Aberrant positioning of trophoblast and lymphocytes in the feto-maternal interface with pre-eclampsia

Pregnancy represents the growth of an allograft where fetal trophoblast cells evade immune rejection and invade maternal tissue. There should be a balance between fetal trophoblast and maternal immune-responsive cells and alterations in the proportion of these cells may relate to pregnancy disorders. To test this, the decidual tissue of placental bed biopsies was examined and trophoblast cells and lymphocytes were quantified morphometrically; spiral arteries were classified as unchanged, transformed or affected by acute atherosis. Normal pregnancy (n=19) was characterized by the transformation of about one half of all spiral arteries within the placental bed. We found that 40% of all lymphocytes were CD56+ uterine NK cells and 60%, CD3+ T-lymphocytes; about 30% of these were CD8+ T cells. Intrauterine growth retardation in the context of preeclampsia (n=15) was accompanied by reduced trophoblast numbers within smaller and more tortuous arteries and an increase in the proportion of CD56+ uterine NK cells and CD8+ T lymphocytes in the decidua (70% of all CD3+ cells). In the case of pre-eclampsia without fetal growth retardation (n=14) no increase in CD56+ uterine NK cells was seen, while CD8+ T lymphocytes were significantly increased compared with the normal level (50% of all CD3+ cells). Fetal growth retardation is associated with poor transformation of spiral arteries and characterized by an increase of uterine NK cells. Symptoms of pre-eclampsia are independently associated with an increase in the cytotoxic T subset of decidual lymphocytes. Pre-eclampsia and related fetal growth retardation are seemingly caused by an enhancement of the maternal cytotoxic defence against the fetal allograft.     

Phenotypic Characterization of Macrophages in the Endometrium of the Pregnant Cow

Problem  Macrophages are recruited in large number to the interplacentomal endometrium of the cow during pregnancy. We evaluated whether endometrial macrophages also accumulate in placentomal regions of endometrium during pregnancy and whether endometrial macrophages are regionally differentiated.
Method of study  Interplacentomal endometrium and placentomes were subjected to dual-color immunofluorescence using CD68 as a pan-macrophage marker.
Results  CD68⁺ cells were abundant in stroma of the interplacentomal endometrium and caruncular septa of the placentomes. CD68⁺ cells were not present in fetal villi of the placentomes or in the interplacentomal chorion. Regardless of location, the majority of CD68⁺ cells also expressed CD14. In interplacentomal endometrium, CD68⁺CD11b⁺ cells were present in deeper areas of the stroma but not in shallow endometrial stroma. In caruncular septa of the placentome, CD68⁺ cells were negative for CD11b. CD68⁺ cells in the interplacentomal endometrium were negative for MHC class II while most CD68⁺ cells in caruncular septa were positive for MHC class II.
Conclusion  CD68⁺CD14⁺ macrophages present in the stroma of the interplacentomal endometrium and caruncular septa of the placentome are regionally differentiated with regard to expression of CD11b and MHC class II.     

