Programmed cell death-1 (PD-1) and T-cell immunoglobulin mucin-3 (Tim-3) regulate CD4+ T cells to induce Type 2 helper T cell (Th2) bias at the maternal-fetal interface.

STUDY QUESTION: Are the immune regulatory molecules programmed cell death-1 (PD-1) and T-cell immunoglobulin mucin-3 (Tim-3) involved in regulating CD4+ T cell function during pregnancy? SUMMARY ANSWER: PD-1 and Tim-3 promote Type 2 helper T cell (Th2) bias and pregnancy maintenance by regulating CD4+ T cell function at the maternal-fetal interface. WHAT IS KNOWN ALREADY: The maternal CD4+ T cell response to fetal antigens is thought to be an important component of maternal-fetal tolerance during pregnancy. PD-1 and Tim-3 are important for limiting immunopathology. The co-expression of PD-1 and Tim-3 on T cells identifies a T cell subset with impaired proliferation and cytokine production. Combined blockade of Tim-3 and PD-1 could restore T cell function to the greatest degree. STUDY DESIGN, SIZE, DURATION: The expression of PD-1 and Tim-3 on CD4+ T cells was analyzed by flow cytometry, and in vitro and in vivo analyses were used to investigate the role of PD-1/Tim-3 signal in the regulation of CD4+ T cells function and pregnancy outcome. PARTICIPANTS/ MATERIALS, SETTING, METHODS: A total of 88 normal pregnant women, 37 women with recurrent spontaneous abortion, 36 normal pregnant mice and 45 abortion-prone mice were included. We measure the expression of PD-1 and Tim-3 on CD4+ T cells and their relationship to the function of CD4+ T cells and pregnancy outcome, as well as the effects of blocking PD-1 and Tim-3 pathways on decidual CD4+ T (dCD4+ T) cells during early pregnancy. MAIN RESULTS AND THE ROLE OF CHANCE: PD-1 and Tim-3, by virtue of their up-regulation on dCD4+ T cells during pregnancy, define a specific effector/memory subset of CD4+ T cells and promote Th2 bias at the maternal-fetal interface. Using in vitro and in vivo experiments, we also found that combined targeting of PD-1 and Tim-3 pathways results in decreased production of Th2-type cytokines by dCD4+ T cells and increased fetal resorption of normal pregnant murine models. Moreover, decreased PD-1 and Tim-3 on dCD4+ T cells may be associated with miscarriage. LIMITATIONS AND LIMITS OF CAUTION: Further study is required to examine the mechanism of PD-1 and Tim-3 effects on Th2 cytokine production by CD4+ T cells during pregnancy. WIDER IMPLICATIONS OF THE FINDINGS: These results have important implications for understanding the physiological mechanisms that promote maternal-fetal tolerance. Our study also indicates that targeting Tim-3 and PD-1 pathways may represent novel therapeutic strategies to prevent pregnancy loss. STUDY FUNDING/COMPETING INTERESTS: This study was supported by the National Basic Research Program of China (2015CB943300); National Nature Science Foundation of China (81490744, 91542116, 31570920, 81070537, 31171437, 81370770, 31270969, 31570920, 91542116); the Key Project of Shanghai Municipal Education Commission (14ZZ013) and the Key Project of Shanghai Basic Research from Shanghai Municipal Science and Technology Commission (12JC1401600). None of the authors have any conflict of interest to declare.

NKG2D blockade inhibits poly(I:C)-triggered fetal loss in wild type but not in IL-10-/- mice.

