Anti-fetal allo-antibody in the pregnant female

Regulatory T-cells in pregnancy: historical perspective, state of the art, and burning questions

In this review, we first revisit the original concept of "suppressor T-cells" in pregnancy, put it in a historical perspective, and then highlight the main data that licensed its resurrection and revision into the concept of "regulatory T-cells" (Tregs) in pregnancy. We review the evidence for a major role of Tregs in murine and human pregnancy and discuss Treg interactions with dendritic and uterine natural killer cells, other players of maternal-fetal tolerance. Finally, we highlight what we consider as the most important questions in the field.

Tolerance to the foetal allograft?

In this review, we will detail the concept of tolerance and its history in reproductive immunology. We will then consider whether it applies to the foetal-maternal relationship and discuss the mechanisms involved in non-rejection of the foeto-placental unit.

The Th1/Th2 paradigm: still important in pregnancy?

The enunciation of the T helper 1/T helper 2 (Th1/Th2) paradigm in pregnancy has represented a major step forward in our understanding of physiological and pathologic materno-foetal relationship. However, recent developments in studies of the implantation process and in the emergence of the uterine vascular bed and its control by natural killer cells and cytokines suggest that one must go beyond this hitherto useful scheme. In this review, we replace the emergence of the paradigm in its historical context and then emphasises what it does explain and what it no longer account for. A final reappraisal of the paradigm is suggested.

The immunological problem of pregnancy: 50 years with the hope of progress. A tribute to Peter Medawar

This article is a tribute to the late Sir Peter Brian Medawar for his pivotal contribution in 1953 to the establishment of the field of Reproductive Immunology, with a brief and selective assessment of the progress made during the ensuing 50 years towards elucidation of the mechanisms responsible for the paradoxical survival of the conceptus as an intra-uterine allograft within the immunologically competent genetically alien female host. Medawar's succinct and stimulating theories have been central throughout the whole of this time and his basic conclusion, that the single most important factor ensuring the success of gestation is the anatomical separation of the fetus from its mother, remains substantially valid to this day. The extent to which other factors are of significance, particularly those relating to the relative roles of maternal adaptive and innate immune responses to the developing feto-placental unit, has yet to be fully defined.

Maternal B Lymphocytes Specific for Paternal Histocompatibility Antigens Are Partially Deleted During Pregnancy

Although genetically different from its mother, a mammalian fetus bearing paternal alloantigens is normally not rejected. To investigate one of the many possible mechanisms involved in this important biologic phenomenon, we analyzed the consequences of fetal alloantigen recognition on maternal B lymphocytes. We used transgenic mice expressing a unique B cell receptor with a relatively high affinity for the MHC class I molecule H-2Kk on most B lymphocytes. We provide the first evidence for an alloantigen-specific B cell deletion in the spleens and bone marrow of transgenic mothers bearing H-2Kk-positive fetuses. This highly reproducible deletion affects ≤80% of Id-bearing B cells, starts at midpregnancy, and is only observed until term. Such a specific maternal B cell deletion could contribute to the success of the fetal allograft.

Expression of allogeneic MHC class I antigens by transgenic mouse trophoblast does not interfere with the normal course of pregnancy

Mammalian embryos express paternal histocompatibility antigens which make them potential targets for maternal immune responses. Yet, the histoincompatible fetus survives and develops normally. Down regulation of classical MHC antigen expression by trophoblast cells which are in direct contact with maternal circulation has been repeatedly shown. The trophoblast cells are unable to function properly in antigen presentation and do not induce allogeneic rejection reactions. In the present study we have created transgenic mice that express an allogeneic class I transgene whose transcription is controlled by the transferrin receptor promoter. The expression patterns of the transgene product mice from a single transgenic line were studied in each of the typical placental subpopulations. The allogeneic class I antigen was expressed in the allantoic plate region of the trophoblast, and this expression was not restricted to the endothelial region but extended also to the spongiotrophoblast, as well as the major blood vessels and in the endodermal sinuses. In contrast to the normal class I expression, prominent levels of allogeneic H-2 antigens were detected in the labyrinthine trophoblast. The fetal resorption rate in females mated with these transgenic males was not higher then the normal rate, and the embryos survived and developed normally. These data imply that the unusual expression of allogeneic class I antigens in certain trophoblast subpopulations does not affect fetal development.