Immunological relationship between the mother and the fetus

The immunological relationship between the mother and the fetus is a bi-directional communication determined on the one hand by fetal antigen presentation and on the other hand by recognition of and reaction to these antigens by the maternal immune system. There is evidence now that immunological recognition of pregnancy is important for the maintenance of gestation, and that inadequate recognition of fetal antigens might result in failed pregnancy. In contrast to HLA-A and -B Class I genes that are downregulated in human trophoblast cells, nonpolymorphic Class I molecules, e.g., HLA-G Class Ib, are expressed in extravillous cytotrophoblast and also in endothelial cells of fetal vessels in the chorionic villi as well as in amnion cells and amniotic fluid. The trophoblast does not induce transplantation immunity and resists NK- and CTL-mediated lysis in vitro. According to our present knowledge, HLA-G presents antigens for gamma/delta T cells and at the same time defends the trophoblast from cytotoxic effector mechanisms. Since polymorphic MHC is absent from the trophoblast, presentation of fetally derived antigens is unlikely to be MHC restricted. gamma/delta T cells recognize a distinct group of ligands with a smaller receptor repertoire than alpha/beta T cells. Most gamma/delta T cells recognize unprocessed foreign antigens without MHC. In the decidua gamma/delta TCR-positive cells significantly increase in number and the majority of decidual gamma/delta T cells are in an activated form due to recognition of conserved mammalian molecules on the trophoblast. Following recognition of fetally derived antigens, the immune system reacts with the setting in of a wide range of protective mechanisms. Many observations suggest that pregnancy is associated with an altered TH1/TH2 balance. Maternal immune response is biased toward humoral immunity and away from cell-mediated immunity that could be harmful to the fetus. Cytokines of maternal origin act on placental development. On the other hand, antigen expression on the placenta determines maternal cytokine pattern. Normal human pregnancy is characterized by low peripheral NK activity, and increased NK activity seems to play a role in spontaneous abortions of unknown etiology. In early human pregnancy the majority of uterine lymphocytes are CD56(bright) granulated NK cells, which do not express CD16 or CD3. In rodents and humans, uterine NK cells are under hormonal control. In early pregnancy they are enriched at sites where fetal trophoblast infiltrates the decidua. The dynamics of the appearance of uterine NK cells suggest that one of the functions of these cells is control of placentation. Another protective mechanism operating in favor of pregnancy is progesterone-dependent immunomodulation. Due to stimulation by fetally derived antigens, pregnancy lymphocytes develop progesterone receptors and in the presence of progesterone produce a mediator (PIBF) that, through altering the cytokine balance, inhibits NK activity and exerts an antiabortive effect in mice.     

IMMUNOLOGICAL RELATIONSHIP BETWEEN THE MOTHER AND THE FETUS

The immunological relationship between the mother and the fetus is a bi-directional communication determined on the one hand by fetal antigen presentation and on the other hand by recognition of and reaction to these antigens by the maternal immune system. There is evidence now that immunological recognition of pregnancy is important for the maintenance of gestation, and that inadequate recognition of fetal antigens might result in failed pregnancy. In contrast to HLA-A and -B Class I genes that are downregulated in human trophoblast cells, nonpolymorphic Class I molecules, e.g., HLA-G Class Ib, are expressed in extravillous cytotrophoblast and also in endothelial cells of fetal vessels in the chorionic villi as well as in amnion cells and amniotic fluid. The trophoblast does not induce transplantation immunity and resists NK- and CTL-mediated lysis in vitro. According to our present knowledge, HLA-G presents antigens for γ/δ T cells and at the same time defends the trophoblast from cytotoxic effector mechanisms. Since polymorphic MHC is absent from the trophoblast, presentation of fetally derived antigens is unlikely to be MHC restricted. γ/δ T cells recognize a distinct group of ligands with a smallerreceptorrepertoire than α/β T cells. Most γ/δ T cells recognize unprocessed foreign antigens without MHC. In the decidua γ/δ TCR-positive cells significantly increase in number and the majority of decidual γ/δ T cells are in an activated form due to recognition of conserved mammalian molecules on the trophoblast. Following recognition of fetally derived antigens, the immune system reacts with the setting in of a wide range of protective mechanisms. Many observations suggest that pregnancy is associated with an altered TH1/TH2 balance. Maternal immune response is biased toward humoral immunity and away from cell-mediated immunity that could be harmful to the fetus. Cytokines of maternal origin act on placental development. On the other hand, antigen expression on the placenta determines maternal cytokine pattern. Normal human pregnancy is characterized by low peripheral NK activity, and increased NK activity seems to play a role in spontaneous abortions of unknown etiology. In early human pregnancy the majority of uterine lymphocytes are CD56 bright granulated NK cells, which do not express CD16 or CD3. In rodents and humans, uterine NK cells are under hormonal control. In early pregnancy they are enriched at sites where fetal trophoblast infiltrates the decidua. The dynamics of the appearance of uterine NK cells suggest that one of the functions of these cells is control of placentation. Another protective mechanism operating in favor of pregnancy is progesterone-dependentimmunomodulation. Due to stimulation by fetally derived antigens, pregnancy lymphocytes develop progesterone receptors and in the presence of progesterone produce a mediator (PIBF) that, through altering the cytokine balance, inhibits NK activity and exerts an antiabortive effect in mice.     

