Immune competence involving the natural killer cell lineage promotes placental growth

Detection of Math6-Expressing Cell Types in Murine Placenta

The transcription factor Math6, mouse atonal homolog 6, belongs to the family of highly conserved basic helix-loop-helix transcription factors. It plays an important role in embryonic development and shows a wide expression pattern in murine tissues. The placenta, as a life-sustaining transient organ for the fetus, also depends on the expression of Math6. The adverse effects of deleting Math6 in mice, leading to deficient placental development and pregnancy loss, have already been demonstrated by us. Until now, detailed investigations regarding the specific mechanisms underlying the improper placental development in these murine mutants have failed, as the Math6 expression could not be confined to a specific cell type due to the lack of a highly specific Math6 antibody. To circumvent this problem, we used transgenic mice, where Math6 is marked with a Flag sequence that functions as a specific epitope. Tissues from these transgenic mice were used to establish immunohistochemical staining and fluorescence-activated cell sorting (FACS). The establishment of these methods yielded initial findings pertaining to the identification of Math6-expressing cell types and their localization. Our results reveal that Math6 shows a wide expression pattern in both maternal and fetal components of the murine placenta. It shows expression in various cell types, but predominantly in trophoblast giant cells, endothelial cells and macrophages. The largest subpopulation that we detected in the group of Math6-positive cells were identified as DBA+ uterine natural killer cells. These findings reveal information and a chance for further investigation on the involvement of Math6 in placental development and the molecular pathomechanisms of spontaneous abortion.

Immunity at maternal-fetal interface: KIR/HLA (Allo)recognition

Both KIR and HLA are the most variable gene families in the human genome. The recognition of the semi-allogeneic embryo-derived trophoblasts by maternal decidual NK (dNK) cells is essential for the establishment of the functional placenta. This recognition is based on the KIR-HLA interactions and trophoblast expresses a specific HLA profile that constitutes classical polymorphic HLA-C and non-classical oligomorphic HLA-E, HLA-F, and HLA-G molecules. This review highlights some features of the KIR/HLA-C (allo)recognition by decidual NK (dNK) cells as a main immune cell population specifically enriched at maternal-fetal interface during human early pregnancy. How KIR/HLA-C axis operates in pregnancy disorders and in the context of transplacental infections is discussed as well. We summarized old and new data on dNK-cell functional plasticity, their selective expression of KIR and fetal maternal/paternal HLA-C haplotypes present. Results showed that KIR-HLA-C combinations and the corresponding axis operate differently in each pregnancy, determined by the variability of both maternal KIR haplotypes and fetus' maternal/paternal HLA-C allotype combinations. Moreover, the maturation of NK cells strongly depends on if or not HLA allotypes for certain KIR are present. We suggest that the unique KIR/HLA combinations reached in each pregnancy (normal and pathological) should be studied according to well-defined guidelines and unified methodologies to have comparable results ease to interpret and use in clinics.

Extracellular vesicles generated by placental tissues ex vivo: A transport system for immune mediators and growth factors

PROBLEM

To study the mechanisms of placenta function and the role of extracellular vesicles (EVs) in pregnancy, it is necessary to develop an ex vivo system that retains placental cytoarchitecture and the primary metabolic aspects, in particular the release of EVs and soluble factors. Here, we developed such a system and investigated the pattern of secretion of cytokines, growth factors, and extracellular vesicles by placental villous and amnion tissues ex vivo.

METHODS OF STUDY

Placental villous and amnion explants were cultured for 2 weeks at the air/liquid interface and their morphology and the released cytokines and EVs were analyzed. Cytokines were analyzed with multiplexed bead assays, and individual EVs were analyzed with recently developed techniques that involved EV capture with magnetic nanoparticles coupled to anti-EV antibodies and flow cytometry.

RESULTS

Ex vivo tissues (i) remained viable and preserved their cytoarchitecture; (ii) maintained secretion of cytokines and growth factors; (iii) released EVs of syncytiotrophoblast and amnion epithelial cell origins that contain cytokines and growth factors.

CONCLUSION

A system of ex vivo placental villous and amnion tissues can be used as an adequate model to study placenta metabolic activity in normal and complicated pregnancies, in particular to characterize EVs by their surface markers and by encapsulated proteins. Establishment and benchmarking the placenta ex vivo system may provide new insight in the functional status of this organ in various placental disorders, particularly regarding the release of EVs and cytokines. Such EVs may have a prognostic value for pregnancy complications.

