Migration of leucocytes into the uterus after acute removal of ovarian progesterone during early pregnancy in the sheep

The Ruminant Placental Trophoblast Binucleate cell - an evolutionary breakthrough

Viviparity and the development of a placenta are two of the major reasons for the success of the mammals in colonizing all habitats, both terrestrial and aquatic. The placenta is an apposition of fetal to maternal tissue which serves two main, but competing functions: to maximize oxygen transfer and the acquisition of nutrients from the mother, but to minimize immunological rejection by the maternal immune system. This has resulted in the evolution of four main types differing in the degree of loss of the maternal uterine epithelial (UE) barrier: epitheliochorial, synepitheliochorial, endotheliochorial, and hemochorial, all providing a successful safe balance between the needs of mother and fetus. Epitheliochorial is the least invasive, a simple apposition and microvillar interdigitation of the apices of uterine epithelium and trophoblast. It is suggested to have evolved as a response to the increase in the size of the animal to provide a sufficiently long gestation to produce a single altricial (run/swim-soon-as-born) neonate as in the Cetartiodactyla. The mother needs to have good control of the fetal demands so the UE barrier is maintained. However, in the synepitheliochorial placenta, characteristic of all ruminants, the fetus has evolved a means of increasing, or at least maintaining, demand without the need for invasion. This has been achieved by the development of the trophoblast binucleate cell which, uniquely, can fuse with a UE cell to form fetomaternal hybrid tissue. This can maintain some maternal barrier function but also deliver fetally synthesized immunomodulatory and metabolic messages to the maternal circulation. This review provides the evidence for this remarkable evolutionary step and also considers an alternative explanation for the formation of the structure of the ruminant placenta.

Embryo implantation evolved from an ancestral inflammatory attachment reaction

The molecular changes that support implantation in eutherian mammals are necessary to establish pregnancy. In marsupials, pregnancy is relatively short, and although a placenta does form, it is present for only a few days before parturition. However, morphological changes in the uterus of marsupials at term mimic those that occur during implantation in humans and mice. We investigated the molecular similarity between term pregnancy in the marsupials and implantation in eutherian mammals using the gray short-tailed opossum (Monodelphis domestica) as a model. Transcriptomic analysis shows that term pregnancy in the opossum is characterized by an inflammatory response consistent with implantation in humans and mice. This immune response is temporally correlated with the loss of the eggshell, and we used immunohistochemistry to report that this reaction occurs at the materno-fetal interface. We demonstrate that key markers of implantation, including Heparin binding EGF-like growth factor and Mucin 1, exhibit expression and localization profiles consistent with the pattern observed during implantation in eutherian mammals. Finally, we show that there are transcriptome-wide similarities between the opossum attachment reaction and implantation in rabbits and humans. Our data suggest that the implantation reaction that occurs in eutherians is derived from an attachment reaction in the ancestral therian mammal which, in the opossum, leads directly to parturition. Finally, we argue that the ability to shift from an inflammatory attachment reaction to a noninflammatory period of pregnancy was a key innovation in eutherian mammals that allowed an extended period of intimate placentation.

Dynamics of CD3⁺ T-cell distribution throughout the estrous cycle and gestation in the bovine endometrium

T cells are the dominant lymphocytes in the endometrium and are considered to play a crucial role in implantation and in the maintenance of gestation through cytokine production and immune regulation. The mechanisms underlying immunoregulation at the feto-maternal interface are still obscure for this complex system. Understanding the role of T cells is a key factor in understanding the endometrial immune system. In this study, the distribution of endometrial CD3⁺ T cells in bovines was examined by immunohistochemical analysis. The estrous cycle and gestation was divided into 4 stages, and the number of CD3⁺-positive T cells was counted in each stage. CD3⁺ cells were found in the endometrium in significant numbers throughout the estrous cycle and were mostly located in the subepithelial area. The number of CD3⁺ cells significantly increased in the early and mid-luteal phases but decreased after implantation with the progression of gestation. No T cells were found in the placentome or specifically in the tissues near the fetus, including the trophoblastic area. In addition, very few T cells were found in stromal regions close to the myometrium of the endometrium. These findings suggest that downregulation of bovine endometrial CD3⁺ T-cell functions is closely related to the successful maintenance of gestation in a spatiotemporal manner.

