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

Selective abortion and the evolution of genomic imprinting

Mothers can determine which genotypes of offspring they will produce through selective abortion or selective implantation. This process can, at some loci, favour matching between maternal and offspring genotype whereas at other loci mismatching may be favoured (e.g. MHC, HLA). Genomic imprinting generally renders gene expression monoallelic and could thus be adaptive at loci where matching or mismatching is beneficial. This hypothesis, however, remains unexplored despite evidence that loci known to play a role in genetic compatibility may be imprinted. We develop a simple model demonstrating that, when matching is beneficial, imprinting with maternal expression is adaptive because the incompatible paternal allele is not detected, protecting offspring from selective abortion. Conversely, when mismatching is beneficial, imprinting with paternal expression is adaptive because the maternal genotype is more able to identify the presence of a foreign allele in offspring. Thus, imprinting may act as a genomic 'cloaking device' during critical periods in development when selective abortion is possible.

Relationship between MLR blocking antibodies and the outcome of the third pregnancy in patients with two consecutive spontaneous abortions

To determine the relationship between mixed lymphocyte culture reaction (MLR) blocking antibodies (BAbs), immunological humoral factors, which generated in pregnant women and the outcome of pregnancy, the natural outcome of the third pregnancy in fifty-five patients with primary twice consecutive abortion was evaluated, and MLR-BAbs in sera were examined during their third pregnancy. The third pregnancy in 39 of 55 patients (70.9%) continued successfully, and remaining 16 patients (29.1%) experienced repeated abortion at the first trimester. Out of these 55 patients, MLR-BAbs were examined in 27 (17 with successful outcome and 10 with repeated abortion). The positive rate of MLR-BAbs was 82.4% in patients with successful outcome (15 of 17 cases), and that in patients with repeated abortion was 10% (one of 10 cases). The positive rate of MLR-BAbs was significantly higher in the successful pregnancy group compared with that in the repeated abortion group (p < 0.001). The blocking effect on MLR significantly increased along with the prenatal course in patients with successful outcome. Thus, MLR-BAbs are strongly associated with the outcome of pregnancy in patients with primary twice consecutive spontaneous abortions.

Rat GST 8-8 is expressed predominantly in myeloid origin cells infiltrating the gravid uterus

Previous studies from our laboratory have shown a relatively high expression of rGST8-8 in uterine tissues. This GST isozyme displays relatively high glutathione-peroxidase activity towards lipid-hydroperoxides and towards toxic 4-hydroxyalkenals generated from lipid peroxidation. Since the uterus is a unique organ, subject to oxidative stress due to infiltration by immune effector cells during gestation and because this infiltration is readily identifiable histologically, the studies reported herein were performed to localize the cell specific expression of rGST8-8 to determine whether immune effector cells infiltrating the pregnant rat uterus specifically expressed rGST8-8. A 75 bp end-radiolabeled cRNA probe was prepared from the full length mGSTA4-4 cDNA from the region which is highly homologous with rGST8-8. This cRNA probe was used for in situ hybridization studies to localize rGST8-8 in specific cell types of gravid rat uterus. Results of these studies indicate that this GST isozyme is selectively expressed in myeloid origin cells such as monocytes/macrophages, and neutrophils infiltrating the uterine endometrium and in vascular walls. Selective expression of rGST8-8 in the myeloid origin cells, which are known to generate higher levels of reactive oxygen species, suggests that this GST isozyme plays an important role in the protection mechanisms against lipid peroxidation.