Identification of the primary outcomes that result from deficient spiral arterial modification in pregnant mice

Pre-eclampsia, an acute complication of human pregnancy, is associated within complete physiological modification of decidual spiral arteries. This is thought to promote oxidative stress from perfusion/reperfusion of the placenta and to restrict placental and fetal growth. Alymphoid (genotype Rag2(-/-)/Il2rg(-/-)) mice, sufficient in dendritic and myeloid cell functions, lack spiral arterial modification with individual spiral arteries having ~1.7x the vascular resistance and 0.66x the blood velocity of +/+ mice. Their placentae are measurably hypoxic yet neither placental growth nor fetal survival is impaired and gestational hypertension is not seen. Thus, lymphocytes rather than vascular adaptations appear to be the pivotal contributors to the clinical complications of pre-eclampsia.

The differential expression of microRNAs between implantation sites and interimplantation sites in early pregnancy in mice and their potential functions

Embryo implantation is a complex process that involves synchronized crosstalk between a receptive endometrium and a functional blastocyst. It can take place only during the window of implantation, a period when a series of changes in gene expression occur in the endometrium to accept the embryo. As modulators of gene expression, microRNAs (miRNAs) have been identified as regulators of embryo implantation. To better understand how miRNAs regulate implantation and the related molecular mechanisms, we compared the expression profiles of miRNAs and messenger RNAs between implantation sites (IMs) and inter-IMs in the endometrium of pregnant mice on day 5 by microarrays. The results showed that compared with inter-IMs, 30 miRNAs were upregulated and 42 miRNAs (>2-fold) were downregulated at the IMs. By combining the results of the microarray experiments, we found that 20 upregulated pathways and 14 downregulated pathways might be subject to miRNA regulation at IMs. We also found that some miRNAs and their targets may play a key role in implantation.

Progesterone-mediated immunomodulation in pregnancy: its relevance to leukocyte immunotherapy of recurrent miscarriage

Progesterone is crucial for the establishment and maintenance of pregnancy. Progesterone-regulated genes in the pregnant uterus control the development of endometrial receptivity as well as recruitment and differentiation of decidual NK cells, which in turn act on angiogenesis and trophoblast invasion. The link between progesterone and the immune system is established by lymphocyte progesterone receptors expressed in peripheral blood gammadelta T cells of pregnant women and in peripheral NK cells. Regulation of lymphocyte progesterone receptors is activation related, thus efficient recognition of fetal antigens is a requirement for the initiation of progesterone-dependent immunoregulatory mechanisms. Several immunological effects of progesterone are mediated by progesterone-induced blocking factor--the product of a progesterone-induced gene in lymphocytes. One part of unexplained recurrent miscarriages might have an immunological etiology. Immunization of the mothers with paternal or third-party leukocytes aims to correct the misregulated antifetal immune response. There are, however, serious concerns about this treatment, including the lack of information about the mode of action and possible adverse effects of the treatment, the failure to detect a significant effect of immunotherapy and the lack of a reliable generally accepted marker for patient selection. These concerns will be discussed in this review.

Uterine natural killer cells are immunogenic in syngeneic male mice

Uterine natural killer (uNK) cells expand rapidly during endometrial decidualization and account for 70% of leukocytes in early gestational uteri of humans and rodents. These cells make unique contributions to pregnancy, contributing to the success of embryo implantation and maintenance of decidual tissue that supports placental and fetal development. We postulated that uNK cells express molecules that are not shared by circulating NK (cNK) cells or other leukocytes and, therefore, would be immunogenic for male mice. We isolated viable uNK cells from gestation day 9 pregnant mice and inoculated them into syngeneic males. This induced antibodies reactive with mouse uNK cells but not with cNK cells or other lymphocytes. The antibodies reacted identically with uNK cells in tissue sections from five different mice strains from gestational day 7-12 and in pregnant rat uterus, suggesting that the recognized antigen should be a specific marker of uNK cell. Spleen cells from inoculated males were used subsequently to produce a monoclonal antibody reactive to a uNK cell surface antigen. These experiments confirm that uNK cells are a pregnancy-specific subset of NK cells expressing distinct surface antigen from those found in other tissues.

