Materno-fetal relations

Effect of pregnancy and placental factors on the quality of humoral immune response

Asymmetrical IgG molecules are characterised by the presence of a mannose-rich oligosaccharide group in only one of the two Fab fragments, which impairs the corresponding paratope, causing such molecules to behave as univalent antibodies and therefore as antigen blockers [1-3]. During human and murine pregnancy, an increase has been detected in asymmetrical IgG molecules in serum and those bound to the placenta, which normally releases factors capable of modulating the immune response. It thus seemed of interest to investigate the effect of placental culture supernatants (PCS) on in vivo and in vitro synthesis of rat immunoglobulin IgG1, IgG2a, IgG2b and IgG2C, particularly the ratio of symmetrical and asymmetrical molecules in each isotype. The effect of PCS was determined in vivo by means of passive transfer to virgin females and in vitro by analysing the supernatants of spleen cells cultured in the presence of PCS. The results showed that neither pregnancy status nor PCS were capable of modifying serum levels of IgG2a, IgG2b or IgG2c, whereas the level of IgG1 was reduced. When PCS were added to the spleen cells cultures, an in vitro increase was observed in IgG2a, IgG2b and IgG2c production. The separation of symmetrical from asymmetrical IgG molecules was performed by affinity chromatography in Concanavalin A-Sepharose, as such lectin binds high mannose sugars present only in asymmetrical IgG molecules. It is shown that pregnancy and PCS induce an increase in IgG1 and IgG2 molecules asymmetrically glycosylated, capable of binding to ConA-Sepharose. Therefore, the placenta is capable of releasing factors which can regulate the relative proportion of asymmetrical IgG molecules and induce quantitative and qualitative modifications of the in vitro and in vivo produced antibodies.

Incidence of rat-soluble placental factors on IgE and IgG2a synthesis

PROBLEM

The in vivo effect of soluble factors present in placental culture supernatants (PCSs) on the synthesis of rat immunoglobulin E (IgE) and IgG2a isotypes was investigated.

METHOD OF STUDY

Batches of Wistar SPF rats immunized with a 10-microgram dose of ovalbumin and Al(OH)3 were used: group I, consisted of virgin rats; group II, virgin females injected simultaneously with PCSs; and group III, pregnant females. As controls, nonimmunized batches were included. Serum samples were collected at days 0 (basal) and 10 after antigen challenge, determining levels of total and specific antiovalbumin of both IgE and IgG2a by enzyme-linked immunoadsorbent assay (ELISA).

RESULTS

In vivo and at least at the doses administered, PCSs exert an inhibitory effect on the synthesis of specific and total anti-ovalbumin IgE during the course of immune response to such challenge. However, PCSs did not modify serum values of total and specific IgG2a.

CONCLUSIONS

These results suggest that PCSs exert selective influence on the synthesis of diverse immunoglobulin isotypes during immune response, through the balance of cytokines synthesized by placental cells.

Murine fetal liver augments proliferation in an allogenic mixed lymphocyte culture: benzo(a)pyrene reduces augmentation

The effect of cells from the liver of C3H fetuses syngeneic to splenic responder cells on an allogeneic mixed lymphocyte response (MLR) was studied. After fractionation on ficoll-hypaque, interface cells from corn oil (vehicle for BP) or normal fetal liver (FL) controls (CO), obtained from 17-19 days gestation, enhanced proliferation in the mixed lymphocyte culture (> 2-fold), while cells from FLs transplacentally exposed to benzo(a)pyrene (BP) showed a decreased capacity for augmentation (> 2-fold less than CO). Unfractionated CO-FL cells at 0.5 x 10(6) did not augment proliferation, but at 0.25 x 10(6) enhancement with control FL cells was significantly higher than with BP-FL cells. Pelleted cells from BP- and CO-FLs were severely suppressive at the higher dose, while at 0.25 x 10(6) proliferation was augmented with CO-FL cells, but not affected with BP-FL cells. At doses of 0.1 x 10(6) or less, no effect was observed for either control or BP-FL cells. These data indicate that: a) FL cells syngeneic to responder cells of an allogenic mixed lymphocyte culture (MLC) have an augmenting but not suppressive capacity on cell proliferation; b) in utero insult with BP modifies the capacity of FL cells to augment proliferation in the MLC.