Immunologically mediated abortion (IMA)

Roughly 20% of all clinical pregnancies evolve into "spontaneous abortions". The causes of spontaneous abortion have been determined in under 60% of the total and comprise genetic, infectious, hormonal and immunological factors. In some cases the immune tolerance mechanism may be impaired and the foetus immunologically rejected (IMA, immunologically mediated abortion). The immunological mechanism implicated depends on the time in which pregnancy loss takes place. During preimplantation and up to the end of implantation (13th day) the cell-mediated immune mechanism (potential alloimmune etiologies) is responsible for early abortion. This mechanism involves immunocompetent decidual cells (eGL, endometrial granulated lymphocytes) already present during pre-decidualization (late luteal phase) and their production of soluble factors or cytokines. Once the implantation process is over, after blastocyst penetration of the stroma and the decidual reaction of uterine tissue, IMA could be caused by cell-mediated and humoral mechanism (anti-paternal cytotoxic antibodies or autoantibody etiology), by the production of paternal anti major histocompatibility complex antibodies, or even by an autoimmune disorder leading to the production of autoantibodies (antiphospholipid antibodies, antinuclear antibodies or polyclonal B cell activation). The diagnostic work-up adopted to select IMA patients is crucial and includes primary (karyotype of both partners, toxo-test, hysterosalpingography, endometrial biopsy, thyroid function tests, serum hprolactin, luteal phase dating) and secondary (full hemochromocytometric test, search for LE cells, lupus anticoagulant, anticardiolipin, antinuclear antibodies, Rheumatoid factor, blood complement VDRL) investigations. Therapeutical approaches vary. If autoimmune disorders are demonstrated therapies with different combinations of corticosteroids, aspirin and heparin or intravenous immunoglobulin are administered. Otherwise, therapy with paternal or donor peripheral blood mononuclear cells should be instituted.

Evaluation of the role of exogenous pathogens on the incidence of embryo loss during early pregnancy in mice

The mating of CBA/j female mice (H2k) by DBA/2j male mice (H2d) typically results in an elevated incidence of spontaneous embryo loss thus providing an ideal genetically controlled laboratory model for the study of the factors causing early embryo loss during pregnancy. There is now considerable data on the cells and factors involved in fetal resorption but little is known about the events which activate this process. While the activation of the maternal response to the fetal implant could have endogenous or genetic origins, a role for exogenous factors including microbial pathogens could also be involved. In order to investigate these possibilities, the reproductive success of CBA/j female x DBA/2j male matings in a conventional animal care facility were compared with matings in a specific pathogen free (SPF) animal facility. All animals housed under these conditions were routinely screened by immunoassay and culture, for the presence of a number of viral and bacterial pathogens of mice. The incidence of spontaneous embryo loss in specific pathogen free CBA female mice mated by DBA and other male strains was found to be virtually identical to that of CBA female mice infected with multiple viral pathogens and housed under otherwise identical conditions (non-SPF). However, the numbers of implantation per pregnancy was significantly greater in an SPF facility. Therefore, exposure of mating mice to exogenous viral and bacterial pathogens did not appear to alter the overall incidence of spontaneous embryo resorption. It was concluded that the immunomodulatory effects of infection by common murine pathogens neither augmented nor reduced post-implantation embryo losses.

Inhibitory effect of choriocarcinoma-derived high molecular weight factor (HMWF) on lymphocyte proliferation and adhesion to trophoblasts

Trophoblast-secreted soluble factors may deter the immune rejection of the fetus which can occur from interaction between maternal lymphocytes and fetal trophoblasts in decidua. The effect of size-fractionated culture fluid of choriocarcinoma cells on the function of lymphocytic cells was studied. The results show that dialyzed soluble factor (HMWF) of molecular weight > 100 kDa was inhibitory to lymphocyte proliferation in a dose-dependent manner and prevented lymphocyte-to-trophoblast adhesion in a similar fashion. The effect was abrogated by a freezing-thawing process and heat treatment. Similarly, the fractions below 100 kDa size had no effect on lymphocyte functions. Although the nature of HMWF is not yet known, it appears that this factor differs from most of the well-characterized pregnancy factors but is similar to the recently described high molecular weight factor found in primary cultures of trophoblasts and choriocarcinoma lines. The inhibitory effect of trophoblast-derived HMWF on cell-contact-based immune recognition may contribute to maternal tolerance.