Neuroendocrine factors alter host defense by modulating immune function

An increasing body of evidence demonstrates that there is bidirectional communication between the neuroendocrine and immune systems. Interaction between these systems results in a variety of outcomes, including the well documented "sickness behavior" elicited by cytokines of the immune system that can enter the brain and activate second messengers that modify neuronal activity. Crosstalk between the neuroendocrine and immune systems can also result in production of factors by the nervous and endocrine systems that alter immune cell function and subsequent modulation of immune responses against infectious agents and other pathogens. Continued exposure to molecules produced by the neuroendocrine system has also been known to increase susceptibility and/or severity of disease. Furthermore, neuroendocrine factors are thought to play a major role in gender-specific differences in development of certain disorders, including autoimmune/inflammatory diseases that have a two to tenfold higher incidence in females compared to males. Neuroendocrine factors can affect immune cells at the level of gene transcription but have also been shown to modify immune cell activity by interacting with intracellular molecules, resulting in modified ability of these cells to mount a potent immune response. In this review, we will consider various effects of the neuroendocrine system and its proteins on specific populations of immune cells and associated responses in host immunity against pathogens. We will further discuss how this modification of immune cell activity by the neuroendocrine system can contribute to susceptibility/severity of disease development.

Uterine natural killer cells: a specialized differentiation regulated by ovarian hormones

In adult females of many species, a transient population of natural killer (NK) cells appears in cycles within the uterine endometrium (lining). Appearance of these lymphocytes coincides with specific phases of the ovarian hormone cycle and/or early pregnancy. Studies in rodents, women, and pigs dominate the literature and suggest the uterine (u)NK cells are an activated subset sharing many but not all features with circulating or lymphoid organ-residing NK cells. During successful murine pregnancy, uNK cells appear to regulate initiation of structural changes in the feed arterial systems that support maternal endometrial tissue at sites of implantation and subsequent placental development. These changes, which reverse after pregnancy, create a higher volume arterial bed with flaccid vessels unresponsive to vasoactive compounds. These unique pregnancy-associated arterial changes elevate the volume of low-pressure, nutrient-rich, maternal arterial blood available to conceptuses. Regulation of the differentiation, activation, and functions of uNK cells is only partially known, and there is lively debate regarding whether and how uNK cells participate in infertility or spontaneous abortion. This review highlights the biology of uNK cells during successful pregnancy.

Endocrine regulation of menstruation

In women, endometrial morphology and function undergo characteristic changes every menstrual cycle. These changes are crucial for perpetuation of the species and are orchestrated to prepare the endometrium for implantation of a conceptus. In the absence of pregnancy, the human endometrium is sloughed off at menstruation over a period of a few days. Tissue repair, growth, angiogenesis, differentiation, and receptivity ensue to prepare the endometrium for implantation in the next cycle. Ovarian sex steroids through interaction with different cognate nuclear receptors regulate the expression of a cascade of local factors within the endometrium that act in an autocrine/paracrine and even intracrine manner. Such interactions initiate complex events within the endometrium that are crucial for implantation and, in the absence thereof, normal menstruation. A clearer understanding of regulation of normal endometrial function will provide an insight into causes of menstrual dysfunction such as menorrhagia (heavy menstrual bleeding) and dysmenorrhea (painful periods). The molecular pathways that precipitate these pathologies remain largely undefined. Future research efforts to provide greater insight into these pathways will lead to the development of novel drugs that would target identified aberrations in expression and/or of local uterine factors that are crucial for normal endometrial function.