Induction of transient murine T cell anergy by a low molecular weight compound obtained from supernatants of human placental cultures is linked to defective phosphorylation of TCR CD3 chain

PROBLEM

Allopregnancy induces specific transient tolerance to paternal grafts, and we know that a low molecular weight material ("filtrate") present in a human placental supernatant can do so in vitro (specific unresponsiveness) as well as in vivo, such as when preventing graft-versus-host reaction (GVH) produced by A cells injected into irradiated A x B F1s recipient. We also know by studies carried out using specific anti-V beta-specific stimulation as well as secondary and primary mixed lymphocyte reaction in major histocompatibility complex (MHC) only incompatible combinations that the material acts by inducing T cell anergy rather than clonal deletion. We explored the mechanism of such an anergy, which we know was not dependent on calcium fluxes, cyclic adenosine monophosphate (cAMP) levels, or PkC by studies of protein phosphorylation. Having observed in previous studies that expression of T cell reactivity (TcR) in anergic cells was enhanced, but that the numbers of cells expressing a given reactivity (TcR) V beta after specific stimulation in the presence of a filtrate was much higher than it should be, we monitored the receptor expression by fluorescence-activated cell sorter (FACS).

METHOD OF STUDY

We used short-term stimulation of the T-cell-derived Jurkat E6-1 cells by anti-CD3 monoclonal antibody (mAb) or phorbol myristite acetate plus calcium ionophore in the presence or absence of human placental low molecular weight suppressor factors, followed by Western blotting. Transfer on nitrocellulose filters so as to allow the revelation of the phosphorylations was realized by means of a specific antiphosphotyrosin mAb. The final revelation was obtained by chemiluminescence. Similar experiments were performed on anti-V beta-stimulated BALB/c splenocytes, as well as cyproflaxin-treated cells, which are hyper-responsive in cell proliferation assays in the presence of the filtrate. In parallel, cells that were stimulated by a specific anti-V beta and were rendered specifically anergic were studied by a specific anti-V beta and were rendered specifically anergic were studied for other TcR expression using an FACS and both fluorescein isothiocyanate (FITC) and phycoerythrin (PE)-labelled, related and unrelated anti-V beta mAbs.

RESULTS

The phosphorylation of the zeta chain homodimer quantitatively defective in filtrate-treated, anti-V beta 6-stimulated splenocytes as well as in Jurkatt cells. In parallel, cells from cyproflaxin-treated Jurkatt cells were showing enhanced phosphorylation of all bands. The labelling of filtrate-treated anti-V beta 6-stimulated cells by an unrelated anti-V beta (anti-V beta 8) showed double expression of V beta chains. The percentage of cells expressing this unrelated V beta (V beta 8) was normal.

CONCLUSIONS

T cell anergy induced by a filtrate is linked to defective phosphorylation of the zeta-chain homodimer. The abnormal percentage of the cells expressing TcR after filtrate treatment might be due to adsorption by unstimulated cells of soluble TcR V beta-chain, possibly as a result of excess synthesis followed by membrane protease cleavage, allowing release in a soluble form of TcR V beta-chain nonspecifically captured by other cells.

Expression of an immunomodulatory protein known as progesterone induced blocking factor (PIBF) does not correlate with first trimester spontaneous abortions in progesterone supplemented women

PROBLEM

An immunomodulatory protein known as the progesterone induced blocking factor (PIBF) has been found to positively correlate with early pregnancy beta human chorionic gonadotropin (B-hCG) levels. The study presented herein evaluated PIBF levels from conception to the end of the first trimester to determine if lower levels will correlate with first trimester spontaneous abortions (SAB).

METHOD

Progesterone induced blocking factor expression by lymphocytes measured using an immunocytochemistry method was compared in pregnant women with ongoing vs. failed pregnancies.

RESULTS

There were no differences in the proportion of women having lymphocytes expressing PIBF or in the median numbers when comparing ongoing vs. failed pregnancies. There was no B-hCG interval where failed pregnancies were found to have lower frequency of PIBF expressing lymphocytes.

CONCLUSION

Inadequate PIBF expression independent of low P levels does not appear to be an etiologic factor for first trimester SABs; thus measuring this protein in pregnant women lacks practical usefulness.