Inhibition of DNA synthesis and IL-2 bioactivity in MLR by splenic pregnancy-associated natural suppressor cells involves the production of a TGF-beta 1-like molecule and a second distinct inhibitory factor

Natural suppressor cells exhibiting a double-negative, immature T cell phenotype have been identified in maternal spleen during syngeneic murine pregnancy. In the present study, splenic pregnancy-associated natural suppressor (SPANS) cells are shown to express alpha/beta T cell receptors. SPANS cell-mediated inhibition of DNA synthesis by spleen cells responding in mixed lymphocyte reactions (MLR) is associated with a reduction in interleukin (IL)-2 bioactivity beginning after 96 h of culture. Although culture supernatants from suppressed MLR exhibit diminished ability to support the growth of IL-2-dependent CTLL-2 cells, SPANS cells themselves are unable to inhibit IL-2-driven CTLL-2 proliferation, suggesting that SPANS cells down-regulate IL-2 synthesis in MLR. IL-2 utilization in MLR is also inhibited by SPANS cells, since the addition of exogenous IL-2 fails to relieve the inhibitory effect of SPANS cells on lymphoproliferative responses in MLR. Flow cytofluorometric analysis reveals that MLR performed in the presence of SPANS cells contain normal percentages of CD4 and IL-2 receptor-bearing spleen cells. Thus, SPANS cells do not inhibit cellular proliferation in MLR by selectively interfering with clonal expansion of IL-2-producing helper T cells or by down-regulating IL-2 receptor expression. We have determined that SPANS cells inhibit DNA synthesis in MLR via the production of a transforming growth factor (TGF)-beta 1-like suppressor factor, since cellular proliferation in MLR is restored to normal levels in the presence of anti-TGF-beta 1 neutralizing antibody. However, IL-2 bioactivity in these cultures remains low in comparison to control MLR, suggesting the presence of a second distinct suppressor factor. Although the identity of this second inhibitory molecule has yet to be determined, neutralizing antibody studies have ruled out IL-10.

Immunotherapy of habitual abortion

Many cases of habitual abortion have been assumed to be due to hyporesponsiveness to the spouse's antigens encountered in pregnancy. Immunization by paternal leukocytes has been used to potentiate the immune response and prevent further miscarriages. This treatment has been highly controversial in terms of efficacy, mode of action, and side effects. More recently immunoglobulin has been used as passive immunization for similar indications. In our experience immunotherapy is effective; 80% of patients have subsequent live births. The most significant results are seen in patients with five or more abortions, in whom 66% of subsequent pregnancies develop normally compared to 20% in a control group. We have used antipaternal complement-dependent antibody (APCA) production after immunization as a marker of immune response. APCA correlates with beneficial outcome in the next pregnancy. APCA may also be associated with cytokines, which may enhance embryonic and trophoblast development. Immunoglobulin may similarly provide the relevant antibodies or cytokines. At present a large scale meta-analysis is being performed to confirm or refute the efficacy of this treatment. This meta-analysis may resolve the controversy.

Pregnancy-associated suppressor cells in mice: functional characteristics of CD3+4-8-45R+ T cells with natural suppressor activity

Natural suppressor (NS) cells are MHC-unrestricted regulatory cells with non-specific inhibitory activity for immune responses. In adult mice, NS cells are characteristically found in bone marrow and in splenic tissue following total lymphoid irradiation and cyclophosphamide treatments. Recently, we have shown that the spleens of pregnant mice harbour a population of lymphocytes which resemble NS cells in terms of phenotype and inhibitory activity. In this study, we use positive and negative selection techniques to further characterize splenic pregnancy-associated NS (SPANS) cells as predominantly 'double negative' T cells (CD3+4-8-) bearing receptors for the lectins wheat germ agglutinin and soybean agglutinin, as well as expressing CD45R and the heat-stable J11d.2 antigen. Taken together, these findings lead us to conclude that SPANS cells belong to an immature T cell lineage. In keeping with their T cell phenotype, SPANS cells do not express the natural killer (NK) cell-specific markers NK2.1 and asialoGM1 and do not mediate lytic activity against NK-sensitive YAC-1 cells, although natural cytotoxic activity against WEHI-164 cells was found to co-purify with SPANS cells. Suppressive activity of SPANS cells in mixed lymphocyte reactions (MLR) is abolished by treatment with mitomycin C, suggesting that natural suppression in this system is a proliferation-dependent phenomenon. Preincubation of SPANS cells with conditioned medium from Con A-stimulated T cell cultures results in augmented NS activity, indicating that SPANS cells respond to T cell signals. Our data suggest that SPANS cells mediate suppression via the elaboration of a soluble suppressor factor since SPANS cells do not require cell-cell contact to mediate suppression and supernatants from short-term cultures of SPANS cell-enriched SBA+ pregnancy spleen cells inhibit MLR. We believe that SPANS cell may be important in regulating hematopoiesis and maternal anti-fetal immunity during murine pregnancy.