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

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

Development of the implantation chamber in the pregnant bitch

Uteri taken from 25 bitches at various times during the early stages of pregnancy were studied cytologically to determine how the implantation chamber developed and how fetal-maternal relations were established. On day 13 after the end of estrus, knobs of trophoblastic syncytium formed and became wedged between cells of the uterine luminal epithelium. The syncytium quickly spread along the uterine lumen and into the mouths of the glands, dislodging and surrounding maternal cells. As invasion continued trophoblastic villi, consisting of cores of cytotrophoblast covered by a continuous layer of syncytium, penetrated deeper into the endometrium. The syncytium spread to surround maternal vessels and decidual cells. By day 26 the trophoblast had extended down to the large lacunae. Here syncytial trophoblast covering tips of the villi degenerated, leaving cytotrophoblast exposed to the necrotic zone. These cells possessed characteristics of absorbing cells. Hematomas were formed by focal necrosis of fetal and endometrial tissue at the poles of the implantation sites. Large pools of extravasated blood accumulated and red blood cells were phagocytized by surrounding trophoblastic cells. Therefore, the endotheliochorial relationship in the canine placenta appeared to be established by syncytial trophoblast invading a cellular endometrium. In the necrotic zone and hematomas, cellular trophoblast may have lost its syncytial covering, but elsewhere maternal vessels and decidual cells in the placenta were in direct contact only with syncytial trophoblast.     

Implantation in the rhesus monkey: Initial penetration of endometrium

A series of peri-implantation stages of the rhesus monkey has been collected; these range from preimplantation blastocysts through initial implantation to early villus formation. The three earliest postimplantation specimens encompass the stages of penetration into and through the uterine luminal epithelium and into endometrial blood vessels. The day of pregnancy was established by radioimmunoassay of estrogen (E) levels to determine the prevulatory E peak, and in each instance the embryo was examined to determine the extent of development. The conceptus collected on day 9.5 of pregnancy was the earliest implantation stage; it ballooned above a depression in the endometrium to which it was firmly attached. A column of syncytial trophoblast penetrated into the uterine epithelium to the basal lamina of the latter. The syncytial trophoblast shared junctional complexes with the uterine epithelial cells to which it was apposed at the margin of the site of epithelial penetration. Basal to the apical junction complexes, processes of syncytium indented uterine epithelial cells. Several epithelial cells had been partially isolated and surrounded by flanges of syncytial trophoblast. In the next specimen, at 10.0 days after ovulation, the uterine epithelium had initiated the epithelial plaque reaction. The trophoblast had extended along the residual basal lamina of the uterine epithelium and into the neck of an adjacent uterine gland. Cytotrophoblast was abundant in the central region of the implantation site, and was intermixed with syncytium which formed the majority of the peripheral trophoblast. In several places clefts had formed in the syncytial trophoblast; these clefts were lined with microvilli, had intermicrovillous caveolae, and consequently more closely resemble the trophoblast that eventually lines the intervillous spaces than the trophoblast involved in initial invasion. In the day-10.5 specimen, in addition to prelacunar clefts, lacunae containing maternal blood were present for the first time. The basal lamina was penetrated in many places, and syncytial trophoblast was interposed between maternal endothelial cells of the underlying vessels. It was concluded that syncytial trophoblast is the first tissue to penetrate the uterine luminal epithelium; that the basal lamina of the uterine luminal epithelium, but not the basal lamina of endothelium, constitutes a temporary barrier to trophoblast penetration; that invasion is accomplished with less destruction of maternal tissue than previously suggested; and that the rapid superficial growth of the placenta is made possible by the early tapping of the endometrial vessels.     