Infection and inflammation can disturb immune tolerance at the maternal-fetal interface, resulting in adverse pregnancy outcomes. However, the underlying mechanisms for detrimental immune responses remain ill defined. In this study, we provide evidence for immune programming of fetal loss in response to polyinosinic:polycytidylic acid (polyI:C), a viral mimic and an inducer of inflammatory milieu. IL-10 and uterine NK (uNK) cells expressing the activating receptor NKG2D play a critical role in poly(I:C)-induced fetal demise. In wild type (WT) mice, poly(I:C) treatment induced expansion of NKG2D(+) uNK cells and expression of Rae-1 (an NKG2D ligand) on uterine macrophages and led to fetal resorption. In IL-10(-/-) mice, NKG2D(-) T cells instead became the source of fetal resorption during the same gestation period. Interestingly, both uterine NK and T cells produced TNF-α as the key cytotoxic factor contributing to fetal loss. Treatment of WT mice with poly(I:C) resulted in excessive trophoblast migration into the decidua and increased TUNEL-positive signal. IL-10(-/-) mice supplemented with recombinant IL-10 induced fetal loss through NKG2D(+) uNK cells, similar to the response in WT mice. Blockade of NKG2D in poly(I:C)-treated WT mice led to normal pregnancy outcome. Thus, we demonstrate that pregnancy-disrupting inflammatory events mimicked by poly(I:C) are regulated by IL-10 and depend on the effector function of uterine NKG2D(+) NK cells in WT mice and NKG2D(-) T cells in IL-10 null mice.

Listeria monocytogenes cytoplasmic entry induces fetal wastage by disrupting maternal Foxp3+ regulatory T cell-sustained fetal tolerance.

Although the intracellular bacterium Listeria monocytogenes has an established predilection for disseminated infection during pregnancy that often results in spontaneous abortion or stillbirth, the specific host-pathogen interaction that dictates these disastrous complications remain incompletely defined. Herein, we demonstrate systemic maternal Listeria infection during pregnancy fractures fetal tolerance and triggers fetal wastage in a dose-dependent fashion. Listeria was recovered from the majority of concepti after high-dose infection illustrating the potential for in utero invasion. Interestingly with reduced inocula, fetal wastage occurred without direct placental or fetal invasion, and instead paralleled reductions in maternal Foxp3(+) regulatory T cell suppressive potency with reciprocal expansion and activation of maternal fetal-specific effector T cells. Using mutants lacking virulence determinants required for in utero invasion, we establish Listeria cytoplasmic entry is essential for disrupting fetal tolerance that triggers maternal T cell-mediated fetal resorption. Thus, infection-induced reductions in maternal Foxp3(+) regulatory T cell suppression with ensuing disruptions in fetal tolerance play critical roles in pathogenesis of immune-mediated fetal wastage.

Maternal CD4⁺ and CD8⁺ T cell tolerance towards a fetal minor histocompatibility antigen in T cell receptor transgenic mice.

Tolerance of the maternal immune system in pregnancy is important for successful pregnancy because the semiallogeneic fetus may be subject to antifetal responses. We examined maternal tolerance to the fetus using a murine system in which a model paternally inherited antigen, ovalbumin (OVA), is expressed exclusively in the fetus and placenta. By employing T cell receptor (TCR) transgenic mice specific for major histocompatibility complex class I- or class II-restricted epitopes of OVA (OT-I and OT-II) as mothers, we investigated the fate of fetus-specific CD8⁺ and CD4⁺ T cells, respectively, during gestation. Both OVA-specific CD8⁺ and CD4⁺ T cells displayed an activated phenotype in the peripheral lymphoid tissues of OVA-bred OT-I and OT-II mice, consistent with their encounter of fetal antigen. Whereas a small percentage of OVA-specific CD4⁺ T cells were deleted in the periphery and thymus of OVA-bred OT-II mice, with evidence of TCR downregulation in the remaining T cells, deletion and TCR downregulation were not observed in OVA-bred OT-I mice. Both CD4⁺ and CD8⁺ T cells upregulated inducible costimulator expression in response to the fetal antigen, but only CD4⁺ T cells consistently upregulated the inhibitory receptors programmed cell death 1 and cytotoxic T lymphocyte antigen-4. More regulatory T cells (Tregs) were present in pregnant OVA-bred than in WT-bred OT-II mice, revealing that Tregs expanded specifically in response to the fetal antigen. These data indicate that several mechanisms tolerize fetal antigen-specific maternal CD4⁺ T cells, whereas tolerance of fetal antigen-specific CD8⁺ T cells is less effective. The importance of these mechanisms is underscored by the finding that fetal loss occurs in OVA-bred OT-I but not OT-II mice.

Vaccine model of antiphospholipid syndrome induced by tetanus vaccine.