The fetal allograft revisited: does the study of an ancient invertebrate species shed light on the role of natural killer cells at the maternal-fetal interface?

Human pregnancy poses a fundamental immunological problem because the placenta and fetus are genetically different from the host mother. Classical transplantation theory has not provided a plausible solution to this problem. Study of naturally occurring allogeneic chimeras in the colonial marine invertebrate, Botryllus schlosseri, has yielded fresh insight into the primitive development of allorecognition, especially regarding the role of natural killer (NK) cells. Uterine NK cells have a unique phenotype that appears to parallel aspects of the NK-like cells in the allorecognition system of B. schlosseri. Most notably, both cell types recognize and reject "missing self" and both are involved in the generation of a common vascular system between two individuals. Chimeric combination in B. schlosseri results in vascular fusion between two individual colonies; uterine NK cells appear essential to the establishment of adequate maternal-fetal circulation. Since human uterine NK cells appear to de-emphasize primary immunological function, it is proposed that they may share the same evolutionary roots as the B. schlosseri allorecognition system rather than a primary origin in immunity.

Basic aspects of implantation

Implantation, a critical step for establishing pregnancy, requires molecular and cellular events resulting in healthy uterine growth and differentiation, blastocyst adhesion, invasion and placental formation. Successful implantation requires a receptive endometrium, a normal and functional embryo at the blastocyst stage and a synchronized dialogue between maternal and embryonic tissues. In addition to the main role of sex steroids, the complexity of embryo implantation and placentation is exemplified by the number of cytokines and growth factors with demonstrated roles in these processes. Disturbances of the normal expression and action of these cytokines result in absolute or partial failure of implantation and abnormal placental formation in mice and humans. Members of the gp130 cytokine family, interleukin (IL)-11 and leukaemia inhibitory factor, the transforming growth factor-beta superfamily, colony-stimulating factors, and the IL-1 and IL-15 systems are all crucial for successful implantation. In addition, chemokines are important both in recruiting specific cohorts of leukocytes to the implantation site, and in trophoblast trafficking and differentiation. This review provides discussion on embryonic and uterine factors that are involved in the process of implantation in autocrine, paracrine and/or juxtacrine manners at hormonal, cellular, and molecular levels.

Immunology of normal pregnancy

Since Medawar's initial contemplations in 1953 on the mechanisms of immune evasion allowing for the survival of the allogeneic conceptus in an immunologically competent mother, physicians and immunologists alike have struggled to understand the immunological paradox of pregnancy. Ultimately, our attempts to define the immunology of normal pregnancy have broadened our appreciation of the myriad mechanisms at play that enable the promotion of implantation and maintenance of pregnancy. In this review, we summarise what is known regarding the immunology of normal pregnancy, with special emphasis on the relation to common disorders of pregnancy.

Human decidual natural killer cells as a source and target of macrophage migration inhibitory factor

The human uterine mucosa of early pregnancy is largely populated by CD56(bright) natural killer (NK) cells (uterine (u) NK cells). The specific functions of these cells are still unknown, but their interaction and response to foetal trophoblasts are thought to be important for the establishment of a successful pregnancy. The study reported herein shows that uNK cells respond to, and produce, macrophage migration inhibitory factor (MIF), a cytokine highly expressed in the human placenta and in the cyclic and pregnant endometrium. Recombinant human MIF reduced in a dose-dependent manner the cytolytic activity of purified uNK cells against K562 cells. RT-PCR, Western blot analysis and ELISA demonstrated the synthesis and secretion of the cytokine by uNK cells. Double immunofluorescence staining showed the presence of MIF in uterine CD56 + cells. Finally, neutralization of the endogenous cytokine by a polyclonal antibody resulted in a sharp increase in the cytolytic activity of uNK cells. These findings indicate the existence of a previously unrevealed paracrine and autocrine action of MIF on uNK cells and support its contribution to the immune privilege at the maternal-foetal interface.