Differential modulation of the in vitro lymphocyte activation pathways by soluble and solubilized placental substances

Soluble and detergent-solubilized placental extracts were studied for their modulatory effects upon the proliferation of lymphocytes stimulated by various activating agents. It was shown that soluble placental extract (SPE) exerted an inhibitory effect on the lymphoproliferation triggered by alloantigen or LPS but not by Con A or the combined action of PMA + calcium ionophore A 23187. This effect was also observed with SPE precipitated by 30% of ammonium sulfate (SPE30). On the other hand, a solubilized placental extract (SzPE) that was obtained by using octyl-beta-D-glucopyranoside inhibited the stimulation triggered by alloantigen, LPS, and Con A but did not affect the protein kinase C pathway. The modulatory effects were observed not only when SPE (or SPE30) and SzPE were added at the time of culture initiation but also at 24 h before or after the activating agents. Preincubation with SPE30 or SzPE immobilized on plastic surface, however, transduced an enhanced lymphoproliferative response to alloantigen and mitogen Con A but not to LPS. The above results suggest that placental substances exerted their modulatory effects by interfering mainly with the antigen or mitogen lymphoproliferation pathways.

Decidua-associated suppressor activity and viability of individual implantation sites of allopregnant C3H mice

Release of soluble suppressor activity from individual implant site decidua of DBA/2-mated C3H/HeJ mice was measured on days 12.5-13.5 of pregnancy. Suppressor activity varied among sites and followed a distribution curve that was displaced towards low suppression when resorption sites were compared to healthy embryonic implants. Pre-immunization against the DBA/2 strain paternal antigens failed to increase resorption (by loss of low suppression implants) but led instead to a reduced resorption rate. This was associated with an increase in soluble suppressor activity obtained from decidua. Some reduction in resorption occurred independent of an increase in the level of suppression suggesting additional contributing factors to the immunization effect.

Altered humoral immunoregulation during human pregnancy

The in vitro production of immunoglobulins in response to stimulation with pokeweed mitogen (PWM) and fixed/killed Staphylococcus aureus Cowan 1 (SAC) was measured in conjunction with in vivo assays of plasma immunoglobulin levels to examine the quality and quantity of humoral immunity during human pregnancy and at parturition. Following stimulation with PWM, there is a significant enhancement of in vitro immunoglobulin-G (IgG) production during pregnancy. Following stimulation with PWM and SAC, there was a significant reduction in in vitro immunoglobulin-M (IgM) production immediately following parturition. There was a significant decrease in the plasma levels of IgG during pregnancy, although no change in the plasma levels of IgM were observed. The decrease in plasma immunoglobulin levels during pregnancy cannot be explained as the result of hemodilution and transplacental transfer. Altered humoral immunoregulation is the most likely means whereby an increase in immunoglobulin production during human pregnancy could occur. The possible effects of this on the outcome of pregnancy are discussed.

Prostaglandin-E2 released by pre-implantation human conceptuses

This work investigates the production of prostaglandin E2 (PGE2), a well known modulator for the suppression of immune cells, by pre-implantation human conceptuses from the 4-cell stage to the hatched blastocyst and by cumulus oophorus cells, these being obtained from an IVF/ET program. Cumulus cell complexes cultured for 48 h produced considerable amounts of PGE2, necessitating complete removal of their influence on the conceptus cultures. All stages of the human conceptus studied produced PGE2 during 48-h cultures, the greatest amounts from late blastocysts, and from those cultured in media containing bovine serum albumin rather than human donor serum. Indomethacin-treated control blastocysts confirmed the synthesis and release from the human conceptuses. The production of PGF2a from human blastocysts could not be demonstrated.

