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The authors delineate seven quantum leap forward and, or revolutions having occurred during the 20th century in the understanding of the physiopathology of preeclampsia. First the discovery of the inflatable arm band permitting to measure blood pressure in 1896. Second, the discovery that eclamptic (convulsions), and later "pre"eclamptic (proteinuria) women presented hypertension in 1897 and confirmed in 1903, discovery of the hypertensive disorders of pregnancy. Third, the eight major textbooks published all along the 20th century by delineating risk factors of preeclampsia with the concept of "preeclampsia, disease of primigravidae". Fourth, the discovery in the 1970's that human trophoblast implantation was far deeper than in other mammalian species. Fifth, and a major step forward, description at the end of the 1980's that the maternal syndrome in preeclampsia (glomeruloendotheliosis, HELLP syndrome, eclampsia) could be unified in a global endothelial cell inflammation. Sixth, the epidemiological descriptions in the 1970-1990's that indeed preeclampsia was a disease of first pregnancies at the level of a couple ("primipaternity concept"), leading to an explosion in immunological research in the last decade, beginning in 1998. Seventh and finally, in the search for the "factor X" explaining the vascular inflammation in preeclamptic women (inositol phospho glycans P-type were described in 2000, while soluble Flt-1 and S-endoglins have been clearly predicted since 1997). The majority of the seeds or findings have been grounded or realized in the 20th century. Indeed, for preeclampsia, the 20th century has been le "Siècle des Lumières" (the Enlightments)., (Copyright © 2018 International Society for the Study of Hypertension in Pregnancy. Published by Elsevier B.V. All rights reserved.)

The uterine luminal environment was explored with regard to interleukin-18 (IL-18) and mannose-binding lectin (MBL) and the possibility that the procedure of flushing the uterine cavity would optimize the physiological initial pseudo-inflammatory uterine reaction. Uterine flushings were performed among 175 IVF/intracytoplasmic sperm injection (ICSI) patients at the time of oocyte retrieval and the cycles were compared with a control group matched for age, number of previous attempts and type of assisted reproductive procedure (IVF or ICSI) in which no flushing were performed (n = 175). Samples collected were divided into two groups according to the presence/absence of endometrial cells in samples. IL-18 and MBL expressions were explored by enzyme-linked immunosorbent assay. Implantation rates were significantly higher in those patients who underwent the uterine flushing compared with controls (P = 0.04). Luminal concentrations of IL-18 and MBL were higher if endometrial cells were present in flushings, suggesting endometrial origin of the secretion. Both concentrations of MBL and IL-18 were higher in patients with unexplained infertility compared with patients involved in IVF/ICSI for male or tubal infertility (P = 0.005 and 0.02, respectively). The exploration of the endoluminal environment before oocyte retrieval may enhance pregnancy rates and show distinct features in patients with unexplained infertility.

Several reports have described an association between the presence of soluble human leukocyte antigen G (sHLA-G) in human embryo culture supernatants (ES) and implantation success. However, not all studies agree with these findings. To further document this debate, a multicentre blinded study was performed to investigate, on a large number of IVF ES and ICSI ES, whether sHLA-G is a useful criterion for embryo selection before transfer. A total of 1405 ES from 355 patients were collected from three assisted reproductive technique (ART) centres and evaluated for their sHLA-G content in a single laboratory, using a chemiluminescence enzyme-linked immunosorbent assay. In only one centre was a significant association between sHLA-G-positive ES and successful implantation established (P = 0.0379), whereas no such association was observed in the other centres. It was found that the percentages and concentrations of sHLA-G-positive ES varied between centres, depending on culture media and ART conditions. The percentage of sHLA-G-positive ES was significantly higher in IVF ES than ICSI ES (P < 0.001 and P < 0.01 for two centres). These data demonstrate that substantial variations of sHLA-G content in ES occur between different ART centres, highlighting the influence of several technical parameters that differ from one centre to another.