Interactions between natural killer cells, cortisol and prolactin in malaria during pregnancy

Natural killer cells derived from pluripotent hematopoietic stem cells are important cells of the immune system that have two main functions: a cytolytic activity and a cytokine-producing capacity. These functions are tightly regulated by numerous activating and inhibitory receptors, including newly discovered receptors that selectively trigger the cytolytic activity in a major histocompatibility complex independent manner. Based on their defining function of spontaneous cytotoxicity without prior immunization, natural killer (NK) cells have been thought to play a critical role in immune surveillance and cancer therapy. New insights into NK cell biology have suggested their major roles in the control of infections, particularly in Plasmodium falciparum infection and in fetal implantation. P. falciparum is the main protozoan parasite responsible for malaria causing 200-300 million clinical cases and killing over 3 million people each year. This review provides an update on NK cell function, ontogeny and biology in order to better understand the role of NK cells in pregnancy in regions where malaria is endemic. Understanding mechanisms of NK cell functions may lead to novel therapeutic strategies for the treatment of human disease, in general, and particularly in the fight against malaria.

Ultrastructural Study of Uterine Natural Killer Cells Found in Pregnant, Interleukin-2 Receptor .BETA.-chain Overexpressed Transgenic Mice

We previously reported that all fetuses died or were resorbed on day 12 of pregnancy (Day 1= the day of plug) in interleukin-2 (IL-2) receptor beta-chain overexpressed transgenic (Tg2Rbeta) mice. In this study, to clarify the role of uterine natural killer (uNK) cells in pregnancy, the ultrastructure of Tg2Rbeta mouse uNK cells was analyzed using a transmission electron microscope. uNK cells and their granules on day 10 of pregnancy were larger in Tg2Rbeta mice than control mice, indicating that differentiation of uNK cells in Tg2Rbeta mice progressed rapidly. Additionally, the granules of uNK cells in Tg2Rbeta mice on day 10 of pregnancy had an irregular morphology. The multivesicular regions were present in the cap structure of these granules, suggesting that the uNK cells of the Tg2Rbeta mice had cytotoxic activity.

Interferon-tau stimulates secretion of macrophage migration inhibitory factor from bovine endometrial epithelial cells

During early pregnancy in ruminants, the embryo not only prevents prostaglandin F2alpha release, but it also modifies protein synthesis in the endometrium. This is accomplished by the secretion of interferon-tau (IFN-tau) from the embryo. The objective of this study was to identify and characterize specific proteins secreted from endometrial epithelial cells in response to IFN-tau that could be important for endometrial function and/or embryo development. The epithelial cells were prepared and cultured to confluence and then incubated with or without 100 ng/ml IFN-tau. At the end of the incubation, the proteins in the medium were analyzed by two-dimensional PAGE. The result showed that two major protein spots were induced by IFN-tau. One has a molecular mass of approximately 12 kDa and an isoelectric point (pI) of 6.7; the other has a molecular mass of 76 kDa and pI of 4.8. Protein sequence analysis showed that the 12-kDa protein contained a partial amino acid sequence that corresponded to macrophage migration inhibitory factor (MIF). To determine whether MIF is expressed in endometrial cells, isolated stromal or epithelial cells were incubated with or without 100 ng/ml IFN-tau for 0, 3, 6, 12, 24, and 48 h. After incubation, the MIF protein in cells was examined by Western blotting analysis, and the steady-state mRNA for MIF was examined by Northern analysis. Results showed that MIF protein and mRNA were present in the epithelial cells but not the stromal cells. The presence of MIF in the luminal epithelium of endometrial tissue was confirmed by immunohistochemistry. However, there was no effect of IFN-tau on MIF expression in the epithelial cells. The concentration of MIF in the medium was quantified by Western blotting analysis to determine if IFN-tau altered MIF protein secretion from the epithelial cells. The results showed that IFN-tau significantly stimulated the secretion of MIF protein from the cells. These data show that MIF is expressed in the epithelial, but not the stromal, cells of the endometrium and that MIF secretion from the epithelial cells is stimulated by IFN-tau. It is therefore likely that MIF plays a role in early embryo development, and further characterization of MIF expression and its regulation in the endometrium will add significantly to our understanding of early embryo-uterine interactions.