Biology and pathology of the uterine microenvironment and its natural killer cells

Tissues are the new frontier of discoveries in immunology. Cells of the immune system are an integral part of tissue physiology and immunity. Determining how immune cells inhabit, housekeep, and defend gut, lung, brain, liver, uterus, and other organs helps revealing the intimate details of tissue physiology and may offer new therapeutic targets to treat pathologies. The uterine microenvironment modulates the development and function of innate lymphoid cells [ILC, largely represented by natural killer (NK) cells], macrophages, T cells, and dendritic cells. These immune cells, in turn, contribute to tissue homeostasis. Regulated by ovarian hormones, the human uterine mucosa (endometrium) undergoes ~400 monthly cycles of breakdown and regeneration from menarche to menopause, with its fibroblasts, glands, blood vessels, and immune cells remodeling the tissue into the transient decidua. Even more transformative changes occur upon blastocyst implantation. Before the placenta is formed, the endometrial glands feed the embryo by histiotrophic nutrition while the uterine spiral arteries are stripped of their endothelial layer and smooth muscle actin. This arterial remodeling is carried out by invading fetal trophoblast and maternal immune cells, chiefly uterine NK (uNK) cells, which also assist fetal growth. The transformed arteries no longer respond to maternal stimuli and meet the increasing demands of the growing fetus. This review focuses on how the everchanging uterine microenvironment affects uNK cells and how uNK cells regulate homeostasis of the decidua, placenta development, and fetal growth. Determining these pathways will help understand the causes of major pregnancy complications.Keywords: Natural killer cells, Uterine microenvironment, Pregnancy, Decidua, uNKSubject terms: Immunology, Cell biology     

Pregnancy outcome in human couples with recurrent spontaneous abortions: HLA antigen profiles; HLA antigen sharing; female serum MLR blocking factors; and paternal leukocyte immunization

Critical features of the trophoblast for immune protection in the mother are: (1) its resistance to cytotoxic lymphocytes and antibodies; (2) it forms a physical barrier to immune effector cells, but not antibody, from reaching the fetus; (3) it signals the migration of suppressor and other functionally hyporesponsive lymphocytes into the uterine decidua and uterine lymphatics; (4) it promotes the production of maternal serum MLR (mixed lymphocyte reaction) blocking antibody with paternal antigen specificity. Some of these immunological features are lacking in women with recurrent abortions of immune etiology. Eleven women who aborted an additional time after immunization with paternal leukocytes were compared with 14 women who delivered infants at term post-immunization. It was found that those who aborted: (1) had HLA antigen profiles that did not differ significantly from those of control fertile couples or from observed antigen frequencies in North American Caucasians; (2) shared more HLA A, B, D/DR, and MT antigens with their spouses than controls; (3) were not more hyporesponsive in MLR to paternal antigens pre- and post-immunization when compared to controls; (4) failed to develop female serum MLR blocking factors post-immunization; (5) failed to develop humoral alloantibodies to B-cell alloantigens; (5) had lymphocytes in the uterine decidua mantling the conceptus and in the uterine lymphatics that were reactive/cytotoxic to paternal stimulating alloantigens. These results are in sharp contrast to the immunodynamics of peripheral blood leukocytes and decidual leukocytes to paternal alloantigens in women who delivered infants at term post-immunization.     

Evidence of specialized leukocyte-vascular homing interactions at the maternal/fetal interface

In normal pregnancy, the maternal immune system fails to reject the fetus or the placenta as an allogeneic graft. We hypothesize that specialized mechanisms of leukocyte recruitment might limit access of circulating maternal immune cells to the maternal/fetal interface. During the critical period of initial trophoblast invasion there is an elegantly orchestrated progression of leukocyte homing events in the decidua basalis, associated with highly regulated expression of vascular addressins and segregation of specialized leukocyte subsets into well-defined decidual microdomains. Neutrophils are limited to the region of necrosis associated with enzymatic digestion at the leading edge of the invading trophoblast, where an almost linear array of maternal blood vessels displays the neutrophil ligand E-selectin. Cells with the phenotype of monocytes but expressing alpha4beta7 integrin are localized in the blood vessels of the specialized "vascular zone", which display the unusual combination of P-selectin (partially associated with platelets) and the alpha4beta7 ligand mucosal vascular addressin-1 (MAdCAM-1). Granulated metrial gland cells (alpha4+beta7-, probably alpha4beta1+) constitute a well-defined cluster positioned in the central decidua basalis around venules prominently expressing the alpha4beta1 ligand VCAM-1 (but not MAdCAM-1). T and B lymphocytes are rare. Our results suggest that selective mechanisms for regulating leukocyte access, associated with microdomain specialization within the decidua basalis, may play a fundamental role in immune regulation during the invasive period of placental development.     