The introduction to this review discusses briefly why immunology, perceived as difficult by assisted reproduction technology clinicians, need nevertheless be envisaged as a central actor in the reproduction process, and how the maternal immune system, initially perceived as a threat to the fetoplacental unit, is in fact utterly necessary for successful pregnancy. The key cells in such a process are uterine natural killer cells, which can act as friend or foe to the fetus, but are now known to play a key role in local vasculogenesis. As an ultimate consequence in cases of dysfunction/dysregulation, these factors result in implantation failure, abortion or pre-eclampsia.

This article explains why we have had to come to a central role for innate immunity rather than the threat of maternal rejection of the foetal allograft. We encompass briefly the role of inflammation in implantation, not only for invasion adhesion, but also to prepare future "tolerance". In this context, we envisage the role of TWEAK and complement.

In a brief introduction, this review states why the presence of immune cells at the interface poses problems for an immunologist (Medawar paradigm). Different types of placentation are then discussed, and the various interactions with leukocytes, the extreme being with the equids where a certain degree of 'attack' is often seen. The limits of animal models when dealing with the human situation are emphasized. It is then stated why the various phases of pregnancy are different, and an analysis made of the cellular movements at the implantation, peri-implantation, immediate post-implantation and resorption windows in rodents. Details of the cellular components involved are given, as are hints for the human situation. The Th1/Th2 paradigm is described, with clinical examples, and its limits. Thus, the newly appraised dual role of natural killer (NK) cells is discussed, with examples in rodents and in humans (pre-eclampsia, implantation failure, abortion systems). Clinical data on the IL-12/IL-18/NK tripod and implantation failure in humans are detailed.

In a brief introduction, this review states why the presence of immune cells at the interface poses problems for an immunologist (Medawar paradigm). Different types of placentation are then discussed, and the various interactions with leukocytes, the extreme being with the equids where a certain degree of 'attack' is often seen. The limits of animal models when dealing with the human situation are emphasized. It is then stated why the various phases of pregnancy are different, and an analysis made of the cellular movements at the implantation, peri-implantation, immediate post-implantation and resorption windows in rodents. Details of the cellular components involved are given, as are hints for the human situation. The Th1/Th2 paradigm is described, with clinical examples, and its limits. Thus, the newly appraised dual role of natural killer (NK) cells is discussed, with examples in rodents and in humans (pre-eclampsia, implantation failure, abortion systems). Clinical data on the IL-12 /IL-18/NK tripod and implantation failure in humans are detailed., (Copyright 2007 Reproductive Healthcare Ltd, Duck End Farm, Dry Drayton, Cambridge CB23 8DB, UK. Published by Elsevier Ltd. All rights reserved.)

Mechanisms of HIV-1 in utero mother-to-child transmission (MTCT) protection provided by AZT are not completely understood. The placental cytokine network is involved in the control of HIV-1 in utero transmission but the effect of AZT on this network is unknown. To evaluate the effects of AZT on placental cytokine expression, the chorionic villi from HIV-1 uninfected women term placentae were cultured with 0, 100, and 2,000 ng/ml AZT. Tissue fragments were harvested at days 1, 4, and 7 to determine the level of cytokine mRNA by real-time RT-PCR. The viability and morphology of the placental histocultures were monitored by the expression of beta-human chorionic gonadotropin (beta-hCG) gene, lipopolysaccharide (LPS) activation, and microscopic examination. AZT at 2,000 ng/ml significantly down-regulated TNF-alpha mRNA expression at day 1 and day 4, but had no effect on beta-hCG, stromal cell-derived factor 1 (SDF-1), and IL-10 gene expression. AZT did not induce any deleterious impact on placental tissue structure. Furthermore, activation of chorionic villi by LPS for 24 h up-regulated IL-10 and TNF-alpha mRNA expression. Down-regulation of TNF-alpha mRNA could represent a mechanism through which AZT can decrease the risk of HIV-1 MTCT, in addition to its direct effect on HIV-1 replication.

