Influence of the mother's preceding pregnancies on fetal development and postnatal survival of the neonate, in normal pregnancy. An immunological phenomenon?

OBJECTIVES

The objective of this study is to test for an association between the sex of conceptuses of the mother's preceding pregnancies and fetal development and early neonatal survival in normal pregnancy.

METHODS

A population of 27,243 neonates, including a subsample of 7,773 "newborn/mother/placenta units" were divided into cohorts according to the sex of the neonate and the sex and number of conceptuses of the mother's preceding pregnancies. The average birth weight, placenta weight and early neonatal mortality rate were measured for each cohort and compared. The "dose effect" of preceding pregnancy was tested by linear and quadratic regression analysis, and by chi-square trend test for linearity of proportions.

RESULTS

The results have shown an association between these three variables and the preceding pregnancies of the mother. Fetal development and early survival of the neonate are positively associated with the mother's preceding pregnancies of same sex as the neonate, and negatively associated with the preceding pregnancies of opposite sex to the neonate. The strength of the phenomenon increases with parity, at least for the first three parities. The association is statistically significant.

CONCLUSIONS

The association between fetal development and neonatal survival and preceding pregnancies of the mother would be compatible with the action of male and female specific antigens capable of affecting selective implantation of blastocysts, which commands subsequent fetal development as well as early neonatal survival.

Maternal immunological recognition mechanisms during pregnancy

One of the most intriguing shortcomings of modern immunology, especially transplantation immunology, is its failure to provide a satisfactory final explanation for the consistent non-rejection of immunogenetically alien conceptuses in utero, even in specifically preimmunized females. Certainly, there is no shortage of hypotheses. Over the past few years various observations have utterly refuted the simplistic notion that the much-mated but nulliparous or gravid females are immunologically unaware of the presence and activities of allogeneic cells transiently or chronically within their reproductive tracts. This evidence has engendered the belief that some kind(s) of active response(s) on the part of the female, following early recognitive events, plays an important, if not essential, role, in conjunction with adaptive hypoantigenicity of the trophoblast, not only in conferring selective benefits upon the conceptus from the time of implantation, but also in affording it protection from the possible hazards of a cellular immunity. Evidence is emerging that during mating, implantation, placentation, and gestation (1) various fetal and histocompabibility antigens are presented to the mother in a unique manner; (2) she does respond to these; and (3) her responses aid in the establishment and maintenance of a harmonious state of immunological coexistence with her fetus. There are reasonable grounds for believing that a complete understanding of the immunobiology of the maternal-fetal relationship may facilitate significant advances in both transplantation and tumour immunology.

Dominant negative suppression of major histocompatibility complex genes occurs in trophoblasts

BACKGROUND

Polymorphic class I and II major histo-: compatibility complex (MHC) genes are not transcribed in trophoblasts although many immune system cells express these genes constitutively. To study the molecular biology of MHC suppression for the purposes of potential transgenic animal development, we examined the effect on MHC expression in B cells by fusing them with trophoblasts.

METHODS

Trophoblasts and B cells with separate selection markers were fused with polyethylene glycol. After growth in double selection media, the hybrids were analyzed for HLA-A, -B, -C, -DR, -DP, and -DQ expression by fluorescence-activated cell scanning and class I and II mRNA by Northern blotting. Class II promoter activity in trophoblasts was then analyzed by transfection of a lethal reporter construct and subsequently, the class II transactivator.

RESULTS

Class I and II surface antigens and their corresponding mRNA were completely suppressed in the hybrids. The lethal reporter construct demonstrated that class II suppression resulted from lack of activation of the class II promoter. This in turn was caused by lack of functional class II transactivator.

CONCLUSIONS

These data indicate that dominant negative trophoblast factors, either directly or indirectly, suppress expression of the MHC genes. If these factors can be cloned, the potential exists for developing transgenic animals that cannot express MHC or peptide antigen to T cell receptors through the MHC system.