Altered immune response patterns in murine syngeneic pregnancy: presence of natural null suppressor cells in maternal spleen identifiable by monoclonal antibodies

Expression of certain autologous lymphocyte-activating antigenic determinants on the developing embryo is known to provide a stimulus for maternal anti-fetal autoproliferative responses. If left unregulated these responses could exert negative influences on the reproductive process by converting to autoaggressive forms of immune reactivity. In normal circumstances, immunological reactions of this nature are therefore likely to be under the control of pregnancy-associated immunoregulatory elements found within the maternal/fetal environment. In the present investigation we describe a naturally occurring splenic inhibitory cell type devoid of conventional T, B, and macrophage surface markers associated with syngeneic murine pregnancy that is capable of exerting potent immunosuppressive effects on an in vitro expression of fetal/newborn T cell autoreactivity, namely the autologous mixed lymphocyte reaction (AMLR). Maternal spleen cells inhibitory for AMLR were found to be highly resistant to cytotoxic pretreatment with a panel of conventional antisera directed against T cell-specific antigenic determinants. The non-T nature of the natural splenic suppressor cell was further indicated by experiments showing that purified spleen T cells had no inhibitory activity. Pregnancy spleen cell populations that were effectively depleted of macrophages retained full ability to inhibit AMLR. Maternal suppressor activity could be localized to the spleen cell population bearing receptors for the B cell-specific lectin, soybean agglutinin (SBA). A panel of monoclonal antibodies prepared against enriched populations of suppressor cells was screened and selected for specific reactivity using an ELISA against glutaraldehyde-fixed SBA+ spleen cell subpopulations from pregnant versus virgin animals. Several of the monoclonals developed against suppressor-enriched spleen cell populations from isopregnant as well as allopregnant animals were effective in reducing or eliminating suppressor cell activity following cytotoxic pretreatment in the presence of complement. The novel set of anti-suppressor monoclonal antibodies described here should prove useful in furthering the isolation and characterization of pregnancy-associated suppressor cells and in determining their relationship to natural suppressor cell populations described in other systems.

Enhancement of murine splenic immunoglobulin secretion in vitro by supernatants from fetal and placental cell cultures

Supernatants from short-term cell cultures of fetal and placental tissues of mid-term allogeneically (CBA/Ca x C57/Bl) and syngeneically (CBA/Ca x CBA/Ca) pregnant mice were tested for B-cell enhancing activity in vitro. Immunoglobulin (Ig) secreting cells were detected by the protein-A-plaque assay and DNA synthesis was measured by the incorporation of [3H]thymidine. Supernatants from placental and fetal liver cell cultures (but not fetal fibroblasts) were significantly stimulatory to spontaneous IgM (and to some extent IgG) production in a system using adult untreated spleen cells as target cells. Conditioned media were also added to LPS- and PHA-activated spleen cell cultures. In this system none of the supernatants affected the development of Ig secretors. The DNA synthesis of the target cells was slightly depressed by the addition of conditioned medium from fetal and placental cells. The results indicate that the typical increase in the number of maternal splenic Ig secretors observed in vivo during murine pregnancy could be the result of enhancing factors deriving from the placenta and the fetus (e.g. fetal liver).

An investigation of allogeneic pregnancy in multiparous mice subjected to in vivo depletion of CD8 (Ly2)-positive lymphocytes by monoclonal antibody treatment

Adult thymectomized C57/Bl (H-2b) and DBA/1 (H-2q) female mice were subjected to treatment with rat anti-mouse CD8 and mouse anti-rat Ig (kappa) prior to entering their third pregnancy with CBA/Ca (H-2k) males. The treatment protocol drastically reduced the number of CD8 (Ly2)-carrying lymphocytes (T-cytotoxic/suppressor phenotype) in the spleen and para-aortic lymph nodes, as assessed by immuno-staining. All mice were investigated on day 18 of their third gestation. The following data were collected from experimental and control groups: (1) resorption frequency, (2) weight of the placenta, fetuses, spleen and para-aortic lymph nodes, (3) immunohistochemical analysis of maternal lymphoid tissues, (4) level of anti-paternal IgG serum antibodies, (5) content of "background" IgM and IgG-secreting cells in spleen and para-aortic lymph nodes. Neither the resorption frequency nor placental/fetal weight was affected by anti-CD8 treatment. However, the formation of anti-paternal antibodies was enhanced in anti-CD8 treated C57/Bl mice.