We aimed to set up and validate a new in vitro model of placental histocultures, for the evaluation of cytokine and chemokine profiles of the placental environment, over a long culture period. Micro-explant cultures from 6 early and 6 term placentae were set up on collagen sponge gel supports at a liquid/air interface. At various times during culture, we analyzed tissue morphology and cell death by microscopy and quantified beta-hCG production and mRNA levels for beta-hCG and insulin-like 4 (INSL4). Levels of IL-6, LIF, TNF alpha, IL-10, IFN-gamma, IL-16 and RANTES in the medium were measured by ELISA on days 1, 4 and 7 of culture. SDF-1 mRNA expression was determined by real-time PCR at the same time points. Histocultures from early and term placentae remained viable until day 10. High levels of IL-6 and LIF production, low levels of TNF alpha, IL-10 and IFN-gamma production and significant SDF-1 expression were observed. These data indicate that placental histoculture is a suitable and reliable in vitro model for studying the placental environment., ((c) Elsevier Ltd. All rights reserved.)

Villous trophoblast cells (TC) obtained from first trimester and term human placentae after trypsin/Percoll gradient isolation were immunodepleted of contaminant cells. The level of purity was assessed by the intracellular expression of the pan trophoblast marker cytokeratin-7 (CK7) and comparisons were made with the GB25 trophoblast-specific (cytotrophoblast+syncytiotrophoblast) cell surface marker. The presence of contaminating cells was traced with intracellular vimentin, or cell surface CD2, CD36, and CD163 markers and evaluated by flow cytometric analysis. The pattern of CK7 expression by trophoblast cells was also analyzed by immunofluorescence microscopy. Most batches of TC from first trimester or term placentae (92+/-3% and 96+/-2%, respectively) showed a high percentage of CK7 expressing cells, with less than 2% contaminating vimentin positive cells. In some batches of TC with a lower percentage (65+/-4%) of CK7-expressing cells, no vimentin was found, but a low percentage of CD36-expressing cells was evidenced, with no presence of CD2, and/or CD163-expressing cells. The intracellular CK7 signal correlated significantly with that of GB25 (p<0.05) cell surface expression in TC of term placentae. The choriocarcinoma BeWo and Jar cell lines also showed high levels (>92%) of CK7-expressing cells. Conversely, the control U87 astrocytoma cell line showed a high percentage (>90%) of vimentin but no CK7-expressing cells. These results provide evidence that the mutually exclusive pattern of intracellular CK7/vimentin expression of human TC can be used for evaluation by flow cytometry of the purity of primary human trophoblast cells.

Pregnancy is controlled primarily, though not exclusively, by a delicate equilibrium between locally acting growth factors and cytokines, some under steroid control. The hypothesis considered here is that stress is able to influence the equilibrium between cytokines and thus lead to abortions or implantation failure. We thus detailed the studies on that topic in order to explore the psycho-neuro-immunological mechanisms concerned. The duration of stress, the patient's strategy for coping with this and the social context might be able to produce some opposite immunological effects. Thus, the link between stress and the immunological events induced is complex, and much care is needed for such patients.

Introduction: To assess ultrasonic data in the context of repeated failure of implantation in assisted reproduction medicine., Materials and Methods: We reviewed ultrasonic data (uterine score at follicular and luteal phase). The same ultrasound exploration was repeated for two consecutive cycles to assess the changes in abnormalities observed and compare findings in 16 patients with repeated failure of implantation and in 14 controls. The controls were women who became pregnant within the three months following the exploration. We then introduced acetylsalicylic acid and prednisolone as first line treatment and nitroglycerin as second line treatment to measure the effects induced in 14 pathological uterine scores., Results: The score obtained under hormonal treatment was representative of other cycles (r = 0.812, p < 0.0014). The score was significantly lower and the luteal uterine artery pulsatility index was significantly higher in the repeated failure group than in the control group (p < 0.0001 and p = 0.008 respectively). For the 14 patients, treatment improved the uterine score in 8 with acetylsalicylic acid and prednisolone and in 4 with nitroglycerin. Two patients did not respond to treatment. Concerning the effect of therapy, of 14 patients, 8 had an improved uterine score with A + P, and with T; 2 patients did not respond to any treatment., Conclusion: The uterine score and luteal artery pulsatility index may be valuable tools for patients with implantation failure who all do not respond to the same therapy.