Progesterone receptor requires a co-chaperone for signalling in uterine biology and implantation

Embryo implantation is absolutely dependent on the preparation of the uterus to the receptive stage and attainment by the blastocyst of implantation competency. Co-ordinated effects of progesterone and oestrogen are essential for these processes and determine the window of implantation. In rodents, a generalized stromal edema occurs before blastocyst attachment followed by uterine luminal closure. This leads to apposition of the blastocyst trophectoderm against the luminal epithelium and ultimately attachment. Progesterone is essential for luminal closure, which must occur for successful implantation. More importantly, progesterone is critical for almost every stage of pregnancy, including ovulation, fertilization, implantation, decidualization and pregnancy maintenance. Progesterone exerts its effects on target tissues primarily via nuclear progesterone receptor (PR) whose optimal activity is potentiated by an immunophilin co-chaperone, FK-506 binding protein 4 (FKBP52). While mice lacking PR are infertile due to complete failure of ovulation, fertilization, and implantation, female mice with targeted deletion of the Fkbp52 gene are infertile specifically because of implantation failure resulting from compromised uterine receptivity. This review highlights the evolution of knowledge about progesterone signalling during early pregnancy. Future studies are likely to provide a better understanding of FKBP52-PR signalling in promoting uterine receptivity for implantation and may reveal new targets for improving infertility.

Effects of implantation and early pregnancy on the expression of cytokines and vascular surface molecules in the sheep endometrium

Successful implantation is a highly coordinated process involving changes in cytokines, adhesion molecules, hormones, enzymes and growth factors. This study examines the expression of key cytokines and vascular surface molecules in the pregnant uterus of sheep around the time of implantation. Uterine tissues and uterine washings were collected from non-pregnant and pregnant sheep at 17-19 days post-coitus (dpc), 26-27 and 34-36 dpc. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of caruncular/placentomal tissues revealed that cytokines IL-2, IL-4 and IL-8, which were not detected in non-pregnant uterus, were induced more strongly at 26-27 dpc than at other stages of pregnancy tested. Cytokines LIF, IL-6, IL-10, TNF-alpha were also most highly expressed at 26-27 dpc, expression of them being lower at other time-points during early pregnancy and non-pregnancy. The cytokines IL-1beta, IFN-gamma and TGF-beta were expressed in all non-pregnant and pregnant tissues examined. Enzyme-linked immunosorbent assay (ELISA) performed on uterine washings clearly detected the presence of IL-1alpha protein at 26-27 and 34-36 dpc. Immunohistochemistry revealed that expression of vascular adhesion molecule VCAM-1 in endometrial endothelium was strongly induced at 26-27 dpc in the pregnant endometrium. Expression of CD5 on vascular endothelium was not induced in placentomal tissues until 26-27 dpc and was further increased by 34-36 dpc. These results demonstrate a dynamic change in a wide range of cytokines during early stages of pregnancy, with a critical period around 26-27 dpc. In addition, at 26-27 dpc, expression of the surface/adhesion molecules, CD5 and VCAM-1, is induced on vascular endothelium of the sheep endometrium, possibly as a direct consequence of the changed cytokine environment, and may be involved in directing the changes in leucocyte migration observed during pregnancy.

Decidualization of the human endometrial stromal cell: an enigmatic transformation

Changes in human endometrium are essential to allow the establishment of pregnancy. These changes are induced in vivo by progesterone, and include appearance within the tissue of a specific uterine natural killer cell, characterized by an abundant expression of CD56. Changes also occur in the stromal cells, which undergo a characteristic decidualization reaction. Decidualized stromal cells are derived from the fibroblast-like cells within the endometrium, which maintain their progesterone receptors in the presence of progesterone. Prolonged exposure to progesterone induces a rounded cell characterized by release of prolactin and insulin-like growth factor binding protein-1 (IGFBP-1), and expression of tissue factor. Additional changes include the secretion of interleukin (IL)-15, vascular endothelial growth factor, and surface expression of zinc dependent metalloproteinases such as CD10 and CD13. In vitro, elevated intracellular cAMP as well as progesterone is necessary for decidualization. In vivo, these conditions may be provided by progesterone from the corpus luteum, by prostaglandin E, a stimulator of adenyl cyclase, and relaxin, which has recently been shown to be a phosphodiesterase inhibitor. Given the co-distribution of uterine natural killer cells and decidualized stromal cells, a mutual interaction might provide the correct regulatory environment for successful implantation, and penetration of the maternal blood vessels by trophoblastic cells.