Further evaluation of the pregnancy-linked down-regulation of the paternal antigen-specific splenic cytotoxic T lymphocyte activity in allogeneically pregnant mice

Cytotoxic T lymphocyte (CTL) activity directed against paternal alloantigen was examined in allogeneically pregnant mice using various allogeneic combinations. The spleen cells from pregnant C57BL/6 (H-2b) mice mated with BALB/c (H-2d) male mice generated less anti-H-2d CTL after in vitro sensitization than those from unpregnant or syngeneically mated C57BL/6 mice. Different allogeneic combinations including the incompatibility at only D region of H-2 or minor histocompatibility loci were effective for downregulating the anti-paternal CTL activity in pregnancy. The downregulation of anti-paternal CTL activity induced by allogeneic pregnancy occurred at day 10 to day 18 of pregnancy, most extensively at day 14. The allogeneic pregnancy also downregulated the allogeneic CTL activities that had been amplified by injecting alloantigens before mating.

In vitro and in vivo immunosuppressive effects of supernatants from human choriocarcinoma cell lines

Local immunosuppression mediated by placental suppressor factors may contribute to the absence of consistently demonstrable cellular immunity against the fetus. In this context, we have investigated the immunosuppressive capabilities of supernatants from human trophoblastic choriocarcinoma cell lines (HCS) by testing the effects of HCS on immune responses in vitro and in vivo in the human and murine systems. HCS suppresses mitogen-induced proliferation and mixed lymphocyte reactions in humans and in mice, as well as antigen-induced T cell proliferation in mice. HCS also suppresses the in vivo response of mice to allogeneic cells. Furthermore, HCS when injected intraperitoneally causes the induction of suppressor cells in mice which in turn prevent the mounting of an allogeneic response in other strains of mice. These results indicate that human choriocarcinoma cell lines secrete a suppressor factor(s) which induces suppression in vitro as well as in vivo through the generation of suppressor cells.

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.

Lymphokine production during term human pregnancy: differences between peripheral leukocytes and decidual cells

Although the fetus is considered to be an "allograft" there is little information concerning the role of lymphokines in human pregnancy. Lymphokines are polypeptides secreted by stimulated lymphocytes that direct the immune response by enabling immune effector cells to communicate with each other. To characterize lymphokine production during normal human pregnancy, we isolated peripheral leukocytes and decidual lymphocyte-like cells from women undergoing repeat cesarean section at term. After stimulation with mitogen and paternal antigen for 24 hours, culture supernatants were assayed for granulocyte-macrophage colony-stimulating factor and interleukin-2 by enzyme-linked immunosorbent assay. There was no difference in the amount of interleukin-2 produced by stimulated peripheral and decidual cells. However, granulocyte-macrophage colony-stimulating factor production by stimulated decidual lymphocyte-like cells was significantly greater than granulocyte-macrophage colony-stimulating factor produced by peripheral lymphocytes. Decidual lymphocyte-like cells produced granulocyte-macrophage colony-stimulating factor both spontaneously and after stimulation with mitogen or paternal antigen, whereas peripheral leukocytes did not. This suggests that the decidua constitutes a distinct immunologic microenvironment.

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.

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.

Suppression of T-lymphocyte blastogenesis by ovine trophoblast protein-1 and human interferon-alpha may be independent of interleukin-2 production

Cells derived from the trophoblast tissue of a day 15 sheep conceptus released substances that inhibit incorporation of [3H]thymidine into phytohemagglutinin (PHA)-stimulated ovine lymphocytes. This effect was partially reversed by addition of antiserum to ovine trophoblast protein-1 (oTP-1), a major secretory product of day 13-21 sheep conceptuses and a protein structurally and functionally related to alpha-interferons (IFN-alpha). Human IFN-alpha, unlike dexamethasone, inhibits phytohemagglutinin-induced lymphocyte blastogenesis without reducing interleukin-2 (IL-2) production by the cultures, and conditioned medium containing IL-2 does not promote [3H]thymidine incorporation into ovine lymphocytes when oTP-1 is present. Thus, oTP-1, by virtue of being an IFN, may have a local immunomodulatory role by selectively inhibiting the proliferative responses of certain maternal immune cells to IL-2.