Human placental Fc gamma-binding proteins in the maternofetal transfer of IgG

Annexin II, a member of the annexin family of Ca2+ and phospholipid binding proteins, is present in human placenta. Placental annexin II has low affinity FcR activity, and is present as a heterotetramere on syncytiotrophoblast apical cell membrane extracellular surface. In addition to annexin II, transmembraneous leukocyte FcRIII is present on syncytiotrophoblast apical membrane. Either one, or both molecules may mediate the binding of IgG and thereby facilitate its transport through the syncytiotrophoblast layer. However, the presence of other maternal plasma proteins in syncytiotrophoblasts that are not transported to the human fetus is suggestive of nonspecific fluid phase endocytosis. The MHC class I like FcR, similar to the receptor found in neonatal rodent intestine, FcRn, is present intracellularly in human syncytiotrophoblasts, as is its light chain beta 2-microglobulin. The hFcRn is not detected on the apical plasma membrane. The placental hFcRn co-localizes with IgG in syncytiotrophoblast granules. It is likely that hFcRn binds and transcytoses IgG through the syncytiotrophoblast. Protected transfer of IgG may occur within syncytiotrophoblast endocytotic vesicles prior to release in the villous stroma and subsequent translocation into the lumen of fetal stem vessels by uptake and transport in endothelial caveolae.

Hydatidiform mole pregnancy trophoblast extracts differentially suppress interleukin-2-induced proliferation of human T-lymphocytes and PHA-blasts

Immunoregulatory factors of trophoblast origin may partially abrogate maternal immune responses to the fetus during pregnancy. We have previously shown that soluble factors extracted from hydatidiform mole trophoblast suppress interleukin-2 (IL-2)-dependent proliferation of a cloned murine cytotoxic T cell line (CTLL-2). To characterize human T cell responses to this trophoblast extract, we measured the effects of molar tissue extracts (HME) on IL-2-stimulated proliferation of human T-lymphocytes and mitogen (PHA) transformed T-cell blasts (PHA-blasts). HME significantly (P less than 0.05) suppressed T-lymphocyte proliferation in response to 5 and 10 units/ml of IL-2 at 500 and 250 micrograms/ml, while no effect was observed at the 100 micrograms/ml concentration. Suppression by HME of IL-2-stimulated T-cell proliferation was partially overcome by the addition of excess IL-2. HME also suppressed (P less than 0.05) IL-2-stimulated proliferation of PHA-blasts at 500 and 250 micrograms/well at both 5 and 10 units/ml of IL-2. As observed with resting T-cell responses, no suppression of PHA-blast proliferation was observed using 100 micrograms/ml of HME. In contrast to the response of the resting T-cells to excess IL-2, HME suppression of IL-2-stimulated blast proliferation was not affected by increasing the concentration of IL-2. These results indicate that extracts from hydatidiform mole trophoblast contain immunosuppressive factors that block human T-cell clonal expansion by inhibiting the utilization and/or production of IL-2. Furthermore, the effects of HME are not reversed by excess IL-2 when PHA-blasts are reacted compared to resting T-cell responses, which are partially reversed in the presence of excess IL-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Trophoblast-derived immunoregulatory factor: demonstration of the biological function and the physicochemical characteristics of the factor derived from choriocarcinoma cell lines

An immunosuppressive factor released by choriocarcinoma cell lines was analyzed in the present study. It inhibited the proliferative responses of human T cells stimulated by lectins or alloantigens. It also blocked the generation of alloreactive cytotoxic T cells. The suppressive activity of the factor was detected in the responses of the T cells costimulated with 1 nM 12-O-tetradecanoyl phorbol 13-acetate and 1 microM A23187, suggesting the possibility that the factor acted on the intracellular signal transduction in T cells rather than interfering with early events such as T cell receptor signal transduction through cell membranes. Moreover, the factor acted directly on T cell proliferation pathways without activation of suppressor cells but did not act on T cell activation pathways. Taken together, all these findings expanded our previous reports on a factor released by normal trophoblasts, indicating the possible identity of the two factors. The physicochemical properties of the choriocarcinoma-derived factor were examined, and the biological significance of the factor during pregnancy was discussed in this paper.

Murine trophoblast can be killed by allospecific cytotoxic T lymphocytes generated in GIBCO Opti-MEM medium

Previous work in this laboratory demonstrated that a population of cultured midterm murine trophoblast cells are not susceptible to lysis by allospecific cytotoxic T lymphocytes (CTL) generated by standard in vitro protocols. We now report that this trophoblast population is killed, in an MHC-dependent manner, by allospecific CTL generated in GIBCO Opti-MEM, a modified tissue culture medium designed to maintain cell growth and proliferation in the presence of low concentrations of fetal bovine serum (FBS).