Collagen types I, III and IV in the placentome and interplacentomal maternal and fetal tissues in normal cows and in cattle with retention of fetal membranes

The increase in uterine mass during pregnancy requires the establishment of sufficient blood supply to and strong supportive elements within the uterus. These needs are correlated with the remodelling and production of ECM materials. Therefore, placentomes and interplacentomal parts of the uterine walls and adherent allantochorion were collected from 45 cows at slaughter. Additional placentomes were obtained from 5 cows at premature cesarean section and at term in 5 cows releasing their fetal membranes in time or in 5 animals with retention of the fetal membranes, i.e. in total 60 pregnancies. Unfixed cryostat sections from 4 animals per month of pregnancy and 5 animals per peripartal group (in total 51 pregnancies) were used to immunolocalize collagen types I, III, and IV by an indirect FITC method. Collagen types I and III co-localize within the uterus. The tensile strength of the pregnant uterus is mainly represented by high contents of collagen type I within the allantochorion and subepithelial endometrial and subserosal meshes. Chorionic villi are fixed within caruncular crypts by two mechanisms: crypt openings are narrow and supplied with thick edges containing collagen types I and III. Collagen type IV contributes to all basement membranes and encloses connective tissue cells within the maternal crypt stroma, the stratum compactum and the perimetrial connective tissue. At term, fetal membranes and placentomes are edematous and at the light-microscopic level no distinct differences are visible between connective tissue fibers of placentomes from animals retaining the fetal membranes and those releasing them in time. In conclusion, collagen types I, III and IV exhibit type- and location-specific distribution patterns within the uterus of the pregnant cow. These may additionally be influenced by the stage of pregnancy, thus reflecting the dynamic processes at the stromal level.     

Fas and Fas-ligand are expressed in the uteroplacental unit of first-trimester pregnancy

PROBLEM: Fas and Fas-ligand (FasL) are thought to provide a strategy for reducing graft rejection in immunologically 'privileged' tissues by controlling injurious lymphocyte reactions. As the uteroplacental unit is often defined as an immune-privileged site, we investigated the expression of Fas and FasL in this tissue in the first trimester of pregnancy. METHOD OF STUDY: Western blotting, immunohistochemistry, and double immunofluorescence were used for this examination. RESULTS: Western blotting with purified first-trimester trophoblast cells revealed one specific band for FasL. The presence of FasL on different trophoblast populations could be confirmed by immunohistochemistry and double immunofluorescence. In the villous part of the placenta, FasL is mostly located on cytotrophoblast cells with no access to maternal blood flow, whereas in trophoblast-invaded uterine tissue, interstitial trophoblast cells, which are in close contact with maternal leukocytes, revealed a strong signal for FasL, but no staining for Fas on these cells. However, Fas was found on CD45+ maternal leukocytes. CONCLUSION: Based on our experimental findings, we speculate that the abundant presence of FasL on trophoblast cells within the maternal decidua may play an important role in the maintenance of immune privilege in the pregnant uterus by endowing fetal trophoblast cells with a defense mechanism against activated maternal leukocytes, whereas in the villous part of the placenta, the Fas FasL system seems to be involved in the regulation of placental growth.     

Expression of CD5, a lymphocyte surface antigen on the endothelium of blood vessels

CD5 is a lymphocyte surface antigen considered to be a pan-T cell marker although it is also expressed on a small population of B cells. In this report we present evidence that four different monoclonal antibodies specific for the CD5 antigen also recognize a molecule present on the endothelium of blood vessels in certain regions (placentomes) of the pregnant sheep uterus. The identity of the CD5 antigen on the endothelium with that expressed on T lymphocytes was confirmed by molecular mass analysis of the CD5 antigen in membrane extracts of lymphocytes, thymocytes and placentomes which showed that all three antigens have an apparent molecular mass of 67 kDa. Possible implications of this finding in relation to the function of the CD5 molecule and lymphocyte migration are discussed.     