Prolactin-like protein-A is a functional modulator of natural killer cells at the maternal-fetal interface

Natural killer (NK) cells are the predominant lymphocytes present in healthy rodent and human implantation sites. In the rat, the expansion, differentiation and subsequent migration of NK cells away from the developing chorioallantoic placenta coincide with the expression of a novel pregnancy- and trophoblast cell-specific cytokine, prolactin (PRL)-like protein A (PLP-A). PLP-A specifically binds to uterine NK cells but does not appear to utilize receptor systems for PRL. In the present report, we show that PLP-A interactions with NK cells are not mediated by receptors utilized by known modulators of NK cell function, including interleukin-2, interleukin-7, interleukin-12, and interleukin-15 (IL-15). Uterine NK cells respond to PLP-A or IL-15 with an increase in intracellular calcium mobilization. In contrast, PLP-A, unlike IL-15, effectively suppresses the ability of NK cells to produce interferon-gamma (IFNgamma), a key mediator of NK cell function. Placental PLP-A expression is reciprocal to mesometrial decidua expression of IFNgamma. Increased expression of PLP-A by the placenta coincides with the decline of IFNgamma content in the mesometrial decidua adjacent to the placenta. In summary, trophoblast cell-derived PLP-A contributes to the regulation of NK cells at the maternal-fetal interface to ensure appropriate embryonic growth and development.

Demonstration of the presence of IL-16, IL-17 and IL-18 at the murine fetomaternal interface during murine pregnancy

PROBLEM

To determine if interleukin-16 (IL-16), IL-17, and IL-18 are present at the murine fetomaternal interface during pregnancy as a first step towards investigating their roles in fetomaternal relationship.

METHODS

Expression of IL-16, IL-17, and IL-18, was assessed by immunohistochemistry (IHC) in the BALB/c x BALB/k (H2d x H2k), and the CBA/J x BALB/c non-abortion prone, and CBA/J x DBA/2 abortion prone matings. Enzyme-linked immunosorbent assay (ELISA) were performed for the two latter cytokines to compare local production in the abortion prone CBA/J x DBA/2 versus the non-abortion prone CBA/J x BALB/c matings.

RESULTS

Expression of IL-17 was borderline. The anti-IL-16 staining specifically localized in the uterine stroma and glandular epithelium and was rather low in the placenta. IL-18 staining started in the peri-implantation uterus in the basal proliferative stroma, and was also traced, although weaker, in the glandular epithelium. In the immediate post-implantation period, a weak stromal staining persisted but there was a strong labeling of the ectoplacental cone. Interestingly, when the ectoplacental cone differentiates into placenta having a major histocompatibility complex (MHC) class I + spongiotrophoblast and a (MHC class I-) labyrinth, a very strong transient labeling of uterine natural killer (u-NK) cells was found. Later in gestation, IL-18 was also produced by giant cell and spongiotrophoblast. Finally, we compared by ELISA the production of IL-17/-18 in CBA/J x DBA/2 and CBA/J x BALB/c matings. We detected significantly more IL-18 in the non-abortion prone combination decidua or placenta.

CONCLUSION

The three cytokines IL-16, IL-17, and IL-18 were detected at the fetomaternal interface with a tissue specific, stage-dependent distribution. The predominance of IL-18 secretion in the non-resorption prone matings lead us to question the general validity of the classical T-helper (Th)1/2 paradigm.

Decidual natural killer cells: key regulators of placental development (a review)

Establishment of pregnancy initiates a dynamic and predictable series of changes in the uterus. In rodents, the trophectoderm of the blastocyst develops through the stage of an ectoplacental cone to become the placenta. The inner cell mass becomes the fetus and its associated extra-embryonic ectoderm and mesoderm. Maternal changes support development of the conceptus. These begin in the uterine stroma, which undergoes a process known as decidualization, and progress to include dilation and elongation of the uteroplacental arteries and activation and proliferation of specialized large granulated lymphocytes in the decidua basalis. This review focuses on these pregnancy-associated lymphocytes, known as uterine Natural Killer (uNK) cells and on their interactions with the other tissues that form the mesometrial aspect of the mouse maternal-fetal interface. Analogous lymphocytes are present in the decidualized human uterus. Understanding of uNK cell biology has advanced significantly through histological studies of implantation sites in immune deficient mice. Here, we summarize the key studies in lymphocyte-, cytokine- and cytokine receptor-deficient mice and in four enhanced models of gestation in these mice that incorporate transplantation or therapy with biologically active molecules.