Murine trophoblast resists cell-mediated lysis. II. Resistance to natural cell-mediated cytotoxicity

The susceptibility of murine trophoblast cells to natural cell-mediated cytotoxicity has been assessed. Primary short-term cultures of murine trophoblast cells isolated from 14-day placentas were found to be resistant to endogenous and interferon-activated natural killer (NK) cells and natural cytotoxic cells. That the relevant target structures are expressed on the surface of trophoblast cells and accessible to the effectors was demonstrated by their ability to inhibit the lysis of NK-sensitive target cells (YAC-1) in a dose-dependent manner. The lytic resistance of trophoblast cells was unaffected by neuraminidase treatment, inhibition of protein synthesis, or extending the assay time to 12 hr. Moreover, trophoblast cells were resistant to antibody-dependent cell-mediated cytotoxicity when coated with an alloantibody capable of mediating their lysis in the presence of heterologous complement. Neither the preincubation of effector cells in concentrated trophoblast culture supernatants nor the direct exposure of effectors to monolayers of trophoblast cells inhibited their NK lytic activity, indicating that the secretion of a suppressive factor or the direct inactivation of the NK cells was not responsible for the observed resistance to lysis. These observations, together with previous results showing the resistance of trophoblast to cytotoxic T cell-mediated lysis, reveal that murine trophoblast cells possess a resistance mechanism against several forms of cell-mediated lysis. This feature of trophoblast cells at the maternal-fetal interface is likely to play an important role in protecting the fetoplacental allograft from immune rejection.

Major histocompatibility antigens on trophoblast and their regulation: implications in the maternal-fetal relationship

Recent technological advances have provided methods of detecting antigens encoded by the major histocompatibility complex with greater precision, allowing the expression of such antigens on the components of the placenta to be clarified. Of specific interest is the expression of these antigens on trophoblast cells, the fetal-derived epithelial cells that confront maternal blood and tissues at the maternal-fetal interface. It is now clear that the different trophoblast subpopulations differentially express class I antigens, although none appear to express class II antigens. Class I antigens can be induced by exposure to interferons on some populations but apparently not others, suggesting that the regulation of their expression differs for subpopulations of trophoblast cells, depending on gestational stage and location. This restricted expression has important implications for maternal-fetal immune interactions during the different phases of pregnancy and perhaps also bears on physiological functions of the feto-placental unit, such as growth and differentiation.

Suppressor cells in human decidua

Decidual suppressor cells have been found in the murine system. These cells are absent at the implantation sites of interspecies mouse embryos which become infiltrated by maternal cytotoxic cells. Suppression is also deficient at the sites of the spontaneous resorption of fetuses in allomated intraspecies pregnancies. This study was carried out to determine whether similar suppressor cells were present in the decidua during successful human allopregnancies. Decidua was obtained from gestations of 13 to 15 weeks and from term gestations, and the lymphocytes were tested for their ability to suppress the response of their peripheral blood lymphocytes to concanavalin A. Eight of eight 13- to 15-week decidual lymphocytes proved to be suppressive. At term seven of twelve lymphocyte preparations at a lower concentration of cells and six of seven at a higher concentration showed suppression. Suppressor cells appear to be present in human decidua and may play a role in preventing maternal immunologic attack on the allogenic embryo, thereby preventing spontaneous abortion.

Local active suppression by suppressor cells in the decidua: a review

The immunological survival of the antigen-bearing mammalian feto-placental unit is determined by the functional properties of the tissues at the feto-maternal interface. Antigen-specific systemic suppressor mechanisms such as suppressor T cells and nonantigen-specific suppressive serum factors appear not to play a major role in protection of the fetus. A novel type of non-MHC specific suppressor cell accumulates locally in the decidua of successfully allopregnant mice. This decidua-associated suppressor is a small lymphocytic cell possessing cytoplasmic granules, lacks T cell markers, and is deficient in number and activity at the implantation sites of viable xenogeneic Mus caroli embryos gestating in the uterus of Mus musculus animals at the time that maternal lymphoid cells begin to infiltrate the xenoembryos. These Mus caroli embryos subsequently resorb. Further experimental studies suggest that the trophoblast cells associated with successful pregnancy recruit bone-marrow derived maternal non-T suppressor cells to the decidua and thus, by an indirect mechanism, may act to protect the fetus from effector cells of the mother's immune system.