Maintained allogeneic pregnancy in rats depleted of T cytotoxic/suppressor cells by OX8 monoclonal antibody treatment

It has been suggested that CD8 positive suppressor T-cells might be of importance in the non-rejection of the fetus. In the present investigation allogeneically pregnant (Lewix x DA) rats were subjected to in vivo treatment with monoclonal OX8 antibodies, reactive with the rat equivalent of CD8 receptor. This treatment protocol drastically reduced the numbers of OX8 positive cells in spleens and para-aortic lymph nodes. On the day of delivery these rats, together with normal IgG treated controls, were dissected and analysed for effects on: (1) fetal survival; (2) weight and immunohistology of spleens and para-aortic lymph nodes; (3) total numbers of IgM- and IgG-secreting cells within these organs. The OX8 treated rats passed through pregnancy as successfully as did the controls. Both groups showed the same type of pregnancy-induced changes in their lymphoid organs, including dramatic growth of the para-aortic lymph nodes and increase in Ig-secretors within both spleen and para-aortic lymph nodes. This pattern was the same in all pregnant rats investigated, including untreated syngeneically mated Lewis rats. It is concluded that OX8 positive T "suppressor" cells do not play an important role in the maintenance of the fetal-placental unit.

Immunological and para-immunological mechanisms in spontaneous abortion: recent insights and future directions

Unexplained spontaneous abortion in humans is currently thought to be related to genetic or immunologic factors. Animal models of spontaneous abortion have been used to try to gain some insight into the problems in humans. From studies of animal models there is increasing evidence that a variety of mechanisms may initiate pregnancy failure and participation of immunologic effectors may be a secondary event. Recent studies indicate that murine abortion that occurs spontaneously (without deliberate immunization by the investigator) may be initiated by para-immunologic host effector cells such as NK cells, macrophages and their toxins that possess selective toxicity which is not antigen-specific. The potential importance of local non-specific suppressive mechanisms in the uterus is also highlighted by their ability to block non-specific para-immune effector cell activation, and by their potential relationship to growth factors in decidual supernatants that promote placental cell growth in vitro. Levels of non-specific suppression do not appear low when fetal death can be attributed to a genetic mutation. The concept that different tissue components of the feto-placental unit serve as targets of different immunologic and para-immunologic effectors is defined. The new insights into the pathophysiology of murine abortion and its correction can provide a useful framework for further analysis of the role of para-immunologic effector mechanisms in unexplained abortion in humans and in non-murine veterinary conditions.

Leucocyte populations in ectopic tubal pregnancy

Leucocytes at the ectopic implantation site in 10 cases of early tubal pregnancy were characterised with a series of monoclonal antibodies using an indirect immunoperoxidase technique on cryostat sections. Most were HLA-DR positive macrophages, and there were a small number of mature T lymphocytes (UCHT1 and Dako-T1 positive cells). These results were compared with those reported in normal first trimester intrauterine pregnancies, and the contributions of the various leucocyte types to successful implantation at both the ectopic and intrauterine sites were assessed.

Placenta accreta: an immunohistological study of trophoblast populations

Trophoblast populations in four cases of placenta accreta were characterized using antibodies directed against cell membrane antigens, placental hormonal products and low-molecular-weight cytokeratins in standard immunoperoxidase techniques. The results obtained with antibody to syncytiotrophoblast membrane (rabbit anti-StMPM), antibody to an epithelial membrane antigen (HMFGI) and a cytokeratin marker (CAM 5.2) appeared identical to those reported for normal term placental tissues. Similarly the localization of human placental lactogen (hPL), human chorionic gonadotrophin (hCG) and pregnancy-specific beta 1-glycoprotein (SP1) within trophoblast populations in placenta accreta was identical to their reported distribution in term placenta. However, increased reactivity at the villous-maternal junction was demonstrated with NDOGI, an antibody raised against term syncytiotrophoblast membrane and directed against hyaluronic acid. NDOGI reactivity at this site is normally maximal during early placental development and is virtually absent in the third trimester. The results suggest that placenta accreta does not arise through excessive trophoblast invasiveness or proliferation and the absence of decidua is of more importance in the pathogenesis. Trophoblast may regulate its development at an unfavourable intramyometrial implantation site by the production of hyaluronic acid.