Immunoactive products of human placenta. I. An immunoregulatory factor obtained from explant cultures of human placenta inhibits CTL generation and cytotoxic effector activity

Supernatants were prepared from short-duration explant cultures of term human placentas obtained after cesarean delivery. These supernatants inhibited murine and human mixed lymphocyte reactions, as well as CTL generation. The effects were reversed by an excess of IL-2-containing medium. Similarly, the material inhibited human natural killer cytotoxicity against K 562 targets. The material was subjected to gel-filtration chromatography on an ACA 44 or Bio-Gel A15m column. The apparent MW of the MLR-CML material was about 60-70 kDa, whereas the NK inhibiting activity was eluted in high-MW components (greater than 200 kDa) as well as in the 50-kDa range. The relevance of this material in local immunoregulation during human pregnancy is discussed.

Membrane fluidity of trophoblast cells and susceptibility to natural cytotoxicity

This study examines the relationship between membrane lipid microviscosity and susceptibility of villous trophoblast to lysis by natural cytotoxic cells. Trophoblast-enriched cell suspensions prepared from term human placentae were treated with cholesteryl hemisuccinate (CHS)--a modulator of membrane lipid microviscosity. CHS-treated cells were more susceptible targets for natural lymphocyte cytotoxicity than were untreated controls. In binding experiments, increased binding of lymphocytes to CHS-treated target cells was found. Preincubation with progesterone prevented membrane rigidification by CHS. Progesterone, cortisol, and estriol restored the impaired resistance of CHS-treated trophoblast cells to lysis. We determined microviscosity and progesterone concentration in villous surface membranes, prepared from placentae from idiopathic spontaneous abortions and normal first-trimester pregnancies. An inverse relationship was found between progesterone content and microviscosity of the membranes. Microviscosity of the membranes from abortion placentae was significantly higher (P less than .01) and progesterone concentration was significantly lower (P less than .001) than those in the membranes of normal first trimester placentae.

Antibodies to trophoblast in normal pregnant and secondary aborting women

Enzyme-linked immunosorbent assays (ELISA) with the use of chorionic villous plasma membranes prepared from first trimester and term placentae were employed to detect antibodies to trophoblast in normal primigravid women. Normal pregnant women were found to produce IgG antibodies to trophoblast. These antibodies could be eluted from first trimester placentae. This antibody response was observed in the first trimester and gradually decreased as pregnancy progressed. IgM antibody responses were observed only in the third trimester. Antibodies in some primigravid women and secondary recurrent aborters showed allotypic reactivity with individual trophoblast membranes. This finding was confirmed by immunoblotting experiments in which antibodies from some normal pregnant women were shown to recognize the same trophoblast antigens as those recognized by antibodies from secondary recurrent spontaneous aborters.

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

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

Characterisation of the humoral immune response during murine pregnancy

Blood samples from female C57BL/10 mice mated with CBA/Ca males were obtained before, during and after both first and second pregnancies. A cellular enzyme-linked immunospecific assay (CELISA) was used to detect maternal antibodies against antigens on paternal splenocytes. Alloantibodies were detected in 48% of mice during or 9 days after a first pregnancy and in 82% of mice by the ninth day after the second pregnancy; these antibodies were first observed on day 10 of the first pregnancy. In two of four active multigravid sera tested, an increase in IgG1 concentration was detected; the level of all other isotypes remained within normal limits. Weak binding of alloantibody to an antigen of approximate molecular weight 44,000 was detected on CBA/Ca splenocytes by immunoblotting sera from multiparous animals. These sera also recognised an antigen of similar molecular weight on H-2b identical 129J splenocytes but not on splenocytes from the maternal strain. These results provide further information on the maternal humoral immune response during murine pregnancy.

Lack of evidence for complement-dependent cytotoxic antibodies to fetal paternally derived antigens in the marsupial Macropus eugenii (tammar wallaby)

A total of 241 serum samples from 145 parous tammar wallabies (Macropus eugenii) were screened for presence of antibodies to paternally derived antigens of the fetus. These samples were taken at different stages in late pregnancy after placental contact was intimate and after birth. Complement-dependent cytotoxicity tests were unable to detect any specific antibodies. It is concluded that the yolk sac placenta of M. eugenii does not allow intimate enough contact between fetal tissues and the maternal circulation to induce formation of cytotoxic antibodies by its mother. This is in contrast to eutherian mammals, in which such production of cytotoxic antibodies occurs frequently as a result of pregnancy. Together with other data it is suggested that the short implantation period in M. eugenii, which is common to all marsupials, has probably not evolved to prevent maternal immune attack upon the conceptus.

