Possible protecting role of maternal immunoglobulins on embryonic development in mammals

An immunoreactive theory of selective male affliction

Males are selectively afflicted with the neurodevelopmental and psychiatric disorders of childhood, a broad and virtually ubiquitous phenomenon that has not received proper attention in the biological study of sex differences. The previous literature has alluded to psychosocial differences, genetic factors and elements pertaining to male “complexity” and relative immaturity, but these are not deemed an adequate explanation for selective male affliction. The structure of sex differences in neurodevelopmental disorders is hypothesized to contain these elements: (1) Males are more frequently afflicted, females more severely; (2) disorders arising in females are largely mediated by the genotype; in males, by a genotype by environment interaction; (3) complications of pregnancy and delivery occur more frequently with male births; such complications are decisive and influence subsequent development. We hypothesize that there is something about the male fetus that evokes an inhospitable uterine environment. This “evocative principle” is hypothesized to relate to the relative antigenicity of the male fetus, which may induce a state of maternal immunoreactivity, leading either directly or indirectly to fetal damage. The immunoreactive theory (IMRT) thus constructed is borrowed from studies of sex ratios and is the only explanation consistent with negative parity effects in the occurrence of pregnancy complications and certain neurodevelopmental disorders. Although the theory is necessarily speculative, it is heuristic and hypotheses derived from it are proposed; some are confirmed in the existing literature and by the authors' research.

Inhibition of implantation of hamster embryos by lectins

In order to test their effects on implantation, lectins (Con A and WGA) were infused into one horn of the uterus of each female hamster aged between 10 and 14 weeks at day 3 of pregnancy (D3). Con A was given to three groups of 10 animals each at dosages of 100, 200 and 400 micrograms/10 microliter normal saline (NS)/animal, and WGA to four groups of animals at dosages of 20, 50, 100 and 200/10 microliter NS/animal. Control groups consisted of untreated animals and animals treated with saline. On D8, laparotomy was performed and the number of fetuses were counted. In untreated and NS-treated groups the number of fetuses were 6.9 and 6.8 per horn, which were not significantly different. In Con A-treated groups, at dosages of 100, 200 and 400 micrograms the number of fetuses were 2.2, 2.5 and 2.1 per horn, respectively. By contrast, in WGA-treated groups no implantation was detected, except at the dosage of 20 micrograms, in which 1.1 fetuses per horn was observed. To study the mechanism of inhibition, another three groups of animals were similarly treated with NS, 100 micrograms Con A and 50 micrograms WGA/10 microliter NS/animal, respectively. On D4 at 1300-1400 h, uterine lumens were flushed to collect unimplanted blastocysts. No blastocyst was found in NS- and Con A-treated groups, whereas 6.2 blastocysts with complete zona pellucida were collected per horn in WGA-treated group. Histologically, Con A caused vacuolization in epithelium and edema in the stromal layer of endometrium. However, such changes were not observed in WGA-treated uteri.

Allosensitization in tumor therapy and prophylaxis, and in female contraception--a prospect for clinical use

A hypothesis is presented on the possible role of allosensitization in therapy and prophylaxis of human tumors, and in human female contraception. The essence of the proposed treatment of human malignancies is allosensitization with allogeneic white blood cells by means of application of two blood transfusions from normal healthy donors within a certain time interval to patients with invasive or metastasizing cancer. The therapy should be accompanied by immunoglobulins, bacterial toxins and a single dose of cytostatics. In the case of a successful tumor regression a prophylaxis of recurrence should be made with two doses of intradermally injected allogeneic lympho-leucocytic concentrates mixed with bacterial toxins; such treatment might also be effective in tumor prophylaxis, or in long-lasting contraception in women. The hypothesis is supported by recent literature as well as by our recent results in the area of cell-mediated control of tissue proliferation, fetal allograft survival or tumor development. It is concluded that tumor rejection can be mediated not only by the direct effect of anti-tumor drugs but more effectively by the organisms mechanisms responsible for removal of undesirable tissue.

