Some parameters of lymphocyte antibody activity through pregnancy and further eluates of placental material

A Child's HLA-DRB1 genotype increases maternal risk of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) disproportionately affects women of reproductive age. During pregnancy, women are exposed to various sources of fetal material possibly constituting a significant immunologic exposure relevant to the development of SLE. The objective of this study was to investigate whether having any children who carry DRB1 alleles associated with SLE increase the risk of maternal SLE. This case-control study is based on the University of California, San Francisco Mother-Child Immunogenetic Study and from studies at the Inova Translational Medicine Institute. Analyses were conducted using data for 1304 mothers (219 cases/1085 controls) and their respective 1664 children. We selected alleles based on their known association with risk of SLE (DRB1*03:01, *15:01, or *08:01) or Epstein-Barr virus (EBV) glycoproteins (*04:01) due to the established EBV association with SLE risk. We used logistic regression models to estimate odds ratios (OR) and 95% confidence intervals (CI) for each allele of interest, taking into account maternal genotype and number of live births. We found an increase in risk of maternal SLE associated with exposure to children who inherited DRB1*04:01 from their father (OR 1.9; 95% CI, 1.1-3.2), among *04:01 allele-negative mothers. Increased risk was only present among mothers who were positive for one or more SLE risk-associated alleles (*03:01, *15:01 and/or *08:01). We did not find increased risk of maternal SLE associated with any other tested allele. These findings support the hypothesis that a child's alleles inherited from the father influence a mother's subsequent risk of SLE.

Association of maternal anti-HLA class II antibodies with protection from allergy in offspring

BACKGROUND

Recent studies have suggested that the birth order effect in allergy may be established during the prenatal period and that the protective effect may originate in the mother. HLA class II disparity between mother and foetus has been associated with significantly increased Th1 production. In this study, we investigated whether production of HLA antibodies 4 years after pregnancy with index child is associated with allergic outcomes in offspring at 8 years.

METHODS

Anti-HLA class I and II antibodies were measured in maternal serum (n = 284) and levels correlated to numbers of pregnancies and birth order, and allergic outcomes in offspring at 8 years of age.

RESULTS

Maternal anti-HLA class I and II antibodies were significantly higher when birth order, and the number of pregnancies were larger. Anti-HLA class II, but not class I antibodies were associated with significantly less atopy and seasonal rhinitis in the offspring at age 8 years. Mothers with nonatopic (but not atopic) offspring had a significant increase in anti-HLA class I and II antibodies with birth order.

CONCLUSION

This study suggests that the 'birth order' effect in children may be due to parity-related changes in the maternal immune response to foetal antigens. We have observed for the first time an association between maternal anti-HLA class II antibodies and protection from allergy in the offspring. Further work is required to determine immunologically how HLA disparity between mother and father can protect against allergy.

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.

Modulation of Allospecific CTL Responses During Pregnancy in Equids: An Immunological Barrier to Interspecies Matings?

Maternal immune recognition of the developing conceptus in equine pregnancy is characterized by the strongest and most consistent alloantibody response described in any species, a response directed almost exclusively against paternal MHC class I Ags. This work investigated the cellular immune response to paternal MHC Ags in pregnant and nonpregnant horses and donkeys, and in horses carrying interspecies hybrid mule conceptuses. We observed profound decreases in classical, MHC-restricted, CTL activity to allogeneic paternal cells in peripheral blood lymphocytes from both horse mares and donkey jennets carrying intraspecies pregnancies, compared with cells from nonpregnant controls. This is the first evidence in a randomly bred species for a generalized systemic shift of immune reactivity away from cellular and toward humoral immunity during pregnancy. Surprisingly, mares carrying interspecies hybrid mule conceptuses did not exhibit this transient, pregnancy-associated decrease in CTL activity. The failure of interspecies pregnancy to down-regulate cellular immune responses may be a heretofore-unrecognized, subtle barrier to reproductive success between species.