Functional modifications of the CD4+ and the CD8+ subset due to maternal serum

Numerous experiments have been performed to try to explain the successful gestation of the semiallogeneic mammalian fetus in the immuno-competent mother. A popular hypothesis is that localized intra uterine suppression mediates the immune response and contributes directly to the survival of the fetus. Suppressive factors synthesized at the fetomaternal interface may be transported by the bloodstream and be found in the retroplacental and peripheral blood circulation. In this report we aim to study these modulating factors by exposing a proteinaceous antigen (Candidine or human mono nuclear cells) to unrelated human lymphocytes in the presence of a pool of maternal serum, retroplacental (MAT SR) or peripheral (MAT SP), or to a pool of male or calf serum (MALS or CS). A significant downregulation of the candidine mediated lymphocytic stimulation was observed in the case of the maternal serum. In order to further characterize this inhibition, a quantitative evaluation of the expression of the CD4 and CD8 positive subpopulations was performed. A selective inhibition of the CD4 positive subset was observed. In the PHA stimulation assay in the presence of maternal serum there was an inhibition of the thymidine uptake of unrelated lymphocytes. When studying the different subsets which were stimulated in the presence of maternal serum and control media it was shown that the CD4 positive subpopulation remained unchanged while there was a slight inhibition of the CD8 positive subset in the first case (maternal serum treated). The same CD4 positive inhibitive property of maternal serum was observed when a neoplastic cell line (HUT cells) was used as target for candidine in a stimulation test. This CD4 inhibited expression remained constant as long as the maternal serum was renewed. Maternal lymphocytes however remained resistant to the inhibitive action of maternal serum and did not show any change in their CD4 and CD8 positive subpopulation. By investigating the different blood components, it was shown that the suppressive factor was included in the IgG fraction and synthesized at the placental level. Appearing quite early during the gestation (at the 5-6th week), this factor was vanishing 2 weeks after the delivery.     

Penetration of the uterine epithelium during implantation in the rabbit

The structure of interacting trophoblast and uterine epithelium was studied in 16 rabbits from seven days zero hours to seven days 20 hours post coitus. The most common type of penetration of the uterus by the trophoblast consisted of a peg from a trophoblastic knob that extended to the basal lamina of the uterine luminal epithelium and was bordered by uterine epithelial cells with which it shared junctional complexes. In early implantation sites there was direct evidence of fusion of the syncytial trophoblast with apical ends of individual uterine epithelial cells. Since no evidence of epithelial dissociation or mechanical intrusion of trophoblast between epithelial cells was found, it is suggested that fusion is the normal method of epithelial penetration by the trophoblast in the rabbit. The cytoplasm of the fused uterine cells was apparently converted into syneytium of the trophoblastic knob. Subsequent to formation of the trophoblastic peg, penetration of the basal lamina and of maternal blood vessels occurred, and the attached trophoblastic knobs increased in width. At later stages when symplasma formation by the uterine epithelium was extensive, fusion included trophoblast between knobs. Since the penetration peg is formed by fusion of trophoblast with uterine epithelium, the cell membrane first associated with the maternal connective tissue is of maternal origin. However, new membrane formed after fusion would be expected to have histocompatibility factors from both the trophoblast and the fused maternal epithelial cells.     