The immunotrophic theory was enunciated by Tom Wegmann. Since then, the involvement of cytokines in implantation and materno-fetal tolerance has emerged as a central topic in reproductive immunology. This brief survey covers the historical background leading to the specification of the crucial role of cytokines at the feto-maternal interface, and the present known patterns of their function. Focus is addressed to the most recent concept, e.g. pregnancy as a Th2 phenomenon (the immune response of the mother is biased towards the production of anti inflammatory cytokines, amongst them IL-10 which suppress inflammatory responses). A brief description of the role of inflammatory cytokines in implantation is presented to explain why it does not fit into such a scheme, and other recent data, for example on gamma interferon, also fails to accord with the Th2 phenomenon.

A low-molecular-weight material present in human placental supernatant (lymphocyte proliferation inhibiting factor, LPIF, or filtrate) can induce tolerance/hyporesponsiveness in vivo. We already knew from previous experiments that this material acted only on preactivated or malignant T cells, and even the malignant cells could be rescued from its action if cells were washed quickly after contact. To understand the mechanisms of its action, we have set up systems of specific stimulation. The material inhibits anti-Vbeta-specific stimulation. In a mixed lymphocyte reaction if responder cell populations from a first MLR performed in the presence of LPIF are harvested, extensively washed to discard suppressor molecules, and restimulated by related or third-party lymphocytes in an H2-incompatible combination, the response to a third-party stimulator (a primary one) is unaffected by prior exposure to the material, which nevertheless renders the population unresponsive to restimulation by the original MHC-stimulating haplotype. Cells triggered by anti-Vbeta6 antibodies in the presence of LPIF are unable to undergo restimulation by the very same anti-Vbeta6 MoAb, while they conserve their capacity to proliferate in a primary fashion in response to the unrelated anti-Vbeta8 MoAb. When analyzed by FACS using anti-Vbeta FITC-conjugated MoAbs, cells that are unresponsive or blocked in their proliferation by the action of the filtrate after anti-Vbeta stimulation are still live and unexpectedly transiently hyperexpress the TcR. These findings confirm the requirement for T cell stimulation for suppression to be enacted and demonstrate that such is exerted by anergy rather than by clonal deletion, at least in vitro.

The embryo expresses paternal antigens foreign to the mother and therefore has been viewed as an allograft. The maternal immune system responds to paternal antigens on the "graft", and these responses are thought to protect pregnancy. However, pregnancy can be aborted by stress, which stimulates local production of TNF-alpha and inhibits TGF-beta 2-producing natural suppressor cell (NS) activity via a neurotransmitter substance P-dependent pathway. Immunization protects against stress-triggered abortion and CD8+ T cells appear to be required. The objective of the present study was to investigate the importance of CD8+ T cells in the prevention of stress-triggered abortion by immunization. Injection of anti-CD8 increased the abortion rate in nonimmunized mice and in immunized mice. Following anti-CD8 injection, stress failed to further increase the abortion rate; a similar high rate of abortion was seen in immunized and anti-CD8-injected mice. These data suggested that stress could act by neutralization and/or elimination of immunoprotective CD8+ T cell function. CD8+ T cells from pregnant mice have been reported to produce a 34-kDa suppressor factor, but we detected a 1.5- to 2-kDa suppressive factor in the HPLC fractions of supernatants obtained from nonstressed decidua, and this activity was abolished by stress and boosted by immunization with Balb/c cells.