Human placental Fc receptors and the trapping of immune complexes

Monomeric maternal antibodies are transmitted to the fetus, but most immune complexes are trapped in the placental stroma. The receptors responsible for trapping immune complexes appear to be Fc gamma RIa, Fc gamma RIIa, and Fc gamma RIIIa on stromal macrophages, and Fc gamma RII on fetal capillary endothelial cells.

Human placental Fc receptors and the transmission of antibodies from mother to fetus

During human pregnancy, maternal IgG is transported across the placenta to the fetus. On the way, some maternal antibodies against fetal antigens are removed as immune complexes. The placenta contains several known Fc receptors and also other proteins that bind immunoglobulins. A consideration of the binding properties and distribution of these proteins suggests that the neonated Fc receptor (FcRn) transports IgG across the syncytiotrophoblast, and possibly the fetal blood vessel endothelium. Fc gamma RI, Fc gamma RII and Fc gamma RIII on Hofbauer cells in the stroma probably clear immune complexes, together with Fc gamma RII on endothelial cells.

Is restricted antigen presentation the explanation for fetal allograft survival?

Mammalian embryos express paternal histocompatibility antigens which make them potential targets for the maternal immune system. The trophoblast is a major histocompatibility complex (MHC) antigen-negative barrier between mother and fetus which facilitates movement of antigenic molecules but prevents traffic of antigenic cells and is itself unable to present antigen. Gary Wood suggests that the lack of antigen presentation requirements for MHC class I-restricted T-cell responses prevent generation of paternal-antigen directed cell-mediated immunity.

The normal fetomaternal immune relationship

The antigenic status of the preimplantation embryo is ill-defined and there are no clearly recognized maternal immune reactions against this early stage of development. Following implantation, the pregnant female shows evidence of immune recognition of her intrauterine allogeneic conceptus. In a proportion of pregnancies, particularly in multiparous women, there are maternal cytotoxic antibodies exhibiting specificity for the paternally inherited HLA antigens of the fetus. When these are undetectable there may be other antibodies that are non-complement fixing and non-cytotoxic or antibodies that are not present as free molecules and incapable of identification in conventional assays. Anti-HLA antibodies pose no threat to the fetus, principally owing to their absorption by the placenta and, very likely, the harmless binding of any that do reach the fetal circulation. No potentially deleterious cytotoxic T lymphocyte generation occurs in most pregnancies. The extent to which this is due to maternal immunoregulatory control processes is not yet established. The fetal trophoblast is able to act as a protective barrier by virtue of unique properties, including a lack of conventional class I and class II HLA molecules, that render it insusceptible to immune attack. The nature and significance of any maternal recognition of non-HLA antigens on trophoblast await elucidation. Maternal immune cell traffic across the placenta occurs only at a very low level, if at all, in normal pregnancy. This may take place to a greater degree in some of the rare instances of fetal graft-versus-host disease, but this is complicated by the associated fetal immunodeficiency. Maternal IgG antibodies are transmitted across the placental trophoblast by receptor-dependent mechanisms to provide immediate protection for the neonate against environmental pathogens. Leakage of fetal erythrocytes, leukocytes and platelets into the maternal circulation can elicit IgG isoantibodies that take advantage of the same mechanisms to gain access to the fetus, with pathological consequences. Autoantibodies in women with various disease states may similarly pass into the fetus but these normally produce only mild and transient effects. The development of the fetal immune system begins at an early stage of gestation. It is competent to respond to intrauterine infections from as early as 12 weeks and has full functional potential at birth. Maternally acquired IgG is available for up to 9 months of life until the infant's own immune system has been adequately primed and activated following first exposure to specific antigens. The normal fetomaternal immune relationship represents a remarkable harmonious association between two genetically disparate individuals.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunological aspects of pre-eclampsia