Suppression of cytotoxic T-lymphocyte activity during human pregnancy

We have investigated alterations in Epstein-Barr virus antigen specific cytotoxic T-lymphocyte (EBV-CTL) activity during human pregnancy. EBV-CTL activity was determined by a modified EBV induced B-cell focus regression assay and was expressed in terms of a regression index (IR50), i.e. the initial cell concentration required to achieve a 50%-incidence of regression in EBV-infected cell culture. Increased values of IR50 indicate the suppression of EBV-CTL activity. In 113 human female T-cell leukemia type-I (HTLV-I) non-carriers, the IR50 values (mean +/- S.E.) in non-pregnant, pregnant (the first trimester, second trimester and third trimester of pregnancy) and puerperal women were 10.6 +/- 1.4, 16.1 +/- 1.1 (20.1 +/- 2.0, 14.8 +/- 2.0, 14.6 +/- 1.6), and 12.1 +/- 1.9 respectively. Among HTLV-I carriers, the IR50 values (mean +/- S.E.) were likewise 34.6 +/- 8.0, 87.4 +/- 5.2 (101.7 +/- 6.3, 88.3 +/- 8.4 and 79.5 +/- 9.2) and 39.2 +/- 7.1 respectively. This data demonstrate: 1) EBV-CTL activity was suppressed during pregnancy (P < 0.05), especially in the first trimester (P = 0.0003). 2). In HTLV-I carriers, this suppression was shown in the first trimester (P = 0.0002), in the second trimester (P = 0.0002) and in the third trimester of pregnancy (P = 0.0014) and 3). One month after delivery, this suppression had returned to the non-pregnant level in both HTLV-I non-carriers and HTLV-I carriers. Pregnancy therefore has a suppressive effect on antigen specific cytotoxic T-lymphocyte activity and this effect is amplified in HTLV-I carriers.

Quantitative and qualitative changes in the intraepithelial lymphocyte population in the uterus of nonpregnant and pregnant sheep

PROBLEM

Previous studies have revealed the presence of a unique population of CD45R+ granulated cells in the sheep uterine epithelium. In the present study, dramatic changes in this cell population and in the nongranulated lymphocytes in the uterine and endometrial glandular epithelium of non-cycling, cycling, pregnant, and postparturient sheep are described. In noncycling and cycling sheep, the granules in the granulated intraepithelial cells were small. From days 55 to 134 of pregnancy, the granules in these cells were large, and there was a significant increase (P < 0.01) in the proportion of this cell population in the uterine epithelium but not in the endometrial glandular epithelium located in the deeper region of the stroma. The number of these cells declined dramatically (P < 0.01) from 2 to 15 days after parturition. Both the tissue distribution and the time of activation of these cells suggests they are different from the granulated lymphocytes described in placentae of mice and man.

CONCLUSIONS

It is concluded that this unique population of granulated cells is derived from lymphocytes, and that these cells become metabolically active from mid- to late-pregnancy and may play a physiological role during pregnancy or birth. In contrast, the number of nongranulated intraepithelial lymphocytes were suppressed throughout pregnancy and they probably do not play a role in pregnancy.

Mouse model for the treatment of immune pregnancy loss

Spontaneous abortions can be associated with preimplantation embryo loss, implantation problems and a variety of postimplantation pregnancy failures. The long list of possible causes for the postimplantation pregnancy loss includes, among others, genetic abnormalities in fetus, anatomical abnormalities of the uterus, endocrinological insufficiency, and microbiological problems. However, more than 50% of recurrent miscarriages still have no recognized causes. The concept that many such abortions may be immunologically mediated has gained increasing support over the years. Moreover, immunization of such women with husband's or third party leukocytes has resulted in more than 70% of subsequent pregnancies resulting in live births. Since neither the mechanisms leading to pregnancy loss nor the success of immunotherapy are clear, the set-up of animal models for recurrent abortions would be of supreme significance. Our recent data show that immunopotentiation of maternal immune system by Complete Freund Adjuvant significantly improves pregnancy rate in CBA x DBA/2 mouse combination with high percentage of fetal resorptions. This effect is followed by decrease of IL 2 production in spleen; increase of MAC 1-positive cells at placenta; amplification of suppressive activity of local and systemic lymphocytes and by reverse of embryotoxic effect of maternal serum. Data obtained in this model seems to be valuable in substantiation of rationale for nonspecific immunotherapy of human abortions.