The secretory immune system in the uterus of the pregnant rat: production of secretory component by uterine tissues

Secretory component (SC) was measured in amniotic fluid, fetal serum, and maternal serum and compared with SC production during in vitro culture of uterine tissue segments from pregnant rats. The concentrations of SC in amniotic fluid did not change between days 14 and 20 of pregnancy. Similarly, there was no change in maternal or fetal serum during pregnancy, although, the levels of SC in sera were consistently higher than those in amniotic fluid. When uterine segments were incubated in vitro, release of SC was greater in the absence of cycloheximide than in the presence of cycloheximide at all stages of pregnancy. In contrast to SC values in amniotic fluid, however, SC production by uterine tissue changed markedly during pregnancy. SC levels were low during early pregnancy (day 7 post coitus) and increased to levels found in non-pregnant diestrous rats just prior to parturition (day 20). The findings suggest that the endocrine balance during pregnancy may play a central role in regulation of the uterus immune system. The pattern of SC release may reflect a need both to ensure protection of the fetus from the IgA immune system in early pregnancy and to prevent maternal infection during parturition by reactivation of this system.

Habitual abortion: parental sharing of HLA antigens, absence of maternal blocking antibody, and suppression of maternal lymphocytes

The immunologic responsiveness of eight women who habitually abort has been investigated. All shared an HLA-A or B antigen with their husbands. Sharing of an HLA-DR antigen was found in seven couples, one of which also had a second DR antigen in common. The probability for this high frequency of HLA-DR sharing is negligible (p = 0.0004), as calculated from the antigen frequencies among Europeans. Cells from the woman with two shared DR antigens displayed a minor response to her husband's cells but reacted strongly to control cells, whereas the other women's cells reacted normally to cells from both their husbands and controls in one-way mixed lymphocyte culture (MLC). Only minor cytotoxicity was displayed by women's cells in a direct cell-mediated lympholysis (CML) assay, but they mounted normal cytotoxic responses against both husbands' cells and control cells in an amplified CML assay. The sera from six of the habitually aborting women displayed no blocking activity in one-way MLC, and seven of them had no cytotoxic antibodies. Cells from all habitual aborters were suppressed in two-way MLC by cells from husbands and most controls. We hypothesize that increases in HLA compatibility between mother and fetus and in maternal susceptibility to suppressive influences are in some way linked to a deficiency in the development of antifetal antibody during pregnancy. As a consequence, the fetus may be deprived of the protection by maternal blocking antibody, which may allow maternal cytotoxic reactions to cause abortion.

Current trends in reproductive immunology: an overview

Over the past decade has come general recognition that, directly or indirectly, immunology intrudes into nearly every aspect of mammalian reproduction. Charles Darwin's notion that the profligacy of women led to reduced fertility gained plausibility with the subsequent discovery of the auto- and alloantigenicity of spermatozoa and of testicular material. From this observation arose the reasonable expectation that immunological control of fertility may be feasible. Discovery of the importance of natural transfer of immunity from mother to offspring, the ontogeny of the immune response, and recognition that pregnancy is an almost consistently successful violation of the "laws of transplantation' are only a few highlights or components of the burgeoning, multifaceted field we have come to recognize as the immunology of reproduction. An overview of this subject is here presented with regard to its evolutionary origins, its accomplishments, its current trends, and some of its potentialities. The immunology of reproduction has not developed in isolation; in recent years it has benefited enormously from developments in other fields, and in its turn it has exerted its own impact on other disciplines, especially on transplantation. The present preoccupation of many immunologists with immunoregulation stems largely from independent discoveries in the realm of reproductive immunobiology - the etiology of Rhesus disease and its prophylaxis, and the principle of immunological tolerance, from investigations on the peculiarities of dizygotic twins in cattle.