The biology of natural killer cells in cancer, infection, and pregnancy

OBJECTIVE

NK cells are important cells of the immune system. They are ultimately derived from pluripotent hematopoietic stem cells. NK cell cytotoxicity and other functions are tightly regulated by numerous activating and inhibitory receptors including newly discovered receptors that selectively recognize major histocompatibility complex class I alleles. Based on their defining function of spontaneous cytotoxicity without prior immunization, NK cells have been thought to play a critical role in immune surveillance and cancer therapy. However, new insights into NK cell biology have suggested major roles for NK cells in infection control and uterine function. The purpose of this review is to provide an update on NK cell function, ontogeny, and biology in order to better understand the role of NK cells in health and disease.

DATA SOURCES

In the Medline database, the major subject heading "Natural Killer Cells" was introduced in 1983, identifying 16,848 citations as of December 31, 2000. Since 1986, there have been approximately 1000 citations per year under this subject heading. In this database, 68% of manuscripts are limited to human NK cells; 40% of citations cross with the major sub-heading of cytotoxicity, 40% with cytokines, 36% with neoplasm, 5% with antibody-dependent cellular cytotoxicity, 2.8% with pregnancy, and 1.3% with infection. Of references from the year 2000-2001, 46 were selected to combine with contributions from earlier literature.

CONCLUSIONS

NK cells should no longer be thought of as direct cytotoxic killers alone as they clearly serve a critical role in cytokine production which may be important to control cancer, infection, and fetal implantation. Understanding mechanisms of NK cell functions may lead to novel therapeutic strategies for the treatment of human disease.

Macrophage migration inhibitory factor in the human endometrium: expression and localization during the menstrual cycle and early pregnancy

Macrophage migration inhibitory factor (MIF) was discovered as an activated T-lymphocyte-derived protein that inhibits the random migration of macrophages in vitro. Subsequently, knowledge of the physiological actions of MIF was extended to include its role as a proinflammatory cytokine that affects several functions of macrophages and lymphocytes. Previous reports have suggested an involvement of MIF in reproduction. However, no data are currently available on the presence of this cytokine in the human endometrium. In this study, the expression and tissue localization of MIF was evaluated in specimens of cycling endometrium, first trimester placenta bed biopsy, and isolated endometrial glands by Western blot analysis, immunohistochemistry, ELISA, and reverse transcription-polymerase chain reaction. The results demonstrated that MIF is expressed in human endometrium across the menstrual cycle and in early pregnancy. Immunohistochemical localization identified the protein in glandular epithelium, in stromal and predecidualized stromal cells of cycling endometrium, as well as in the decidua of first-trimester placenta. The proinflammatory features and specific actions of MIF on lymphoid cells suggest its potential involvement in several aspects of endometrial physiology.

Angiogenic growth factor messenger ribonucleic acids in uterine natural killer cells

Angiogenesis is essential for endometrial growth and repair, and disruption of this process may lead to common disorders of women, including menorrhagia and endometriosis. In pregnancy, failure of the endometrial spiral arterioles to undergo remodeling leads to preeclampsia. Here we report that in addition to vascular endothelial growth factor A (VEGF-A), human endometrium expresses messenger ribonucleic acids (mRNAs) encoding VEGF-C, placenta growth factor (PlGF), the angiopoietins, angiopoietin 1 (Ang1) and Ang2, and the receptors VEGFR-3 (Flt-4), Tie 1, and Tie 2. Levels of VEGF-C, PlGF, and Tie 2 changed during the menstrual cycle. Intense hybridization for VEGF-C and PlGF mRNAs was found in uterine nature killer cells in secretory phase endometrium and for Ang2 mRNA in the same cells in the late secretory phase. Interleukin-2 (IL-2) and IL-15 up-regulated VEGF-C, but not PlGF or Ang2, mRNA levels in isolated NK cells. Conditioned medium from decidual NK cells did not induce human umbilical vein endothelial cell apoptosis. These results indicate that human endometrium expresses a wide range of angiogenic growth factors and that uterine nature killer cells may play an important role in the abnormal endometrial angiogenesis that underlies a range of disorders affecting women.