The effect of horse placental tissue extracts and equine chorionic gonadotrophin on the proliferation of horse lymphocytes stimulated in vitro

Commercial preparations of equine chorionic gonadotrophin (eCG) and extracts of horse placenta taken at 80 days gestation were incorporated into mixed lymphocyte culture and mitogen stimulation assays of horse peripheral blood mononuclear cells. A dose-related inhibition of lymphocyte proliferation, indicative of immunosuppressive activity, was observed in both systems, both with commercial eCG preparations and tissue extracts. Negligible inhibitory activity was observed with an extract of term placenta. The inhibitory activity of the placental samples was not related to their eCG content as measured by immunoassay. The fact that one pregnant horn allantochorion extract containing 50 IU/ml of eCG showed an identical dose-dependent lymphoproliferation-inhibitory activity to an extract of a second such allantochorion containing only 1.7 IU/ml of eCG suggests that this hormone does not inhibit lymphocyte proliferation and that commercially available eCG contains inhibitory contaminants.

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.

Lymphocyte-derived progesterone-induced blocking factor corrects resorption in a murine abortion system

An anti-abortive effect of a progesterone-induced blocking factor has been shown in the CBA/J x DBA/2 abortion system. I.p. injections of pregnant mice on days 7.5, 9.5, and 11.5 of gestation with dialyzed supernatants from progesterone-treated murine pregnancy spleen cells (but not from control ones) significantly (P less than 0.01) reduced the resorption rate from 47.7% in the untreated animals to 20.7%.

Suppression of interleukin-2 mediated T-lymphocyte blastogenesis by bovine uterine secretions

Uterine luminal protein (ULP) secretions collected on day 17 of bovine pregnancy contain high (greater than or equal to 248 kDa)- and low (7, 21.0, and greater than or equal to 72 kDa)-molecular weight (Mr) components that suppressed incorporation of thymidine into both phytohemagglutinin (PHA)-stimulated and interleukin-2 (IL-2)-stimulated bovine lymphocytes. The pattern of suppressor activity for ULP was similar for both PHA and IL-2 cultures. For IL-2-treated lymphocytes (2 X 10(4)/culture well), mean percentage of control (no test protein) values for 8 and 32 micrograms/ml of high Mr ULP were 94.6% and 4.5%, respectively; whereas, mean values for 8 and 64 micrograms/ml of combined low Mr ULP components were 51.2% and 5.5%, respectively. The data indicate that specific bovine ULP components may locally affect T-lymphocyte function by altering some facet of the IL-2 activation system.

Inhibition of natural killer cell activity by retroplacental sera as compared to peripheral sera. Lack of influence of immune complexes

A decrease of natural killer cell activity (NKCA) during human pregnancy might contribute to the acceptance of the allogeneic fetus by the maternal host. The inhibition of NKCA might be due to serum factors derived from the trophoblast. We focused especially on the role of immune complexes, as it has already been described that these complexes depress NKCA and as they are found frequently in retroplacental serum. We have compared the influence of 19 paired retroplacental and peripheral blood sera on NKCA of normal donors. One peripheral and eight retroplacental sera contained immune complexes. Normal donor mononuclear cells were incubated with carboxyfluorescein-labeled K562 cells in the presence of retroplacental serum or peripheral serum. NKCA was measured on a FACS Analyzer. Ten of 19 retroplacental sera inhibited NKCA significantly in comparison to the corresponding peripheral serum (P = 0.003). There was no correlation between NKCA and the immune complex level. We conclude that, as compared to peripheral serum taken at delivery, there is a retroplacental serum-induced inhibition of NKCA, which is not correlated with the presence of immune complexes.