Immunosuppressive properties of murine trophoblast

The modification of the immunological response by murine trophoblast cells of different sources was investigated using the mixed lymphocyte reaction (MLR) and the cell mediated lympholysis (CML) test. MLR between C57BL (H-2b) stimulator splenocytes (mitomycin C treated in the unidirectional MLR) and BALB/c (H-2d) responder lymph node cells were markedly suppressed by trophoblast of ectoplacental cone (EPC) and placental origin. The same in vitro effect was observed with supernatants (SN) of trophoblast cells and with supernatants of blastocysts. Addition of anti-progesterone serum (APS), anti-testosterone serum (RAT), and anti-immunoglobulin serum (RAHIg) in serial dilutions to the trophoblast-MLR system revealed that the immunosuppressive effect of trophoblast giant cells and trophoblast giant cell culture supernatants can be abolished with APS. Identical results were obtained with APS added to immunosuppressive doses of progesterone. CML between C57BL responder lymph node cells and mitomycin C-treated BALB/c stimulator spleen cells was also markedly suppressed when trophoblast of EPC origin was added. A similar suppression of cytotoxic T-cell induction was seen when progesterone was added to the system. The immunosuppressive action of trophoblast as detected in vitro is likely to play an important role in the maintainance of pregnancy by protecting the semiallogeneic conceptus against immune aggression by the maternal immune system.

Interspecific hybrids and chimeras in mice

Interspecific hybrids and chimeras in mammals provide unique tools for investigating problems in genetics and embryology, because of the degree of disparity between the two component genotypes. We have attempted to produce hybrids and chimeras between Mus musculus, the laboratory mouse, and Mus caroli, a wild species of mouse from Southeast Asia. M. musculus and M. caroli do not normally interbreed, although sterile hybrids can be produced at a low rate by artificial insemination. Extrinsic problems of genotypic incompatibility between the fetus and the maternal environment seem to be involved in poor hybrid survival, since M. caroli blastocysts also die when transferred to the M. musculus uterus. Death is associated with the generation of maternal T-cells which are cytotoxic to M. caroli target cells in vitro. It is not yet clear whether this immune response is the primary cause of death or is secondary to breakdown of some other components of the fetal-maternal interaction. It is clear, however, that it is the trophoblast layer that mediates survival or death of the foreign embryonic cells in the M. musculus juterus, since M. caroli inner cell mass cells can survive to term after injection into M. musculus blastocysts: Viable interspecific chimeras result. Even more convincing evidence is provided by the production of viable M. caroli offspring by trophoblast vesicle reconstitution using trophoblast of M. musculus genotype and inner-cell mass of M. caroli type. Studies of properties of isolated trophoblast tissues have indicated that M. caroli trophoblast may differ from M. musculus in both its antigenic and immunosuppressive properties. Elucidation of trophoblast-uterine interactions in these various interspecific pregnancies is being aided by the development of an in situ marker system, which can distinguish cells of the two species in sectioned material by in situ hybridization with a M. musculus satellite DNA probe. This same marker is also proving a very powerful tool for analyzing cell lineage development in chimeras.

In vitro susceptibility of mouse placental trophoblast to cytotoxic effector cells