Inflammatory mediators and endometrial function--focus on the perivascular cell

Human endometrium has a unique vascular architecture that allows menstruation, the shedding of a well-vascularised tissue layer, with limited bleeding. Blood loss is controlled at least in part by constriction of the perivascular cells, myofibroblasts that surround the spiral arterioles and have contractile activity. These perivascular cells, which are coupled to endothelial cells by processes, are responsive to changes in progesterone levels and express chemokines, cytokines and prostaglandins (PG) crucial to the control of leukocyte entry into endometrium. In this location the chemokine interleukin-8 (IL-8) and prostaglandin E (PGE) will have synergistic effects on leukocyte entry. CD40 is also expressed on the perivascular cells. Activation of CD40 by CD40 ligand is known to increase COX-2 and IL-8 expression in endometrial fibroblasts. The likely source of CD40 ligand in the uterus is platelets. Thus ingress of platelets will up-regulate NFkappaB by activating CD40 and increase agents such as PGE which will stimulate further the ingress of platelets. There is thus the possibility of a spiralling inflammatory response. This response however, is normally modulated by progesterone raising the threshold of the NFkappaB pathway and in the presence of high progesterone levels activation of CD40 will be ineffective. When progesterone falls at the end of the ovarian cycle and the restrictions on activation are lost, the perivascular cells will respond, initiating leukocyte entry, vasoconstriction-vasodilatation cycles with associated hypoxia and consequent sloughing off of the endometrium. The perivascular cell in endometrium is pivotal in both menstruation and early pregnancy and we need to understand this cell better to devise more effective medical treatment for menstrual dysfunction.

Potential implications of chemokines in reproductive function: an attractive idea

Chemokines are a new family of cytokines specialised in attracting leukocytes, acting in physiological conditions and in pathological processes. A wide variety of cell types in response to exogenous irritants or endogenous mediators of the inflammatory reaction produce them. Pivotal parts of reproductive function are based on inflammatory like processes wherein different leukocytes subsets are recruited and activated to produce paracrine autocrine effects in which cytokines and growth factors are implicated. Since chemokines control leukocyte trafficking and belong to the cytokine superfamily, in this review we analyze the implications of these molecules and related cells in ovulation, embryonic implantation, menstruation, parturition and their role in pathological process such as preterm delivery, endometriosis, ovarian hyperstimulation syndrome and HIV infection.

Proliferation and apoptosis of fibroblasts and smooth muscle cells in rat uterine cervix throughout gestation and the effect of the antiprogesterone onapristone

OBJECTIVE

The purpose of this study was to determine the relative percentages of apoptosis and proliferation in fibroblasts and cervical smooth muscles throughout gestation and the effect of an antiprogesterone on these processes.

STUDY DESIGN

Rats were studied at days 5, 15, 18, and 21 and immediately postpartum (day 22). Apoptosis and proliferation as detected by specific immunohistochemistry quantitative morphometric analysis was performed. Onapristone, an antiprogesterone, was used to study effects of hormonal change on these processes in 16- and 19-day timed-pregnant rats.

RESULTS

Proliferation of fibroblasts and smooth muscle cells was highest in early pregnancy and decreased progressively, whereas apoptosis increased progressively in later pregnancy. Onapristone inhibited apoptosis.

CONCLUSION

Changes in cervical cellular turnover are initiated early in gestation and are under hormonal influence. Antiprogesterone inhibits cell death at days 16 and 19 of gestation.