Trophoblast-decidual cell interactions and establishment of maternal blood circulation in the parietal yolk sac placenta of the rat

Implantation sites from rats were studied on days 6, 7, and 8 of pregnancy to determine the sequence of events in the formation of blood spaces in the trophoblast that is part of the parietal wall of the yolk sac placenta and to determine how trophoblast gains access to maternal blood. The maternal blood flowing through these spaces is the source of nutrients that reach the embryo via the visceral endoderm. Tissues were prepared for light microscopy, scanning electron microscopy, and transmission electron microscopy. Trophoblast blood spaces are derived from the lateral intercellular spaces of trophoblast cells and are present in a collapsed condition until day 8, when maternal vessels are tapped by trophoblast. These spaces then contain circulating maternal blood, and trophoblast cells reflect adaptations for metabolic exchange including thinning of trophoblast covering Reichert's membrane and the appearance of numerous fenestrations, with and without diaphragms, in the areas where trophoblast is attenuated. Between days 6 and 7 decidual cells appear to form a barrier between the maternal circulation and trophoblast. On day 7, however, decidual cell processes penetrate the residual uterine luminal epithelial basal lamina, and then the decidual cells that are juxtaposed to trophoblast undergo degradative changes that resemble apoptosis. There is condensation of cytoplasmic contents, fragmentation of the cells, and phagocytosis of the fragments by trophoblast. Some decidual cells are interposed between endothelial cells in the walls of maternal vessels as early as day 7. Trophoblast may gain access to the maternal vessels by replacing decidual cells or by direct imposition of trophoblast cell processes between endothelial cells.     

Comparison of fetal and maternal inflammatory responses in the ovine placenta after experimental infection with Chlamydophila abortus

Placentae from 13 pregnant ewes infected intravenously with Chlamydophila abortus, together with placentae from nine uninfected control ewes, were examined at 14, 21 or 28 days post-inoculation (p.i.). Chlamydial inclusions were present in the trophoblast at 14 days p.i. and were widespread by 21 days p.i. Chorioallantoic lesions (oedema, arteritis and thrombosis) were severe at 28 days p.i., the changes being particularly marked in the membrane surrounding placentomes. Lymphocytes constituted only a small proportion of the cellular infiltrate in the chorioallantois; neutrophil infiltration of the chorionic surface was evident where the trophoblast layer had sloughed, whereas macrophages represented the predominant cell type in the deeper stroma. In contrast, on the maternal side of the placenta, chlamydial inclusions were sparse at all timepoints, and even at 28 days p.i., lesions were restricted to focal endometritis at the placentomal limbus and occasional foci of septal necrosis. T lymphocytes were numerous within endometrial and septal lesions, the infiltrate consistently containing more CD8(+) than CD4(+) cells. The fetal response to chlamydial invasion of the placenta was innate in character, whereas the maternal response appeared to represent an acquired, chlamydia-specific immune response.     

No evidence for apoptosis of decidual leucocytes in normal and molar pregnancy: implications for immune privilege

Complete hydatidiform moles are totally paternally derived and represent complete allografts that might be expected to provoke maternal immune rejection. Our previous and other studies have shown expression of Fas by increased numbers of activated decidual CD4(+) T cells in both complete and partial molar pregnancy as well as increased FasL(+) expression by molar trophoblasts compared with trophoblasts in normal pregnancies. As the Fas/FasL system represents a major apoptotic pathway that can play a role in immune privilege, the aim of this study was to investigate whether apoptosis of decidual immune cells, particularly T cells, could be responsible for maternal immune tolerance in molar pregnancy. Using terminal deoxynucleotidyl transferase (TdT)-mediated nick end-labelling (TUNEL), a significant increase in TUNEL(+) cells was demonstrated in decidua associated with partial (P = 0.0052) and complete (P = 0.0096) hydatidiform mole compared with normal early pregnancy. Co-labelling immunoperoxidase studies showed that the TUNEL(+) cells in both normal and molar pregnancies were not activated CD45RO(+) immune cells, CD3(+) T cells, CD56(+) uterine natural killer (NK) cells or CD14(+) CD68(+) macrophages. Double immunohistochemical labelling with antiactive caspase-3 and leucocyte markers confirmed the lack of leucocyte apoptosis. Double immunostaining with anticytokeratin to detect trophoblast and M30 CytoDeath, which detects a neoepitope of cytokeratin 18 revealed after caspase-mediated cleavage, revealed apoptotic extravillous trophoblast cells within decidual tissue. We conclude that there is no evidence that apoptosis of decidual leucocytes plays a role in maintaining maternal tolerance in either normal or molar pregnancy.