The susceptibility of mouse placental cells to hyperimmune cell killing directed against paternal combined H-2 and non-H-2 antigens was investigated using [3H]uridine as a terminal label in an in vitro cell-mediated microcytotoxicity test. The stage of development of the conceptus from which the short-term placental cell monolayers were prepared determined their susceptibility to immune cell lysis. Cultures from whole placentae taken at 9 days post-coitum (p.c.) were not significantly affected whereas similar monolayers prepared at 10.5 days p.c. or later underwent extensive destruction. Embryonic fibroblasts were susceptible at all stages examined from 9-16 days p.c. The onset of susceptibility correlates with the reported appearance of H-2 antigens on the placenta during ontogeny. All cultures of dissected populations of 13-day p.c. placental spongiotrophoblast were susceptible but only 70% of those of labyrinthine trophoblast. It is suggested that of the two major trophoblastic components of the mouse placenta the spongiotrophoblast expresses antigens that render it vulnerable to maternal immune attack whilst the labyrinthine trophoblast is only weakly or non-antigenic, with the observed killing being due largely to contamination of these cultures by antigenic foetal mesenchymal elements. Since failure to express appropriate target antigens cannot be the reason for the in vivo survival of the spongiotrophoblast it must be presumed that some form of immunoregulatory mechanism(s) is responsible for the maintenance of the foeto-placental allograft.

Histological and immunological studies of post implantation death of Mus caroli embryos in the Mus musculus uterus

Mus caroli blastocysts surgically transferred to the Mus musculus uterus implant and develop successfully during the first 9.5 days of gestation. At this time, the trophoblast giant cell area becomes infiltrated with lymphocytes and, subsequently, massive hemorrhage occurs, associated with embryo death. This process is specific for the xenogeneic embryos and does not affect adjacent allogeneic embryos present in the same uterus. Cells taken from the resorbing tissues contain a population of large Thy 1+, Lyt 1+, Lyt 2+ cytotoxic cells capable of lysing Mus caroli concanavalin A blasts in vitro. It is suggested that failure of the Mus caroli embryos in the Mus musculus uterus is mediated by the maternal immune system and that the xenogeneic blastocyst transfer system provides a suitable animal model system for studies of mechanisms that prevent rejection of the fetal allograft.

Reproductive histories in a Norwegian twin population: evaluation of the maternal effect in early spontaneous abortion

An evaluation of the maternal effect on spontaneous abortion and the genetic contribution to various reproductive variables was made using like-sexed twins born between 1915–1946. Health and reproductive questionnaires were sent to 2,365 twin pairs listed in the Norwegian Twin Registry. Zygosity was determined by a questionnaire which proved to be 98% accurate in discriminating between monozygotic (MZ) and dizygotic (DZ) twins. Verification of the zygosity questionnaire was accomplished by blood cell marker zygosity determination in 200 twin pairs. Data from 428 monozygotic twin pairs (174 male pairs and 254 female pairs) were analyzed by a new model for qualitative traits and a striking maternal effect was found. The results suggested that over 54% of all women may belong to a high risk group who have approximately a 13% risk of early fetal loss. The incidence of first trimester abortions and spontaneous abortion reported by a sample of 915 like-sexed twin pairs and spouses was .079 and .089, respectively; there were no significant differences between male and female pairs.

Other reproductive variables were studied in both MZ and DZ twins including the age of menarche and menopause, the age at marriage and birth of the first child, and the interval between marriage and the first birth. These variables were examined for evidence of genetic effects and secular trends. The mean age of menarche had decreased significantly between the years 1915–1935 and 1936–1946. The secular trend appeared to be environmental in nature and accounted for more than 7% of the overall variation in age of menarche. Sixty-five percent of the variation in the age of menarche was attributed to genetic factors. The mean age of marriage and the mean age at the first birth decreased significantly between 1915–1935 and 1936–1946. Twins born between 1936–1946 also reported fewer pregnancies than did twins born between 1915–1946, but this was statistically significant among MZ twins only; no significant difference in the frequency of spontaneous abortions was found between the 1915–1935 and the 1936–1946 groups.

Although there were occasional groups in which differences were statistically significant, no general trends were identified in comparing couples who reported a spontaneous abortion with those who did not. Traits compared were: the age of menarche, age of marriage, age at first birth, the interval between marriage and first birth and the mean present age of the twins and spouses. Couples reporting a first trimester spontaneous abortion had significantly more total pregnancies than those not reporting a spontaneous abortion. Unaffected pregnancies were also significantly more numerous in couples with a spontaneous abortion compared to those without, suggesting over-compensation for fetal loss.

A maternal effect in spontaneous abortion was indicated by the correlation coefficients found; significant positive correlations were found in both MZ and DZ females but not in males. For total pregnancies and unaffected pregnancies, MZ twins, both male and female, had significant correlation coefficients while DZ twins did not.