The first pregnancy preponderance and apparent partner specificity of pre-eclampsia suggest that it might have an immune aetiology. The pathogenesis of pre-eclampsia is undefined although it is clear that it is a placental disorder. The maternal syndrome appears to be mediated by placental ischaemia secondary to spiral artery insufficiency. This leads to a hypothesis that pre-eclampsia is a two-stage disease. The first comprises processes that limit the size of the spiral arteries (poor placentation) or obstruct them (acute atherosis). Either or both may have immunological causes although there is no direct evidence. Factors limiting placentation could involve maternal immune intolerance of the fetal allograft, which in their most extreme expression could lead to immunologically mediated abortion. Thus pre-eclampsia may be part of a wider spectrum of pregnancy loss secondary to poor maternal immune accommodation of her genetically disparate fetus. The second stage involves the consequences of the ensuing placental ischaemia. The syndrome is currently tentatively ascribed to diffuse maternal endothelial dysfunction. There is less reason to invoke immunological mechanisms in the second stage although neutrophil activation could explain generalized endothelial damage. It should be clear that these conclusions are provisional and that the greatest need is for more investigation to eliminate the uncertainty which clouds our concepts.

Increasing quantity of maternal immunoglobulin G in trophoblastic tissue before the onset of normal labor

While levels of maternal immunoglobulin G (IgG) increase in the fetal circulation during the third trimester, actual trophoblastic concentrations have not been extensively studied. To investigate this process, placentas from 71 patients with gestational ages between 26 and 42 weeks were examined by means of a peroxidase-antiperoxidase immunostaining technique specific for IgG. Linear regression revealed a significant increase in antibody with advancing gestational age (r = 0.36, p less than 0.01). In addition, placentas from patients in spontaneous term labor revealed a significantly higher antibody level when compared with those of patients at term delivered electively before the onset of labor (mean +/- SEM 2.6 +/- 0.2 vs 1.7 +/- 0.3, p less than 0.02). Patients in premature labor failed to demonstrate this increase in antibody staining. One possible explanation for these findings is an enhanced recognition of the fetal trophoblastic tissue by the maternal immune system at term. It also suggests immunologic factors may play an important role in the initiation of normal labor.

Fetus as an allograft: noncytotoxic maternal antibodies to HLA-linked paternal antigens

A cellular enzyme-linked immunospecific assay (CELISA) was used to monitor maternal humoral responses in human pregnancy. Non-cytotoxic IgG antibodies to paternal lymphocytes were detected in sera from 6 of 20 normal first trimester primigravidae and 6 of 13 multiparae. No antibody activity against lymphocytes from their partners was detected in sera from any of the 15 nulliparous women. The differences in antibody response between primigravidae and nulliparae (P = 0.024) and between multiparae and nulliparae (P = 0.005) were statistically significant. Lymphocytotoic antibodies to T- and B-lymphocytes were present in sera from three multiparae, but from none of the women in the other two groups. Family studies indicated that the non-cytotoxic pregnancy-associated maternal antibodies were directed to HLA-linked antigens (P less than 0.001). Evidence obtained using cell panels and platelet absorption suggested, however, that these antibodies were not directed to the currently recognized HLA specificities (HLA-A, -B, -C, or -DR).

The separation of the antibody and antigen components of immune complexes formed during normal human pregnancy

By the manipulation of the fractionation conditions of a series of protein A affinity columns it was possible to separate the antibody and antigen components of the immune complexes formed in the serum during normal human pregnancy. The two components were partially characterised in order to determine that they were separate biological entities. The IgG immunoglobulin component possessed antibody activity directed against the outer layer of the placenta, the syncytiotrophoblast. The antigen component was of apparent syncytiotrophoblast origin and consisted of a protein with two major polypeptides of Mr 63 kDaltons and 31 kDaltons.