Binding of immunoglobulins to the major progesterone-induced proteins secreted by the sheep uterus

We examined the binding of immunoglobulins to the uterine milk proteins, the major progesterone-induced proteins secreted by uterine endometrium of pregnant ewes. Binding was ascertained by measuring binding of 125 I-immunoglobulin to uterine milk proteins that were Western or dot-blotted to nitrocellulose or were coupled to Sepharose. The magnitude of binding was greatest for sheep IgM, intermediate for sheep secretory IgA, low for human secretory and serum IgA, and barely detectable for sheep IgG. Binding of IgA and IgM to uterine milk proteins was time and concentration dependent, saturable, inhibited by high ionic strength buffers, and lost due to enzymatic destruction of the Fc portion of the immunoglobulin molecule. In conclusion, the uterine milk proteins preferentially bind IgA and IgM in a species-dependent manner. Such binding may be related to the role of these proteins in the uterus and may make the uterine milk proteins a useful tool for studying or purifying sheep immunoglobulins.

Suppression of lymphocyte activation by a high-molecular-weight glycoprotein released from preimplantation ovine and porcine conceptuses

A high-molecular-weight (MW greater than 660,000), acidic glycoprotein (HMWGP) was purified from incubation medium of preimplantation, elongating ovine (day 16 and 17) and porcine (day 16) conceptuses. HMWGP was tested for its ability to inhibit [3H-methyl]thymidine incorporation into lymphocytes stimulated by phytohemagglutinin or two-way mixed lymphocyte cultures. Ovine and porcine HMWGP inhibited the incorporation of [3H-methyl]thymidine into lymphocytes in a dose-dependent manner. An approximately 50% inhibition was detected at the lowest dose tested (ovine, 25 micrograms/ml; porcine, 5 micrograms/ml). Complete suppression of thymidine incorporation occurred at the highest doses evaluated (ovine, 200 micrograms/ml; porcine, 40 micrograms/ml). This immunosuppressive effect was not the result of an overall cytotoxic effect on lymphocytes as evaluated by trypan blue exclusion. In conclusion, an ovine and porcine conceptus glycoprotein, HMWGP, has potent in vitro immunosuppressive activity in both phytohemagglutinin and mixed lymphocyte cultures. In vivo, HMWGP may have an immunoregulatory role during early pregnancy in the sheep and pig by providing a local immunosuppressive environment within the uterus to prevent conceptus rejection.

Humoral immune responses in murine pregnancy. V. Relationship to the differential immunogenicity of placental and fetal tissues

The nature of the humoral immune response induced in virgin female mice by injections of F1 placental and fetal tissues has been examined and compared to that induced by immunization with F1 adult spleen cells and by multiple allogeneic pregnancy. In a 'responder' strain mouse, as defined by the ability of multiple allogeneic pregnancy to elicit an anti-paternal humoral immune response, both F1 placental and fetal tissues induced the formation of alloantibodies primarily of the IgG1 sub-class, similar to those induced by allogeneic pregnancy, but different from those elicited by adult spleen cells. However, only the placental tissues induced alloantibodies possessing all the characteristics of those appearing in multiparous allogeneic pregnancy. In contrast, the alloantibodies induced by the injected fetal tissue possessed complement-dependent cytotoxic activity, indicating that the inability of pregnancy-induced alloantibodies to mediate cytotoxicity may not be related to their restriction to the IgG1 sub-class. In a 'non-responder' mouse strain, where multiple allogeneic pregnancy does not lead to a maternal alloantibody response, F1 placental tissues, in contrast to fetal and adult tissues, failed to induce a humoral immune response. Injection of F1 placental tissue therefore elicits responses that mimic both the properties and the strain-dependent distribution of the alloantibodies identified in normal murine pregnancy. This implies that the immunogenic stimulus in pregnancy emanates from the placental rather than the fetal compartment of the allogeneic conceptus.