Trophoblast transferrin and transferrin receptors in the host--parasite relationship of human pregnancy

Transferrin and specific transferrin receptors are demonstrated on the microvillous surface of syncytiotrophoblast in human immature and term placentae by immuno histological techniques with the use of light and electron microscopy. That the distribution of transferrin is limited to the materno-foetal interface supports the hypothesis that binding of maternal transferrin to trophoblast receptors is involved in the process of iron transport to the foetus. Parallel studies with baboon placentae demonstrate the presence of trophoblast receptors which bind both baboon and human transferrin, thereby putting forward an experimental model which might be used to test the biological significance of placental transferrin receptors in primates. In addition, investigation of a large number of human cell lines shows that many transformed cells, but no normal cells (such as blood lymphocytes) or cells from primary culture (such as neonatal foreskin fibroblasts), possess the ability to bind transferrin to their membranes. These findings suggest that transferrin receptors may play important biological roles in addition to that of iron transport from mother to foetus. One such role could be the limitation of iron in intervillous spaces, thus depriving iron-requiring microorganisms of iron, hence serving as a non-specific factor of resistance for placentae. Another role for foetal transferrin receptors on trophoblasts could be to bind maternal transferrin at the materno-foetal interface, thus frustrating maternal immunosurveillance. This is similar to a mechahism used by schistosomes in the host-parasite relation where host proteins are bound by the parasite to escape immunological recognition. The presence of transferrin receptors on transformed cells suggests that this mechanism might also be employed by tumour cells. Finally, in view of previous studies which show that transferrin is required by stimulated lymphocytes to pass from the G1 to the S phase of cellular replication, it is proposed that trophoblast transferrin receptors could limit the amount of transferrin in intervillous spaces and thus impede the proliferation and possible cytotoxicity of maternal activated lymphocytes at the materno-foetal interface.

The immunobiology of placentation

A review of the current theories on the nature of the placental allograft and the evolution of placentation in the presence of a cellular immune response highlights the inability of current hypotheses to explain the success of both invertebrate and vertebrate placentation. Only one theory -- "the anatomical separation of the fetus from the mother" -- appears relevant. How this separation might develop during implantation is discussed.

Decidual extracts suppress antibody response in vitro

Extracts of decidual tissue produced in pseudopregnant rats were found to suppress in vitro antibody response to alpha-2,4-dinitrophenyl-polylysine. The peak levels of both the total antibody response and the 2-mercaptoethanol-resistant fraction were reduced. Extracts prepared in a similar manner from uteri of normal untreated or pseudopregnant rats did not exert such an effect.

Selection at implantation and longevity. A tentative theory

Women enjoy a superior longevity, possibly at the price of a heavy loss of female conceptuses at an early stage of gestation. An immunological mechanism is proposed. A theory of selection at implantation is developed and generalized which leads to a new approach of longevity.

Association of genetic polymorphisms with fertilization in the chicken

Associations between fertilization rate and genotypes at four polymorphic loci were studied in three relatively non-inbred populations of Light Sussex chickens. In sires the genotypes tested were at theB blood-group locus only; in dams, at theB locus and three egg-white loci. Data were available for purebred matings of related substrains 6D and 6F and the ancestor strain 6 from which they were derived and for crossbred matings of 6D and 6F by two related Rhode Island Red/New Hampshire strains.In analyses of variance by dam genotypes within sires, no locus or combination of loci had a significant effect on fertilization rate. In analyses by sire and damB blood-group genotypes, no significant effects were found in 6F. SireB genotypes showed a very significant effect (P<0.001) on fertilization rate in 6D, and in 6. The latter effect was not fully acceptable since there was a significant (P<0.02) sirex damB genotypes interaction effect in 6. This interaction took the form of a lowered fertility in matings where sire and dam had the sameB genotype. The significant main effect in 6D was due to significant differences between the fertilization rates of the three most frequent sire genotypes. The same differences were not found in the other two strains. Similarly, significant sireB genotype differences in the Rhode Island Red/New Hampshire mates of 6F were not repeated in those of 6D.Combination of this result with those from our previous work with embryonic mortality in these strains is still insufficient fully to explain the continued segregation of four alleles at theB blood group locus.