Local versus systemic control of numbers of endometrial T cells during pregnancy in sheep

Pregnancy in sheep is associated with changes in numbers of specific T-lymphocyte populations in the uterine endometrium. These changes probably contribute to evasion by the conceptus of maternal immunological rejection and indicate a possible role for T cells in placental growth, parturition and post-parturient uterine defence against infection. The purpose of the present experiment was to evaluate the relative importance of systemic signals (i.e. those present throughout the uterus or from the circulation, including conceptus hormones secreted into the maternal blood) versus locally acting conceptus signals for regulating changes in numbers of endometrial lymphocytes during pregnancy. The approach taken was to surgically confine pregnancy to one uterine horn and compare differences in lymphocyte numbers between the two uterine horns as well as between both horns of pregnant ewes with those of ovariectomized ewes. As compared with ovariectomized ewes, there was a decline in numbers of CD45R+ lymphocytes within glandular epithelium and an increase in gammadelta T-cell number within the luminal epithelium. These changes occurred in both the pregnant and non-pregnant uterine horns of unilaterally pregnant ewes. Moreover, there were no significant differences in lymphocyte numbers between the two uterine horns of unilaterally pregnant ewes. Expression of CD25 was absent in tissues from both uterine horns. In conclusion, changes in numbers of endometrial lymphocytes during pregnancy, rather than due to locally acting signals of conceptus origin, are the result of hormonal signals of maternal or conceptus origin that either act directly on endometrial lymphocytes or stimulate the uterine endometrium to induce synthesis of regulatory molecules that affect lymphocyte dynamics.

A study of reproductive performance in pregnant, IL-2 receptor beta-chain overexpressed transgenic mice

Relationships between female reproductive performance and uterine natural killer (uNK) cells were investigated in pregnant IL-2 receptor beta-chain overexpressed transgenic (Tg2Rbeta) mice. At 8 days of pregnancy, all fetuses were alive, suggesting that implantation normally occurred in these mice. However, 47% of fetuses were dead at 10 days of pregnancy and at 12 days all fetuses were resorbing, indicating that fetal loss progressed with the advance of pregnancy. The placenta of Tg2Rbeta mice gradually decreased in weight with the advance of pregnancy. At 10 days the placental labyrinth, decidua basalis, and metrial gland in Tg2Rbeta mice were poorly developed, and more uNK cells were found in Tg2Rbeta mice than in the control mice. We propose that Tg2RPbeta mice are the first and interesting model that uNK cells can cause abortion, to clarify the involvement of uNK cell function in female reproductive performance.

Progesterone enhances interleukin-15 production in human endometrial stromal cells in vitro

Interleukin-15 (IL-15) is a novel cytokine that stimulates lymphocyte proliferation and migration via a trimeric receptor sharing the ss and gamma signal-transducing chains with the IL-2 receptor. It is suggested that IL-15 is involved in regulating the proliferation and differentiation of uterine natural killer cells. In the human endometrium, we have recently reported that IL-15 messenger ribonucleic acid (mRNA) levels significantly increased during the secretory phase compared with those during the proliferative phase. In this study we investigated whether the female sex steroids progesterone (P) and estradiol (E(2)) regulate IL-15 messenger RNA (mRNA) and the secretion in human endometrial stromal cells (ESC) in vitro. Northern blot analyses revealed a significant increase in IL-15 mRNA levels in ESC treated with P alone or E(2) plus P compared with vehicle. Furthermore, P is a potent inducer of IL-15 mRNA expression in ESC in a dose-dependent manner. On the other hand, E(2) alone did not increase IL-15 mRNA expression. By enzyme-linked immunosorbent assay, IL-15 protein secretion was stimulated by P and further enhanced by combined treatment with E(2) and P, whereas E(2) alone was ineffective. It is suggested that IL-15 is deeply involved in the hormonal control of the human endometrium by P and E(2).

Ultrastructural studies of implantation sites from mice deficient in uterine natural killer cells