The rat placenta expresses paternal class I major histocompatibility antigens

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

Collagen-induced arthritis and pregnancy in mice: the effects of pregnancy on collagen-induced arthritis and the high incidence of infertility in arthritic female mice

Collagen-induced arthritis (CIA) in mice is a model of inflammatory polyarthritis that has many features similar to human rheumatoid arthritis. In rheumatoid arthritis, pregnancy leads to amelioration of the disease while exacerbation develops after delivery. We used the CIA model to elucidate the role of pregnancy on disease and vice versa. The onset of arthritis in pregnant mice was delayed in the B10.RIII strains immunized with native porcine type II collagen 7-12 days prior to syngeneic [B10.RIII (susceptible to CIA) X B10.RIII] and allogeneic (B10.RIII female X B10.K male that are CIA resistant) pregnancy. In contrast, when mice were immunized on days 1-6 of pregnancy, the onset of arthritis was earlier as compared with controls. In addition, once the mice developed CIA after delivery, the disease showed markedly rapid progression as compared to the control immunized group. Humoral immune responses to type II collagen showed significantly decreased levels on day 14 (at late stage of pregnancy) both in syngeneic and allogeneic postmating immunized pregnant mice. The same effect was also seen in allogeneic premating immunized pregnant mice on day 21 (at mid-stage of pregnancy). The levels of these antibodies increased after delivery. Subclasses of IgG1 and IgG2a antibodies to type II collagen were suppressed during pregnancy. In the pseudopregnant group, these antibodies showed decreased levels on day 14, but did not differ from the control groups on day 21 and 28. Some immunoregulatory changes may play a role in these alterations in pregnant arthritic mice. In comparison to the effects of syngeneic (susceptible X susceptible) pregnancy on CIA, allogeneic (susceptible female X resistant male) pregnancy seemed to be beneficial for the affected individuals. Litter size and mean birth weight were not affected by immunization of type II collagen. After onset of CIA, both syngeneic and allogeneic matings failed to produce offspring in arthritic female mice. The estrus cyclicity was highly disturbed in arthritic female mice and gonadotropin stimulation in arthritic mice induced significantly less ova in oviducts and maturing follicles as compared to nonarthritic controls. Immunological factors yet to be elucidated may be involved in this ovarian dysfunction.

Immune reactivity of allogeneically pregnant mice to paternal MHC antigens on fetal and placental cells assessed by second set rejection of ascites tumor cells

In vivo immunogenicity of fetus- and placenta-derived cells as well as the immune reactivity of pregnant mice to fetal cells were examined for graft rejecting response (GRR). Systemic administration of small numbers of fetal cells but not placental cells from allogeneically pregnant mice (10(6) cells per mouse) or adult allogeneic spleen cells (10(4) cells) sensitized mice for second-set rejection of an ascitic tumor bearing paternal major histocompatibility complex (MHC) antigens. Despite this fact and the known positive humoral response, pregnant and parous mice are not even minimally sensitized with fetal MHC antigens for GRR transplacentally. Nevertheless, any pregnancy-related systemically active control, which would selectively prevent the mother from being sensitized for GRR by limiting numbers of semi-allogeneic fetal cells, was not demonstrable in either allogeneically or syngeneically pregnant mice. Irrespective of pregnancy, mice did not, however, respond to repeated administration of very small numbers of allogeneic spleen cells (5 X 10(2) cells per mouse) for graft rejection. These findings support the notion that deviation of maternal immunity to fetal antigens away from harmful GRR is mediated principally by local mechanisms which inhibit fetal cells from gaining access to the mother for GRR, and additionally by the innate inability of mice to respond to very small numbers of allogeneic cells that might escape past the local maternal-fetal barrier.

A monoclonal antibody, EC-1, derived from a syngeneically multiparous mouse alters in vitro fertilization and development

A monoclonal antibody designated 'EC-1' was derived from a fusion of myeloma cells with lymphoid tissue from a syngeneically multiparous, but otherwise unimmunized, mouse and was selected by screening for reactivity with teratocarcinoma cells. The IgM antibody binds to the cell surface of ova, zygotes, and 2-cell embryos. Binding is not detected on the 4- or 8-cell embryo but reappears on the morula and blastocyst. EC-1 binds to the trophoblast but not to the inner cell mass of in vitro attached blastocysts and the ectoplacental cone of the peri-implantation embryo. In adult tissues, EC-1 binds to the follicular cells of the ovary, the lining epithelium of the pregnant uterus, the interstitial region of the testes and to epididymal but not testicular sperm. In nongonadal tissues EC-1 binds to an epitope located in some, but not all, regions of connective tissues associated with basement membrane. The antigen detected by EC-1, as expressed on teratocarcinoma-derived cell line PYS-2, is a large glycoprotein which is sensitive to reduction. EC-1 inhibits in vitro fertilization and partially inhibits in vitro development of in vitro fertilized ova. The possible implications of EC-1 binding and activity are discussed.