Successful induction of antiphospholipid syndrome (APS) in two different non-autoimmune prone mouse strains, BALB/c and C57BL/6, was achieved by tetanus toxoid (TTd) hyperimmunization using different adjuvants (glycerol or aluminium hydroxide), and different adjuvant pretreatments (glycerol or Complete Freund's Adjuvant (CFA)). APS had different manifestations of reproductive pathology in BALB/c and C57BL/6 mice: fetal resorption (as a consequence of extreme T-cell activation obtained in the course of pretreatment), and lowering of fecundity (as a consequence of polyclonal B-cell stimulation), respectively. In BALB/c mice fetal resorption coincided with glycerol and CFA pretreatments, while in C57BL/6 mice lowering of fecundity was most obvious in CFA-pretreated mice immunized with TTd in aluminium hydroxide. Both molecular mimicry and polyclonal B-cell activation occur in APS induction, with molecular mimicry effects being dominant in BALB/c mice, and polyclonal cell activation being dominant in C57BL/6 mice. Confirmation of molecular mimicry effects, which in the condition of T-cell stimulation generated fetal resorptions in the BALB/c strain, was achieved by passive infusion of monoclonal antibody (MoAb) T-26 specific for TTd and anti-ß(2)-glycoprotein I obtained after TTd hyperimunization. High polyclonal B-cell activation in C57BL/6 mice prevented fetal resorption but induced fecundity lowering, as was the case in passive administration of MoAb T-26 in this mouse strain. Passive infusion of anti-idiotypic MoAb Y7 into C57BL/6 mice induced fetal resorptions and confirmed the above suggestion on the protective role of polyclonal B-cell stimulation in fetal resorptions.

A critical role for the programmed death ligand 1 in fetomaternal tolerance.

Fetal survival during gestation implies that tolerance mechanisms suppress the maternal immune response to paternally inherited alloantigens. Here we show that the inhibitory T cell costimulatory molecule, programmed death ligand 1 (PDL1), has an important role in conferring fetomaternal tolerance in an allogeneic pregnancy model. Blockade of PDL1 signaling during murine pregnancy resulted in increased rejection rates of allogeneic concepti but not syngeneic concepti. Fetal rejection was T cell- but not B cell-dependent because PDL1-specific antibody treatment caused fetal rejection in B cell-deficient but not in RAG-1-deficient females. Blockade of PDL1 also resulted in a significant increase in the frequency of IFN-gamma-producing lymphocytes in response to alloantigen in an ELISPOT assay and higher IFN-gamma levels in placental homogenates by ELISA. Finally, PDL1-deficient females exhibited decreased allogeneic fetal survival rates as compared with littermate and heterozygote controls and showed evidence of expansion of T helper type 1 immune responses in vivo. These results provide the first evidence that PDL1 is involved in fetomaternal tolerance.

Toll-like receptor-4 null mutation causes fetal loss and fetal growth restriction associated with impaired maternal immune tolerance in mice.

Maternal immune adaptation to accommodate pregnancy depends on sufficient availability of regulatory T (Treg) cells to enable embryo implantation. Toll-like receptor 4 is implicated as a key upstream driver of a controlled inflammatory response, elicited by signals in male partner seminal fluid, to initiate expansion of the maternal Treg cell pool after mating. Here, we report that mice with null mutation in Tlr4 (Tlr4-/-) exhibit impaired reproductive outcomes after allogeneic mating, with reduced pregnancy rate, elevated mid-gestation fetal loss, and fetal growth restriction, compared to Tlr4+/+ wild-type controls. To investigate the effects of TLR4 deficiency on early events of maternal immune adaptation, TLR4-regulated cytokines and immune regulatory microRNAs were measured in the uterus at 8 h post-mating by qPCR, and Treg cells in uterus-draining lymph nodes were evaluated by flow cytometry on day 3.5 post-coitum. Ptgs2 encoding prostaglandin-endoperoxide synthase 2, cytokines Csf2, Il6, Lif, and Tnf, chemokines Ccl2, Cxcl1, Cxcl2, and Cxcl10, and microRNAs miR-155, miR-146a, and miR-223 were induced by mating in wild-type mice, but not, or to a lesser extent, in Tlr4-/- mice. CD4+ T cells were expanded after mating in Tlr4+/+ but not Tlr4-/- mice, with failure to expand peripheral CD25+FOXP3+ NRP1- or thymic CD25+FOXP3+ NRP1+ Treg cell populations, and fewer Treg cells expressed Ki67 proliferation marker and suppressive function marker CTLA4. We conclude that TLR4 is an essential mediator of the inflammation-like response in the pre-implantation uterus that induces generation of Treg cells to support robust pregnancy tolerance and ensure optimal fetal growth and survival.