Leukocyte infiltration and collagenolysis in cervical tissue from intrapartum sheep

Sheep uterine cervices and cervical mucus were heavily infiltrated by neutrophils during labour, whereas samples of cervices obtained from non-pregnant controls had no infiltrate. The neutrophilic infiltrate of the sheep uterine cervix at term was not homogeneously distributed throughout the organ: luminal mucus contained more neutrophils than tissues which, in turn, displayed a differential distribution, the superficial subepithelial layer being more heavily infiltrated than the deeper submucous layers. A widespread collagenolysis was observed in the sheep uterine cervix at term. The homogeneous morphological aspect of degradation of collagen fibres throughout the whole cervical stroma contrasted with the above-mentioned differential distribution of neutrophils. On the basis of previous reports showing that collagenolysis follows the leukocytic invasion of human and rat cervices at term, a possible role for the neutrophilic infiltrate of the sheep uterine cervix is discussed.

Prostaglandin E and F2 alpha concentration in the cervical mucus and mechanism of cervical ripening

OBJECTIVE

To study the mechanism of cervical ripening by determination of prostaglandin E (PGE) and F2 alpha (PGF2 alpha) concentrations in cervical mucus during the course of pregnancy.

STUDY DESIGN

Cervical mucus was collected from 99 pregnant women attending the mother care unit of the department. Women with sexual intercourse within the last 24 hours before sampling and subjects with bacterial vaginosis were analysed separately.

RESULTS

Eleven women had sexual intercourse within 24 hours before sampling. The concentration of PGE in their cervical mucus was high corresponding to 2000-4000 pg/mg w w lasting for a period of 10-12 hours postcoitally, whereas the levels of PGF 2 alpha only increased slightly. Bacterial vaginosis was accomplished by a slight but significant elevation of PGF2 alpha levels but only of a minor increment of the PGE values. The prostaglandin concentrations in the mucus from the remaining 68 women were for PGE 102.75 +/- 111.51 and for PGF2 alpha 97.54 +/- 82.48 pg/mg w w (mean +/- SD). Although the values were scattered the concentrations remained at approximately the same level throughout pregnancy and there was no tendency towards an increment during the last weeks of pregnancy when cervical maturation is apparent.

CONCLUSION

Cervical softening seems not to be accomplished by a massive local release of prostaglandins but rather the result of a number of different mechanisms more or less influenced by minor alterations of prostaglandin synthesis and release. Involved in these mechanisms are probably neutrophil-derived collagenases.

Why do women menstruate? Historical and evolutionary review

Theories regarding the significance of menstruation from the time of Aristotle to the present are reviewed, followed by a brief description of the evolutionary changes in the uterus. A specific duct for the transport of ova first appears in jawed fishes. Its important role in the evolution of internal fertilisation and the protection and nourishment of the embryo is followed through the vertebrate orders, amphibia, reptiles and mammals. The problems associated with the presence of a gamete or zygote of different genetic make up inside the maternal tract is stressed, and the mechanisms to overcome or modify the maternal inflammation reaction discussed. In egg laying reptiles and birds, the secretion of coverings around the embryo presumably shields the foreignness of the tissue, while in viviparous animals, the secretion of progesterone plays a major role in controlling the inflammatory reaction. In some mammals, for example the mouse, the invasiveness of the trophoblast is such that the blastocyst penetrates inside the wall of the endometrium. The stroma responds under the influence of progesterone, to undergo an implantation/decidual reaction which bears considerable resemblance to an inflammatory/granulation tissue reaction. A similar reaction occurs in women during the luteal phase in anticipation of a very invasive blastocyst. When there is no fertilisation the progesterone drops and the differentiated stromal tissue is shed with bleeding; menstruation.

MHC Class II positive cells and T cells in the equine endometrium throughout the oestrous cycle

The quantity and distribution of MHC Class II positive cells and T cells in the equine endometrium was investigated throughout the oestrous cycle. Significantly more MHC Class II positive cells were detected in the stratum compactum and stratum spongiosum of endometria from naturally cycling mares during the follicular than during the luteal phase of the oestrous cycle. Significantly more T cells were also detected in the stratum compactum, but not stratum spongiosum, of these mares during the follicular phase. Furthermore, there was a marked increase in the number of MHC Class II positive cells and T cells in the endometria of ovariectomised mares treated with oestradiol compared with progesterone. An increase in the expression of MHC Class II antigen by endometrial epithelial cells was also observed in mares treated with oestradiol and in some naturally cycling mares during the follicular phase.