Peripheral large granular lymphocytes in normal pregnant and postpartum women: decrease in late pregnancy and dynamic change in the puerperium

Large granular lymphocytes (LGLs) have a variety of cytotoxic activities of NK, K and cytotoxic T lymphocytes, suggesting that their morphology is indicative of lytic function. In non-pregnant normal control women (n = 48), the number of LGLs was 0.30 +/- 0.14 x 10(9)/l and the proportion of LGLs in their peripheral lymphocyte fraction was 14.0 +/- 5.4%. The number and proportion of LGLs were significantly decreased in the third trimester of pregnancy (n = 32; 0.19 +/- 0.08 x 10(9)/l, P less than 0.01, and 11.7 +/- 3.8%, P less than 0.05), although an unexpected increase in the proportion of LGLs was observed in the first trimester of pregnancy (n = 24; 17.5 +/- 6.5%, P less than 0.05). After delivery, the number and proportion of LGLs increased rapidly to restore the non-pregnant levels and showed a marked increase in LGL count 4 months postpartum. These data suggest that lymphocyte-mediated cytotoxicity decreases in late pregnancy and increase dynamically after delivery to restore the non-pregnant state.

Immunoactive products of human placenta. II. Direct inhibition of non-MHC restricted cytolytic activity of human CD3 alpha-beta but not CD3 gamma-delta expressing T cell clones

The effect of human placental supernatant obtained from explant cultures of caesarean delivery placentae was monitored on both alpha-beta human T cell clones, which display both cytotoxic alloreactivity and non-MHC restricted cytotoxicity against K562 target cells, and gamma-delta ones endowed solely with the latter. It was found that, under appropriate experimental conditions, direct inhibition of the cytolytic activity of alpha-beta T cell clones was exerted by the supernatant. In contrast, gamma-delta T cell clones were unaffected. The relevance of these data to the survival of the fetal allograft is discussed.

Hormone-induced preimplantation Lyt 2+ murine uterine suppressor cells persist after implantation and may reduce the spontaneous abortion rate in CBA/J mice

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.

The immune function of the endometrium

The endometrial mucosa is unique amongst mucosal sites in that it must mount an immune response against micro-organisms and resist tumour growth whilst tolerating sperm and the allogeneic fetus. Bacterial and viral infection in the uterus leads to local endometrial mucosal immune responses evidenced by the secretion of secretory component (SC), secretory IgA (sIgA) and IgG. The secretion of these molecules is under hormonal control. Trafficking of locally sensitized lymphocytes to other mucosae does not appear to occur, whereas priming at other mucosal surfaces leads to memory responses to antigen in the uterus. Proclivity to local immune function is related to sparse lymphatic supply to the endometrium together with a local distribution of antigen-presenting dendritic cells. During pregnancy, particularly in the region of the decidua and embryo, the number of Ia+ cells and the lymphatic supply become diminished. The antigenic status of sperm may lead to certain types of maternal sensitization. However, immunosuppressive factors in seminal plasma protect the sperm on its passage up the female genital tract and diminish subsequent immunogenicity. On fertilization of the oocyte, an allogenic fetus develops, that potentially could stimulate production of maternal immune effectors. Endometrial cells of various types (macrophage, decidual, NK, T cells) interact via soluble factors leading to a local immunoprotection of the fetus. Similar factors appear to operate in resisting tumour growth in the uterus.