Characterization of hormone-dependent suppressor cells in the uterus of mated and pseudopregnant mice

The survival of the implanted "fetal allograft" has been attributed to the action of local decidua-associated suppressor cells. These suppressor cells are Fc-receptor positive small lymphocytic cells lacking T-cell markers which arise following implantation, are localized at the implantation site, and block the action of IL-2 that stimulates NK and T effector cells. Kinetic studies have demonstrated the occurrence of an earlier peak of suppressive activity occurring 2-3 days after mating prior to implantation. The cells associated with pre-implantation suppression differs significantly from post-implantation suppressor cells. Velocity sedimentation studies show that early suppression is associated with large cells sedimenting at a modal velocity of 6-7 mm/hr. Suppressive activity from cells of similar size is also present in the uterine lining of hormonally-treated, pseudopregnant mice. In addition, suppressor cells can be demonstrated in the non-pregnant uterus at the time of estrus. These observations suggest suppressor cell activity may be hormonally regulated. The suppressor cell(s) in pseudopregnant mice bears Lyt 2.1 and Thy 1.2 surface antigens and suppressor(s) present in the pregnant animals bears Lyt 2.1 and Lyt 1.1. Although the suppressor cell was large, it did not appear to be a macrophage because it was resistant to antibodies to Mac-1 and FcR cell surface markers but susceptible to anti-T cell reagents. Furthermore, suppression was not mediated by a soluble factor that has been associated with the small lymphocytic suppressor. Thus, the suppressor activity present in the pre-implantation uterine lining appears to differ significantly from the suppressor cell activity found after implantation. The possible role of a hormone-activated suppressor T cell in the success of the pregnancy is discussed.

Immunosuppressor factor(s) produced by decidua-associated suppressor cells: a proposed mechanism for fetal allograft survival

Mechanisms that explain failure of rejection of the antigenic fetus by the mother appear to lie at the fetomaternal interface. Successful pregnancies have been correlated with the presence of decidua-associated suppressor cells. Supernatants from these cells were tested for their ability to suppress the proliferation of interleukin 2-dependent cells and were also subjected to high-performance liquid chromatography. Decidual supernatant was found to have peak suppressive activity at two molecular weights (43,000 and 21,000 daltons). The activity of decidual supernatant was directed specifically at interleukin 2-dependent cells and interfered with interleukin 2 action. The importance of this mechanism in graft rejection is well known. Decidual supernatant may thus prevent fetal allograft rejection by preventing the maternal cytotoxic effectors from receiving the interleukin 2-dependent help that they need to proliferate and remain actively cytolytic.

Characterization of the cellular basis for the inhibition of cytolytic effector cells by murine placenta

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.

The rat placenta expresses paternal class I major histocompatibility antigens

The expression of paternally inherited class I MHC antigens on the placental trophoblast of the rat has been investigated using a mouse anti-rat monoclonal antibody (MN4-91-6) in an indirect immunoperoxidase labelling assay on cryostat sections. Strong specific staining was obtained on the spongy zone trophoblast of the mature placenta from DA male (RT1a) X PVG female (RT1c) matings. In marked contrast, no staining was observed on the labyrinthine trophoblast nor on the trophoblastic giant cells at any stage of gestation from 8 to 19 days post-coitum. None of the trophoblastic cell populations at any stage of gestation were reactive with an anti-class II monoclonal antibody. Class I positive endovascular cytotrophoblast cells were present in the maternal arterial sinusoids of the decidua. These findings imply that maternal immunoregulatory mechanisms must be essential for the survival of the placenta and fetus.

Preliminary characterization of two types of suppressor cells in the human uterus

Survival of the mammalian fetus in an immunologically hostile host has been shown to be determined by the properties of the tissue at the maternal-fetal interface. Suppressor cells have been found in the decidua in both murine and human systems. This study was carried out to further characterize these cells and to determine whether they were present in abnormal early pregnancies and in the endometrium at the time of implantation. Suppressor cells appear in the endometrium after ovulation, and their activity is present in the decidua of successful pregnancies but is absent in missed abortions. Two types of cells have been identified. An early phase large cell appears to be hormone dependent, and later phase small cell appears to be trophoblast dependent. This would suggest that suppressor cells may play a role in protecting the fetal allograft, from the time of implantation, against maternal immunity, thereby allowing a pregnancy to succeed.