Partial resorption or abortion (depending upon the stage of gestation) can be induced with lower doses of lipopolysaccharide (LPS) (DIFCO) and human R-TNF than previously demonstrated. As can be expected, the abortion-prone CBA x DBA/2 and B10 x B10.A mating combinations are the most sensitive to such low doses. LPS synergizes with low doses of IL-2, gamma interferon, poly(I).poly(C) 12U. Treatment by GM-CSF, IL-3, or anti-natural killer antiserum decreases both TNF levels and abortion rates. Similar prevention of induced resorptions are obtained with either a neutralizing polyclonal rabbit anti-TNF antiserum or with pentoxyfilline, which has been shown to reduce resorption rates in CBA x DBA/2 pregnancies. More important, abortions induced by low doses of LPS or R-TNF can be prevented by alloimmunization. During late gestation, on the contrary, LPS- or TNF-induced delivery cannot be counteracted by alloimmunization nor by a progesterone-induced blocking factor, at least in the regimens employed by us. Therefore, although resorptions and parturition share common pathways consisting of immune mediators, they are not regulated similarly by the maternal immune system.

Spontaneous resorption (abortion) that occurs at a high rate in DBA/2-mated CBA/J female mice is dependent upon asialoGM1+ natural effector-type cells, can be ameliorated by alloimmunization or administration of GM-CSF, and is augmented by in vivo injection of anti-CD8 antibody. The abortion rate was similarly augmented by administration of monoclonal anti-GM-CSF neutralizing antibody, but the GM-CSF physiologically active in preventing abortion during normal pregnancy did not appear to be derived from maternal CB8+ T cells putatively responding to antigens on the fetoplacental unit. Rather, depletion of CD8+ cells in vivo prevented GM-CSF from reducing the rate of resorptions. GM-CSF administration rapidly downregulates natural effector cells able to kill a trophoblast target cell line in vitro, and anti-CD8+ antibody boosts total splenic cytotoxic cell activity. Further, anti-CD8 completely abrogated the ability of GM-CSF to suppress anti-trophoblast killer cell activity. These cells are known to be asialoGM1+ and injection of anti-asialoGM1 reduced the abortion rate appropriately in mice that had received anti-CD8. These data suggest that GM-CSF acts indirectly to prevent abortion in DBA/2-mated CBA/J mice through a mechanism that requires CD8+ maternal T cells, and systemic regulation of the level of anti-trophoblast killer cell activity may determine the success or failure of pregnancy in this system.

Graft versus host reaction (GVHR) and host versus graft reactivity during pregnancy share at least some cellular pathways. Immunosuppression mediated by placental suppressor factors may actively contribute to the survival of the conceptus in the immunocompetent mother. We have previously reported that supernatants from human choriocarcinoma cell lines inhibit mitogen-activated and antigen-activated proliferation of lymphoid cells. From this perspective, we investigated the capacity of supernatants from human choriocarcinoma cell lines (HCS) to suppress in vivo graft versus host reactions in mice. HCS was tested for its ability to block both local as well as systemic GVHR induced by the injection of parental cells into F1 mice. HCS mediates profound suppression of acute and chronic GVHR. These results confirm that human choriocarcinoma cell lines secrete a potent immunosuppressive factor(s) which can efficiently modulate immune responses in vivo.