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.

The effect of parental HLA compatibility on the expression of paternal haplotypes in offspring

The compatibility of HLA-A,-B expression between mother and offspring was examined in 410 families serologically tissue typed within a single transplant lab from 1972 thru 1982. The study group included 410 mothers of 1719 children (range 2-13/mother), with 352 one-father and 58 multiple-father families There were seven cases of monozygous twins and seven cases each of maternal and paternal allelic recombination. The degree of haplotype matching between the oldest offspring and subsequent siblings was within the expected range of distribution. The number of maternal HLA-A,-B antigens matched or mismatched with paternal antigens of the offspring did not show a significant difference between early born or late born siblings either in one-father or multiple-father families. In addition, where the mother showed significant sensitization to paternal HLA-A,-B antigens ther was no apparent selection against the incompatible paternal HLA antigens or associated haplotypes in subsequent offspring. These data suggest that maternal HLA compatibility with the father is not a significant selective factor in determining the expression of paternal haplotypes in offspring.

Systemic active suppression is not necessary for successful allopregnancy

To investigate the role of systemic suppression during allopregnancy, CBA/J female mice were immunised against H-2d prior to mating. Cytotoxic T lymphocyte (CTL) activity was tested at days 14-16 of pregnancy. A reduction of CTL activity was observed only in multiparous animals. Although a nonspecific suppression was detected in isopregnancy, suppression was more marked in allopregnancy. Conversely, the CTL activity observed in the spleen during the first pregnancy (iso or allo) was always significant in mice presensitized with 2 or 3 alloimmunizations prior to pregnancy. Such animals have in vivo effector cells, since allografts of Sarcoma Sa1 were rejected in secondary fashion in alloimmunized mice, while the fetus remained unharmed. These observations demonstrate that allospecific anti-MHC CTLs are specifically impaired in multiple allopregnancy, but also tend to rule out theories postulating that systemic suppression of CTL generation and function is required for successful allopregnancy.

Humoral immune responses in murine pregnancy. IV. Strain dependency and alloantibody specificity

The relationship between the ability of female inbred mice to produce an anti-paternal humoral immune response to allogeneic multiparity and the genotype of the female and male strains has been investigated. Only three, all H-2b haplotype strains, were 'responder' strains and produced anti-paternal alloantibody which did not exhibit C'-dependent cytotoxicity. 'Non-responder' strains produced no alloantibody in spite of multiple pregnancies with H-2 and non-H-2 incompatible male strains. However, even responder strains did not produce alloantibody with all incompatible male strains. The absence of a response in a responder strain mated with a male strain differing at only the H-2 locus implicated a role for non-H-2 influences. A study of the specificity of pregnancy-induced alloantibody suggested that this represented only a fraction of the total alloantibody population induced by conventional immunization in the same strain combination. It is suggested that in pregnancy only the anti-non-H-2 humoral responses remain similar to those induced by immunization, whereas anti-H-2 humoral responses are either absent or are restricted to a fraction of the total foreign H-2 specificities presented. These observations are discussed in relation to the nature of the immunogenic stimulus in pregnancy and the expression of histocompatibility antigens on the feto-placental unit.

Immunoglobulin-secreting cells in various maternal lymphoid tissues during syngeneic and allogeneic murine pregnancy

The effects of syngeneic (CBAxCBA) and allogeneic (CBAxC57/B1) pregnancy on immunoglobulin (Ig)-secreting cells in various maternal organs/tissues have been investigated by using the protein A plaque assay. The following organs/tissues were examined: a) spleen, b) cervical nodes, c) inguinal nodes, d) mesenteric nodes, e) para-aortic (uterus-draining) nodes, f) Peyer's patches, and g) bone marrow (femur). The changes observed were similar and of the same magnitude in all pregnant animals, irrespective of the type of mating. At mid-gestation (day 14) a distinct increase in Ig secretors was observed, predominantly in the spleen. At the end of pregnancy (day 20) the para-aortic nodes contained dramatically increased numbers of plaque forming cells. A slight increase in both IgM and IgG-secreting cells was also seen in bone marrow at the very end of pregnancy, while Peyer's patches and the nodes of neck and legs appeared to be unaffected throughout the period of gestation.