Anti-trophoblast antibody responses during normal human pregnancy

During the course of a normal uncomplicated human pregnancy the mother generates an antibody response directed against determinants present on the plasma membrane of the outer fetal layer of the term placenta, the syncytiotrophoblast. The response, measured by an ELISA that utilises syncytiotrophoblast plasma membrane as the antigenic target, is predominantly IgG in nature, but with a minor contribution from IgM molecules. Maximum responses were observed during the first trimester and the levels gradually declined as the pregnancy progressed. On a population basis, this antibody response profile was mainly restricted to first and second pregnancies, although anti-trophoblast antibody responses could be detected in multiparous women but with a greatly reduced incidence compared with primipara. Mechanisms to account for these observations are discussed. Throughout, the anti-trophoblast antibody levels detected in pregnancy sera were compared with the background levels which were observed in sera obtained from males and nulliparous non-pregnant females.

An ELISA for the detection of maternal anti-trophoblast antibodies in human pregnancy

An ELISA has been developed which is able to detect antibodies directed against determinants present on the plasma membrane of the outer layer, the syncytiotrophoblast, of term placentae. The IgG and IgM anti-trophoblast antibodies are present in the sera of women during the course of a normal pregnancy. The ELISA was based on the use of syncytiotrophoblast plasma membranes as the antigenic targets and utilised a developing antiserum conjugated to the bacterial enzyme urease. Although the assay was simple and reproducible, its viability was dependent on several factors including the stability of the antibodies and the proper preparative techniques for the production of the plasma membranes. Failure to adhere to the correct procedures resulted in an inferior non-viable assay.

The formation of immune complexes in primiparous and multiparous human pregnancies

Using a recently developed ELISA, antibodies were detected in maternal sera with reactivity directed against determinants present on the plasma membrane of the outer layer of the placenta, the syncytiotrophoblast. The anti-trophoblast antibodies were present in maternal sera in the form of "free" antibodies and "immune complex" antibodies. Examination of the sera throughout gestation and from successive pregnancies revealed that the generation of anti-trophoblast antibodies and the formation of immune complexes was predominantly a first pregnancy and early second pregnancy event, with very little activity detectable in later pregnancies. It is proposed that immune recognition occurs in a first pregnancy, which generates some form of immunosuppression that involves the activation of suppressor memory cells.

Transcriptional control of HLA-A,B,C antigen in human placental cytotrophoblast isolated using trophoblast- and HLA-specific monoclonal antibodies and the fluorescence-activated cell sorter

Human placental cell suspensions prepared by trypsin digestion were analyzed with several monoclonal antibodies on a multiparameter fluorescence-activated cell sorter (FACS). Five distinct cell populations were isolated on the basis of size and quantitative differences in the coordinate expression of cell surface antigens detected by monoclonal antibodies against an HLA-A,B,C monomorphic determinant (MB40.5) and against human trophoblasts (anti-Trop-2). By FACS analysis and after sorting we clearly identified the major cell population as cytotrophoblasts based on several independent criteria, including presence of trophoblast-specific surface antigens, Trop-1, and Trop-2; absence of all HLA class I, class II, and beta 2-microglobulin (beta 2m) antigens; absence of the pan-leucocyte and monocyte antigens, HLe1 and LeuM1, respectively; presence of Y-chromatin in a male placenta; presence of placental and not liver alkaline phosphatase; and a large, mononuclear morphology. These procedures provide a reproducible method for obtaining highly purified human cytotrophoblast populations for further studies. We measured by molecular hybridization (RNA or Northern blots) the HLA-A,B,C and beta 2m mRNA in total RNA extracted from sorted cytotrophoblasts. We find that normal human cytotrophoblasts have extremely small amounts of HLA-A,B,C mRNA: approximately 300 times less than that in the lymphoid cell line LCL-721 or normal lymphocytes. In contrast, they have approximately 11% the level of beta 2m mRNA present in LCL-721 cells. Thus, HLA-A,B,C antigen expression on human cytotrophoblasts is limited by the level of HLA heavy chain mRNA.