Hemopoietic origin of certain decidual cell precursors in murine pregnancy

The possible hemopoietic origin of certain precursors of uterine decidual cells appearing during normal murine pregnancy was investigated in semiallogeneic hemopoietic chimeras with retained or regained fertility. Chimeras were produced by three different methods in two donor-host combinations: F1 [BALB/c female x C3H/HeJ male] cells introduced into the parental strain BALB/c female hosts or F1 [CBA/J female x C57BL/6 male] cells introduced into CBA/J female hosts. Prenatal chimeras (PN) were made by reconstituting mouse fetuses (day 13-17) with 10(6)-10(7) adult bone marrow or fetal liver cells through the yolk sac and they were allowed to be delivered naturally. Neonatal chimeras (NN) were made by injecting 1-2 x 10(7) adult bone marrow cells into the anterior facial vein of neonatal mice (less than 24 hr old). In both cases, experimental animals were raised to maturity. Ovary-transplanted chimeras (OT) were made by injecting 10(7) bone marrow cells into lethally irradiated (9.5 Gy) young adult female mice, followed 6 weeks later with bilateral orthotopic transplants of syngeneic ovary grafts to restore fertility. All female chimeras produced by the three different methods were mated with syngeneic male partners to produce normal pregnancy. The extent of chimerism at the cellular level was determined in all cases by a radioautographic identification of the H-2 phenotype of splenic lymphocytes and decidual cells and macrophages in the collagenase-dispersed decidua at day 11-16 of normal pregnancy, following a sandwich labelling with monospecific anti-H-2 antibodies and 125I-protein A. Morphological discrimination of typical decidual cells from macrophages in the collagenase-dispersed decidua was carried out on the basis of several distinctive markers: presence of surface Dec-1 and Thy-1 and absence of surface F4/80 or latex phagocytosis for decidual cells, in contrast to macrophages which were phagocytic and expressed F4/80 but not Dec-1 or Thy-1. While the degree of hemopoietic chimerism (judged by the incidence of donor-derived lymphocytes in the spleen) varied from animal to animal, in all three groups (PN, NN, and OT) comprising a total of 26 chimeras, the percentage of typical decidual cells expressing donor H-2 phenotype showed an excellent correlation with that for small lymphocytes in the spleen. These results reveal that at least a subpopulation of typical decidual cells of the pregnant uterus has a hemopoietic genealogy. A possible familial relationship of these cells to granulated metrial gland cells remains unclear.

Association between recurrent spontaneous abortions and circulating IgG antibodies to sperm tails in women

The isotype and regional specificity of antisperm antibodies in the circulation of women with recurrent spontaneous abortions was examined. There was a statistically significant association (P less than 0.005) between the presence of IgG tail-directed antisperm antibodies and a history of unexplained recurrent spontaneous abortion. These antibodies were detected in 36.4% of 44 women with recurrent abortions and 14.6% of 616 female partners of infertile marriages. In contrast, no differences in IgG sperm head-directed antibodies or in IgA and IgM antisperm antibodies were observed between the two groups. Husbands of women in the miscarriage or infertile groups had similar semen evaluations. Antisperm antibodies may be a marker for defective immunosuppression in women with recurrent miscarriages. Alternatively, exposure of sperm-sensitized pregnant women to sperm may activate the maternal immune system to respond to paternal antigens present on the embryo.

Peripheral K cells in normal human pregnancy: decrease during pregnancy and increase after delivery

Peripheral blood levels of K cells were measured in normal pregnant and post-partum women by a plaque-forming cell technique that detects K cells on the basis of their activity of antibody-dependent cell-mediated cytotoxicity (ADCC). Peripheral K cells decreased throughout normal pregnancy (n = 46; 7.8 +/- 3.4%, P less than 0.01; 0.13 +/- 0.08 X 10(9)/l, P less than 0.001) and increased in the post-partum period (n = 17; 14.2 +/- 6.1%, P less than 0.05; 0.32 +/- 0.20 X 10(9)/l, P less than 0.01) in comparison with those in normal non-pregnant controls (n = 29; 10.5 +/- 4.2%; 0.20 +/- 0.09 X 10(9)/l). These findings suggest that a decrease of K cells during pregnancy may contribute in part to maternal acceptance of the fetal allograft and that the post-partum increase of K cells may represent a post-partum increase of cell-mediated cytotoxicity, which may contribute to natural defense against puerperal infection.