Implantation sites from three strains of immunodeficient mice [tgepsilon26, IL-2Rbeta nullxp56(lck)null and IL-2Rgamma null, now known as common cytokine chain gamma (gamma(c)) null], which lack uterine natural killer (uNK) cells, are histologically abnormal. The related anomalies (found from day 10 of gestation) include the absence of aggregation of lymphocytes in the mesometrial triangle, acellularity of the mesometrial decidua, decidual arteries with relatively thick walls and reduced lumen diameters, unusual prominence of the endothelium in the major decidual vessels, and an overall reduction in placental size. In this study we have characterized implantation sites in a new mouse strain (gammac(-)/RAG2(-)) that is deficient in all lymphoid lineages. We have compared implantation sites in tgepsilon26 to gammac(-)/RAG2(-)at the ultrastructural level in order to determine the earliest-time point at which implantation sites differed from those in immunocompetent mice, and the cell types affected. Implantation sites from both the uNK cell-deficient mice resemble those from random-bred, immunocompetent mice on days 6 and 7 of gestation. On day 8 of gestation, decidual cells on the mesometrial sides of implantation sites in both tgepsilon26 and gammac(-)/RAG2(-)revealed pleotrophic morphology and degeneration. In some vessels, endothelial cells were distorted or displaced from their supporting cells. Progressive changes, suggestive of loss of function of both the mesometrial decidua and endothelial cells, were seen to day 14 of gestation, the latest time-point analysed. In contrast to tgepsilon26 mice, homozygously-mated gammac(-)/RAG2(-)had normal litter sizes, with birthweights and weaning weights similar to congenic C57Bl/6J controls, and no significant perinatal loss. In both strains, the newly-documented endothelial cell lesions predict detrimental alterations to vasomotor function of the uterine vasculature. These studies add strength to the hypothesis that uNK cells may have specialized physiological, rather than classically immune, functions in the pregnant mammalian uterus.

E-selectin expression and function in a unique placental trophoblast population at the fetal-maternal interface: regulation by a trophoblast-restricted transcriptional mechanism conserved between humans and mice

Trophoblast are the earliest differentiated cells to emerge during mammalian ontogeny. Proper differentiation and maturation of trophoblast contributes to the fetal-maternal vascular interface of the mature placenta and is required for all subsequent stages of embryogenesis. Although lineage commitment and early differentiation of trophoblast have been investigated experimentally, molecular markers and regulatory mechanisms operating later in trophoblast development remain uncertain. We now report that E-selectin is expressed in a unique pattern in secondary trophoblast giant cells, trophoblast lining the central artery, and a subpopulation of labyrinthine trophoblast all located at the fetal-maternal interface of the murine placenta. These cells line vascular channels but express a unique profile of gene products not displayed by vascular endothelium. Placentae lacking E-selectin show increased trophoblast glycogen cells and fewer labyrinthine neutrophils compared with normal placentae, suggesting that recognition of E-selectin on trophoblast by counter-receptors on other cells contributes to placental development. Novel, distant first exons direct E-selectin expression in both murine and human placentae, suggesting that evolutionarily conserved and lineage-restricted transcriptional mechanisms regulate expression in homologous trophoblast populations in both species. These results define, at molecular and anatomic levels, a unique population of trophoblast located at the physiologically critical fetal-maternal vascular interface in mice. We also present initial functional characterization of E-selectin in placenta. These results support the general hypothesis that endothelial-leukocyte adhesion molecules performing specialized functions in adults may also function in development of human and murine hemochorial placentae.

Transplantation into genetically alymphoid mice as an approach to dissect the roles of uterine natural killer cells during pregnancy--a review

Mice genetically deficient in the natural killer (NK) cell lineage lack uterine (uNK cells) and demonstrate morphometrically-quantifiable histopathology within their implantation sites. Two particular mouse strains, tg(epsilon),26 and RAG-2 null x gamma(c) null, have been used successfully as transplant recipients to address questions relating to the biology of uNK cells. uNK cells did not differentiate within decidualized uterine graft segments from normal mice, which were anastomosed orthotopically into immunodeficient hosts. uNK cells did appear in similar grafts placed into immunocompetent hosts, indicating that uNK cells or their progenitors must home to the uterus. This was confirmed by splenocyte transplantation into pregnant uNK cell deficient recipients. Only splenocytes from pregnant donors, not those from non-pregnant donors, homed to the uterus. Homing in this in vivo assay was independent of the CC-chemokine receptors, CCR-2 and CCR-5. Longer-term bone marrow cell reconstitution of neonatal or virgin adult uNK cell-deficient mice has identified a functional role for uNK cells in modification of the decidual arterioles which is mediated by IFN-gamma. By utilizing mutant and gene-ablated mice as donors for tissue or haematopoietic cell transplants to uNK cell deficient mice, it should be possible to fully characterize the in vivo regulation and functions of these pregnancy-specific uterine lymphocytes.