Humoral immune responses in murine pregnancy. I. Anti-paternal alloantibody levels in maternal serum

The kinetics and properties of anti-paternal alloantibody produced by female C57BL(H-2b) mice in response to mating with CBA(H-2k) males have been investigated using an immunobead adsorption assay. No alloantibody was ever detected in the first pregnancy or post-partum period. 72% of females exhibited a humoral response in their second pregnancy, detectable from day 16 or 17 post-coitum, and almost all females responded in their third pregnancy. Column chromatographic and immunoelectrophoretic analysis showed that the alloantibody was IgG. Although passive transfer experiments suggested similar stability characteristics to those of cytotoxic antibody induced by experimental hyperimmunization, the pregnancy-induced alloantibody did not exhibit complement-dependent cytotoxicity. The findings are discussed in relation to the nature of the immunogenic stimulus from the conceptus and the regulation and possible function of the humoral immune response in allogeneic pregnancy.

Expression of retrovirus-related antigen in pregnancy. II. Cytotoxic and blocking specificities of immunoglobulins eluted from the placenta

Immunoglobulins, mostly of the IgG class, were detected in eluates of the placenta of 75% of 50 healthy women in their first or second pregnancy, 92% of 30 women with more than two pregnancies, and 87% of 23 pre-eclamptic patients. The immunoglobulins were assayed for complement-dependent cytotoxicity on human and monkey cell-lines, as well as on the same cells chronically infected with either Mason-Pfizer Virus (M-P V) or Baboon Endogenous Virus (BeV). The frequency of cytotoxic reactions was very low, except with immunoglobulins from the pre-eclamptic placentae, where one third of the samples lysed virus-infected cells with occasional killing of virus-free cells. All placental immunoglobulins which were not cytotoxic were then assayed for blocking activity by testing whether they could compete with the action of anticellular sera of virus-free cells, or with the toxic effect of antiviral sera on virus producing cells. 64% of the immunoglobulins from normal placentae competed with antiviral antibodies while only 17% blocked the action of anticellular sera. The frequency of blocking immunoglobulins was no greater in eluates from pre-eclamptic placentae. The data indicate that the placenta possesses retrovirus antigen sites which bind blocking antibodies in normal pregnancy and complement-dependent cytotoxic antibodies in pre-eclampsia.

In vitro foeto-maternal lymphocyte responses at delivery: no gross changes in MLC and PLT responsiveness

The reactivity of peripheral blood mononuclear cells of mothers and their newborns in mixed lymphocyte cultures (MLC) and primed lymphocyte typing (PLT) was tested. The primary MLC tests did not demonstrate any altered kinetics or suppression of the mother's lymphocytes towards the cells of her newborn, or vice versa. In most cases, the bidirectional MLC between maternal and newborn cells was found to be normal. Maternal lymphocytes could, however, be primed in vitro to cells from their newborn, and demonstrated a somewhat better specificity for HLA-D determinants than paternal cells similarly primed, indicating that some priming may have occurred in vivo during pregnancy.

Evidence for the role of the maternal immune system in balancing the sex ratio in mice

Two experiments have been conducted to verify the effect of maternal preimmunization to H-Y antigen on the secondary sex ratio in C57Bl/6 mice. In accord with the theoretical model previously proposed, it was found that extensive immunization to H-Y antigen following splenectomy resulted in a significant increase in sex ratio (males/females) without affecting litter size. Litter size was also not correlated to sex ratio. The data from both experiments suggest that splenectomy alone or restimulation to H-Y antigen (after 30 days) both act to decrease sex ratio. It is concluded that the maternal immune system plays a limited, but significant, role in maintaining the normal sex ratio in mice.

Birth order and intelligence: an immunological interpretation

The literature indicates that the IQs and school performance of children tend to decline with increasing order of birth. A hypothesis is here presented that the effect of birth order upon intellectual performance may result from an increasing probability of maternal immune attack upon the fetal brain in utero with order of parity. In support of this hypothesis, evidence is adduced from the literature that the fetal brain is antigenic, that fetal antigens may reach the immune system of the mother, that the incidence of maternal sensitization to fetal antigens increases with parity, that antibodies may readily cross the placenta and reach the fetal brain, that antibodies can be highly teratogenic, and that certain antibodies may damage, in a lasting way, the structure, function, and learning capacity of brains in experimental animals and human infants.