The purpose of the present work was to establish whether the placenta is producing factors favoring an increased synthesis of asymmetric IgG antibodies which are known to assume a protective effect upon paternal antigens to which they largely are specific. In this way they can contribute to fetal survival in the maternal uterine environment. The hybridoma cell lines OKT8 (anti-CD8) and 112B4 (anti-DNP) were used in this respect since they synthesized both symmetric and asymmetric molecules of the IgG2a and IgG1 subclasses, respectively, murine isotypes in which anti-paternal antibodies have been detected. The cells were cultured in RPMI 1640 medium supplemented with 10% BCS and different amounts (5, 10, and 20%) of human placental supernatant. After incubation for 3 days at 37 degrees C in a humid chamber containing 5% CO2 the cells were centrifuged and the antibodies were obtained from the culture medium by a purification procedure involving precipitation at 50% ammonium sulfate saturation followed by DEAE-cellulose chromatography. Symmetric and asymmetric antibodies were separated by Con A-Sepharose affinity chromatography, the latter lectin retaining selectively only asymmetric IgG molecules. Both OKT8 and 112B4 hybridomas presenting a stable background synthesis of 15-17% of asymmetric antibodies have shown an increased level reaching 27-28% of these molecules in the presence of 5-10% placental supernatant added to the RPMI 1640 culture medium. These results clearly show that placental factors can up-regulate efficiently the synthesis of asymmetric IgG molecules of different isotypes secreted by plasma cells.

Local immunosuppression mediated by placental suppressor factors may contribute to the absence of consistently demonstrable cellular immunity against the fetus. In this context, we have investigated the immunosuppressive capabilities of supernatants from human trophoblastic choriocarcinoma cell lines (HCS) by testing the effects of HCS on immune responses in vitro and in vivo in the human and murine systems. HCS suppresses mitogen-induced proliferation and mixed lymphocyte reactions in humans and in mice, as well as antigen-induced T cell proliferation in mice. HCS also suppresses the in vivo response of mice to allogeneic cells. Furthermore, HCS when injected intraperitoneally causes the induction of suppressor cells in mice which in turn prevent the mounting of an allogeneic response in other strains of mice. These results indicate that human choriocarcinoma cell lines secrete a suppressor factor(s) which induces suppression in vitro as well as in vivo through the generation of suppressor cells.

We studied the in vivo antibody responses of three H-2b strains, BALB/b, C57BL/6 and BALB/B x C57BL/6 F1 to various lysozymes, REL and HEL, after priming with HEL, REL or the HEL N-terminal peptide. It was confirmed that C57BL/6 is a non-responder strain to HEL and that BALB/b is responder strain. The C57BL/6 non-responder trait was associated with HEL or peptide induction of suppressor cells, as shown by adoptive transfer experiments. We further demonstrated that the suppressor/non-responder trait is dominant in BALB/b x C57BL/6 F1 hybrids and that appropriately pulsed macrophages of BALB/b mice can bypass such suppression in these F1 mice. Possible mechanisms are discussed.

Earlier we showed that because of the presence of functional progesterone receptors, lymphocytes of healthy pregnant women produced an immunomodulatory protein in the presence of progesterone, whereas those of nonpregnant persons did not. Progesterone-treated murine pregnancy lymphocytes release a similar factor. The present study reveals the biologic significance of this finding. Treatment of BALB/c mice that were 8 days pregnant with a progesterone receptor blocker (RU 486) resulted in 100% resorption of the fetuses. Simultaneous administration of the supernatant from progesterone-treated murine pregnancy spleen cells restored the resorption rate to the original 6% observed in untreated control animals. These data suggest that functional lymphocytic progesterone binding sites are needed for the maintenance of normal pregnancy. Because of the blockage of progesterone receptors and the consequent inability of the lymphocytes to produce the progesterone-induced blocking factor, abortion is initiated by immune factors. The fact that administration of the preformed blocking factor counteracted the effect of antiprogesterone treatment suggests that progesterone-mediated immunosuppression is needed for the maintenance of normal gestation.

During pregnancy, maternal immune recognition of paternal alloantigens has been shown to result in an increased influx of maternal T cells into the spleen, draining lymph nodes and decidua. In previous studies we have shown that polyclonal or monoclonal anti-T cell antibody treatment of allogeneically pregnant mice results in decreased placental proliferation and phagocytosis in vivo. In the present study we compare the effect of such antibody treatment during allogeneic and syngeneic pregnancy. We show that monoclonal anti-CD8 treatment of both types of pregnant females reduces placental proliferation and phagocytosis. Anti-CD4 antibody treatment, on the other hand, only affects placental proliferation, indicating that there is a complex network of immune interactions affecting placental growth and function.

