of cells is influenced by gestational age. These observations are consistent with a major role for TNF-alpha in the dynamic developmental events of human pregnancy.
Delivery, Obstetric↗
Differential responses of rat trophoblast cells and embryonic fibroblasts to cytokines that regulate proliferation and class I MHC antigen expression.
TNF-alpha and type I IFN (IFN-alpha/beta) are present in the uteroplacental unit during the course of normal gestation. IFN-gamma is likely to be present during infections. To identify potential effects on two types of blastocyst-derived cells, TNF-alpha, IFN-alpha/beta, and IFN-gamma were tested for the ability to modulate proliferation and the expression of class I MHC Ag by rat trophoblast cells and embryonic fibroblasts. The three cytokines had opposite influences on cellular proliferation by the two types of cells. Growth of the trophoblast cells was inhibited by TNF-alpha, IFN-alpha/beta, and IFN-gamma, whereas both TNF-alpha and IFN-alpha/beta enhanced fibroblast proliferation. The two endogenous cytokines had different effects on class I Ag expression by trophoblast cells and fibroblasts: TNF-alpha failed to induce trophoblast cell class I Ag and IFN-alpha/beta was a poor inducer whereas fibroblast Ag were induced by both cytokines. Moreover, combinations of TNF-alpha and IFN did not increase trophoblast cell class I Ag whereas the same combinations synergized to induce class I Ag expression by fibroblasts. In contrast, IFN-gamma was a highly efficient inducer on both types of cells. The results suggest that 1) cytokines in the uteroplacental unit may orchestrate some of the events associated with placental and embryonic development by exerting differential effects on two embryologically distinct types of cells and that 2) infections may disrupt normal events.
Animals↗
Identification of class I MHC mRNA in human first trimester trophoblast cells by in situ hybridization.
Special gestation-related regulatory mechanisms for the expression of class I Ag by trophoblast cells directly exposed to maternal blood and tissues may be required for semiallogeneic pregnancy to be successful. Analysis of class I MHC mRNA by in situ hybridization and class I MHC Ag by immunohistology has revealed two phenotypically distinct subpopulations of trophoblast cells in term placentas and extraplacental membranes. Trophoblast cells external to the placenta are mRNA +/Ag+. They contain class I mRNA and express class I Ag that differ serologically from HLA-A,B,C. In contrast, trophoblast cells forming the syncytial layer of placental villi are mRNA-/Ag-. By immunohistology, trophoblast cells in 1st trimester placental tissues are similar to those in term tissues. In our study, in situ hybridization was used to determine if patterns of trophoblast cell class I mRNA were the same or different. Trophoblast cells external to the placental villi in 1st trimester tissues contained class I mRNA as would be predicted from the results with term tissues. Unexpectedly, class I mRNA was found in villous trophoblast cells. Thus, these studies identified an mRNA+/Ag- trophoblast cell subpopulation. The results suggest that tissue-specific mechanisms may interfere with translation of class I mRNA in 1st trimester villous trophoblast cells and/or that the protein products of the mRNA are not identified by available mAb.
Female↗
Evasive strategies of trophoblast cells: selective expression of membrane antigens.
Contemporary experimental tools, particularly those of molecular biology, have allowed some insights on the selective display of membrane antigens by trophoblast cells. The unique observations offered by reproduction immunologists may have wider application than expected inasmuch as tumor cells may use some of the same mechanisms to avoid recognition and destruction by host immune cells and antibodies. Thus, further pursuit of the conditions that prevail in pregnancy may lead to a better understanding of the mechanisms used by "foreign" cells to coexist peaceably with host cells, bypassing immune mechanisms designed for their destruction.
Antigens, CD↗
Products of lipopolysaccharide-activated macrophages (tumor necrosis factor-alpha, transforming growth factor-beta) but not lipopolysaccharide modify DNA synthesis by rat trophoblast cells exhibiting the 80-kDa lipopolysaccharide-binding protein.
Pregnancy losses from gram negative bacterial infections could be caused by direct effects of LPS on placental cells, or indirectly via LPS activation of macrophages in the uteroplacental unit. To evaluate those alternatives, LPS, LPS-activated peritoneal cells, conditioned medium from LPS-activated peritoneal cells, and some purified and recombinant molecules known to be secreted by activated macrophages were tested for their abilities to modify DNA synthesis by rat trophoblast cells. Three trophoblast cell lines derived from midgestation placentas of outbred and inbred rats were used for the experiments. Although the 80-kDa LPS-binding protein was demonstrated on trophoblast cells, LPS alone had no effect on the ability of trophoblast cells to synthesize DNA. In cocultures, trophoblast cell DNA synthesis was slightly enhanced by low concentrations of both unstimulated and LPS-activated peritoneal cells. At higher concentrations, LPS-activated cells caused significant inhibition of DNA synthesis by trophoblast cells. Conditioned media from LPS-activated peritoneal cells were highly inhibitory to trophoblast cell DNA synthesis. When specific molecules likely to be components of those media were tested, IL-1 was found to have a modest but reproducible stimulatory effect and PGE2 did not change trophoblast cell incorporation of [3H]TdR. In contrast, trophoblast cell DNA synthesis was markedly inhibited in a dose-dependent manner by both TNF-alpha and TGF-beta 1. No differences in the sensitivity of trophoblast cells from outbred and inbred rats were observed. Given the limitations of the experimental model system, the results suggest that in cases of infection by gram-negative bacteria LPS may have an adverse effect on pregnancy by stimulating resident macrophages to generate and release molecules that are inhibitory to trophoblast cell DNA synthesis.
Animals↗
Cytokine networks in the uteroplacental unit: macrophages as pivotal regulatory cells.
A rich array of potent regulatory molecules has been identified in the uteroplacental unit. Most recently uncovered are the cytokines, families of polypeptides that establish intercellular communications, a paracrine effect, and often bind to synthetic cells in autocrine regulatory loops. Nearly all of the disparate maternal and fetal cell types in the uteroplacental unit are integrated into the cytokine network. The highly versatile macrophage, abundant in uteroplacental tissues, has emerged as a potentially pivotal cell type because of its unique ability to send and receive cytokine signals. Elevated levels of cytokines, possibly secreted when uteroplacental macrophages are activated by either bacterial endotoxins or receptor-bound cytokines, may compromise pregnancy. In particular, cytokines have been implicated in the induction of pre-term labor associated with infections. Intensive research is required to delineate the temporal patterns of cytokine synthesis that characterize pregnancy, to evaluate the events leading to normal and premature pregnancy termination and to establish protocols for therapeutic interventions in cases of infection.
Animals↗