Choriodecidual production of interleukin-8 and mechanism of parturition

Both prostaglandins and antiprogestagens can induce labour and ripen the cervix, but the mechanisms are unclear. The collagenases that bring about cervical ripening are neutrophil derived. We examined the potential of uterine tissues to control neutrophil attraction by measuring interleukin-8 production. Choriodecidual cells in culture produced substantial amounts of interleukin-8; release was inhibited by progesterone and stimulated by the antiprogestagen mifepristone. Interleukin-8 production was similar in cells from spontaneously delivered placentas and from those obtained at caesarean section. Since prostaglandin E and interleukin-8 have synergistic effects, we suggest that interleukin-8 activity is the final common step of prostaglandin and antiprogestagen action in parturition.

RU 486 mediated leukocytic inflammatory reaction at the utero-placental interface

Placentae obtained from RU 486 treated cynomolgus monkeys, with successful pregnancy outcome, could not be distinguished, by microscopic or macroscopic examination, from normal placental morphology of untreated females. However, circulating PAPP-A levels were markedly depressed in RU 486 treated (114.8 +/- 13.1 IU/l) than in control animals (477.2 +/- 150 IU/l), suggesting compromised placental physiology. Microscopic examination of placental tissue obtained from animals with fetal demise, after RU 486 administration, revealed pathological changes. When fetal demise occurred recently (less than 24 h), active villus destruction by infiltrating polymorphonuclear leukocytes was readily observed. Whereas aqueous extracts of placentae, whether obtained by cesarean section or spontaneous delivery, inhibited neutrophil elastase (HGE) activity, extracts of placenta being degraded by host phagocytic-proteolytic defense system were rich in HGE activity. Thus suggesting that parturition was not mediated by leukocyte lysosomal proteases, such as HGE, and that hemochorrially implanted placentae produce PAPP-A, a specific inhibitor of HGE. Administration of RU 486 decreased placental PAPP-A production and secretion, culminating with a neutrophilic infiltration into placental intervillous blood spaces, destruction of villus structure and fetal demise.

RU 486 induced suppression of placental neutrophil elastase inhibitor levels

After administration of RU 486 to pregnant cynomolgus monkeys, placental morphology varied from normal to pathological. In all cases (n = 5) circulating and placental PAPP-A levels were markedly suppressed by 76.0 per cent and 55.5 per cent, respectively. When fetal demise occurred within 24 h prior to caesarian section, morphological changes consistent with an active inflammatory (polymorphonuclear leukocytosis) reaction was readily observed at the utero-placental interface, degrading the chorionic villi. Whereas heparin-Sepharose fractionated aqueous extracts of placentae inhibited human neutrophil (or granulocyte) elastase (HGE) activity, extracts of placenta being degraded by host phagocytic-proteolytic defense system were rich in HGE activity. This study establishes: (1) the cynomolgus monkey as a model for PAPP-A studies, (2) that haemochorially implanted placentae produce PAPP-A, a heparin-binding inhibitor of HGE, (3) that administration of progesterone receptor antagonist suppressed placental PAPP-A synthesis, and (4) disrupted protease-protease inhibitor equilibrium at the feto-maternal interface. Thus supporting a role for progesterone in placental PAPP-A production and maintenance of a placental barrier against maternal phagocytic-proteolytic defenses.

Concentrations of immunoreactive leukotriene B4 in uterine lavage fluid from mares with experimentally induced and naturally occurring endometritis

Acute endometritis was induced in ovariectomized pony mares by infusion of a 1% solution of oyster glycogen. Maximum concentrations of immunoreactive leukotriene B4 in uterine washings coincided with the greatest rate of infiltration of neutrophils into the uterine lumen. Concentrations of immunoreactive leukotriene B4 decreased to basal levels 6 h after infusion and were unaffected by administration of ovarian steroids to ovariectomized mares. Uterine washings from mares with persistent endometritis did not contain significantly different concentrations of leukotriene B4 from genitally normal mares.