In this study we present evidence for reactivity of pregnancy lymphocytes, but not nonpregnancy lymphocytes, with the progesterone receptor-specific monoclonal antibody mPRI. Using an avidin-biotin peroxidase detection system, we found a nuclear staining in 14.6 +/- 3.7% (mean +/- SEM, N = 27) of pregnancy lymphocytes, while only 0.47 +/- 0.33% (mean +/- SEM, N = 15) of nonpregnancy lymphocytes reacted with the antibody. To characterize the receptor-bearing subset, CD8+ and CD4+ cells were depleted by complement-dependent lysis. Depletion of CD8+ cells was accompanied by 62 +/- 18% loss of progesterone receptor-bearing cells, while depletion of CD4+ cells resulted in a twofold increase in the number of positively staining lymphocytes. In nonpregnancy lymphocytes a 3-day PHA treatment, as well as allogeneic stimulation, resulted in a significant increase in the number of receptor-containing cells. These results suggest that pregnancy, but not nonpregnancy, lymphocytes contain progesterone binding structures, and that these are inducible by mitogenic or alloantigenic stimuli.

The effect of supernatants of concanavalin A-activated spleen cells (CAS) on the expression of various antigens, especially Ia antigens, on BALB/c B lymphoid cells, was examined. This study demonstrates the following: (i) CAS enhanced the expression of Ia antigens on four out of five BALB/c lymphoid cell lines. (ii) CAS selectively modulates the expression of Ia and H-2D, but not sIgM or viral gp70 expression, on X16C 8.5 tumor cells. The enhanced levels of Ia expression on B lymphoid tumor cells were also detected by using anti-Ia monoclonal antibodies. (iii) The molecular weight of soluble factor(s) affecting Ia and H-2 was approximately 40,000 estimated by gel filtration on a Sephadex G-200 column. (iv) Type 1 interferon but not interleukin 1, interleukin 2, or T-cell-replacing factor enhanced the expressions of Ia and H-2D antigens. (v) The activity of CAS-modulating Ia and H-2 antigens was eliminated by acidic treatment. It was concluded from this study that at least one of the factor(s) in CAS, modulating the antigenic expression of B-lymphoid cells, was interferon-like in nature. From our findings, a possible immunoregulatory mechanism by interferon was suggested: T cells, after stimulation of mitogens or antigens, secrete interferons which modulate the expression of Ia and H-2 on B cells. Then B cells, whose Ia and H-2 were modulated selectively by T-soluble factors(s), might interact with T cells much more efficiently.

Supernatants were prepared from short-duration explant cultures of term human placentas obtained after cesarean delivery. These supernatants inhibited murine and human mixed lymphocyte reactions, as well as CTL generation. The effects were reversed by an excess of IL-2-containing medium. Similarly, the material inhibited human natural killer cytotoxicity against K 562 targets. The material was subjected to gel-filtration chromatography on an ACA 44 or Bio-Gel A15m column. The apparent MW of the MLR-CML material was about 60-70 kDa, whereas the NK inhibiting activity was eluted in high-MW components (greater than 200 kDa) as well as in the 50-kDa range. The relevance of this material in local immunoregulation during human pregnancy is discussed.

CBA/J females (H-2k) mated with DBA2/J males (H-2d) exhibit a high rate of fetal resorption. Fetal survival has been improved by pretreatment of CBA/J females with spleen cells from BALB/c J (H-2d) (but not from CBA/J or DBA/2/J) males. Similarly, three out of nine recombinant inbred strains (recombining BALB/c and DBA2 genomes at the homozygous state) possess antiabortive effects like the BALB/c parent. Previous studies showed that BALB/c pretreatment triggers the appearance of suppressor cells in the spleen and of IgG1 anti-H-2d antibodies in the serum of CBA/J females. Studies of these two immunological parameters after CBA/J preimmunization by the different recombinant strains suggest that local intrauterine immunoregulation is the determinant of success or failure of allopregnancy.

Immunoregulatory cells in the maternal uterine endometrium and decidua are thought to play an important role in ensuring the success of the semiallogeneic conceptus. Two phases of suppression have been described in pregnant mice. Prior to implantation, the hormonal changes triggered by mating activate or recruit a population of nonspecific Lyt 2+ suppressor cells that inhibit cytotoxic T lymphocyte generation: this suppression appears to wane at the time or implantation and 4-5 days after implantation, a non-T suppressor cell population activated or recruited by fetal trophoblast cells develops. In this paper we confirm the non-major histocompatibility complex specificity of the hormone-regulated preimplantation suppressor cell. We show that this activity persists in the uterus during the early postimplantation period where its suppressive activity is masked by an Fc-receptor-positive cell population recruited by the implanting embryo. The potential importance of the persisting suppressor cells is suggested by an increase in the rate of spontaneous abortion of DBA2-mated CBA/J mice following injection of monoclonal anti-Lyt 2+ antibody in the early postimplantation period.

Maternal antibodies can be detected by immunofluorescence techniques on mouse placenta. Following acid elution, it is possible to characterize them as mostly IgG, mainly IgG1. It can be shown that they specifically bind paternal thymocytes and promote allogeneic mast cell degranulation, mainly specifically, but also to a lesser extent non specifically. The prolongation of survival of paternal strain tumor injected into a maternal strain animal demonstrate their enhancing activity.

Direct suppression of cytolytic effector cell function by cells of the placenta may represent one mechanism that protects the "fetal allograft" from rejection by maternal transplantation immunity. Collagenase disaggregated murine placental cells block target cell lysis by natural killer, lymphokine-activated killer, and (CTL)-type killer cells. This inhibition is reversible and noncompetitive, similar to a previously described inhibitor of CTL found in spleens of mice undergoing an acute graft vs host (GVH) response. Velocity sedimentation separation of placental cells shows that the inhibitory activity is primarily associated with cells that cosediment with nucleated fetal erythrocytes. When these erythrocytes were lysed, an increased number of non-erythrocytic cells could be separated and under this circumstance, inhibitory activity was seen in association with either small white cells or fetal erythrocytes and with large white cells. There may be several cell populations in murine placenta that can inhibit cytolytic effector cells. The possible relevance of direct placental inhibition of cytolytic effectors to protection of the "fetal allograft" is discussed.

Progesterone-treated pregnancy lymphocytes release an immunologic blocking factor. The mode of action of this substance was investigated. The supernatant of progesterone-treated pregnancy lymphocytes was highly suppressive of natural cytotoxicity toward human embryonic fibroblast target cells as well as of natural killer cell activity. The effect was not observed when progesterone induction was performed in the presence of RU 486, a progesterone receptor blocking agent. The factor was able to inhibit mixed lymphocyte reactions (MLRs), and transfer coculture experiments revealed that this effect was dependent on major histocompatibility complex nonspecific, nonrestricted suppressor T cells. The activation/expansion of suppressor inducer and suppressor effector T cells was further proved by fluorescence-activated cell sorter analysis of the populations from MLRs cultured in the presence of the inhibitory factor. These changes were not observed with MLRs performed in the presence of supernatants from progesterone + RU 486-treated peripheral blood lymphocytes. The inhibitory material, on the other hand, did not affect either production or function of IL-2. We conclude that in the presence of high local concentrations of progesterone, a suppressive pathway dependent on specific progesterone-CD8+ lymphocyte interaction might be established. This mechanism might play an important role in the maintenance of pregnancy.