Adoptive-transfer effects of intravenous immunoglobulin in autoimmunity.

Intravenous immunoglobulin (IVIG) is an effective treatment for a variety of autoimmune and inflammatory conditions. The mechanism of action of IVIG remains poorly understood, but a variety of theories have been suggested. Recent studies in murine models have indicated that some of the ameliorative effects of IVIG in autoimmunity can be repeated by the adoptive transfer of leukocytes that have been primed with IVIG. The active cell component within the leukocyte cell population in immune thrombocytopenia (ITP) was determined to be CD11c(+) dendritic cells. This review will highlight recent work in murine systems that indicates that the effects of IVIG can be adoptively transferred in some autoimmune diseases and inflammatory states.

PDL1 blockage increases fetal resorption and Tfr cells but does not affect Tfh/Tfr ratio and B-cell maturation during allogeneic pregnancy.

A successful pregnancy requires sophisticated regulation of uterine microenvironment to guarantee the existence of semi-allogeneic conceptus without immune rejection. T follicular regulatory (Tfr) cells exert a suppressive effect on Tfh-cell expansion, B-cell response, and antibody production. Although accumulating evidence has demonstrated that dysregulations of Tfr cells can bring on various immunological diseases, their immunomodulatory roles during pregnancy still remain unheeded. Herein, we introduced an allogeneic normal-pregnant mouse model and found that CD4+CXCR5hiPD-1hiFoxp3+ Tfr cells were preferentially accumulated in the uterus at mid-gestation and displayed a distinct phenotype. In addition, the absence of PDL1 resulted in increased fetal resorption by favoring Tfr cells accumulation and upregulating PD-1 expression on these cells. However, PDL1 blockade affected neither the ratio of Tfh/Tfr cells nor the maturation and differentiation of B cells. Overall, our results are the first to present a correlation of Tfr cells accumulation with healthy allogeneic pregnancy and PDL1 blockade-induced miscarriage, and to indicate that appropriate assembly of Tfr cells is important for pregnancy maintenance. Since blockade of PD-1-PDL1 pathway leads to more Tfr cells and fetal losses, the reproductive safety must be taken into consideration when PD-1/PD-L1 checkpoint blockade immunotherapy is used in pregnancy.

Pregnancy suppression by active immunization against gestation-specific riboflavin carrier protein.

A riboflavin carrier protein isolated from chickens cross-reacts with a gestation-specific rodent carrier for riboflavin. Active immunization of female rats of proved fertility with the purified chicken carrier protein completely yet reversibly suppressed early pregnancy without impairing implantation per se. Concurrently there were no discernible adverse effects on maternal health in terms of weight gain, vitamin status, and fertility.

IFITM proteins inhibit placental syncytiotrophoblast formation and promote fetal demise.

Elevated levels of type I interferon (IFN) during pregnancy are associated with intrauterine growth retardation, preterm birth, and fetal demise through mechanisms that are not well understood. A critical step of placental development is the fusion of trophoblast cells into a multinucleated syncytiotrophoblast (ST) layer. Fusion is mediated by syncytins, proteins deriving from ancestral endogenous retroviral envelopes. Using cultures of human trophoblasts or mouse cells, we show that IFN-induced transmembrane proteins (IFITMs), a family of restriction factors blocking the entry step of many viruses, impair ST formation and inhibit syncytin-mediated fusion. Moreover, the IFN inducer polyinosinic:polycytidylic acid promotes fetal resorption and placental abnormalities in wild-type but not in Ifitm-deleted mice. Thus, excessive levels of IFITMs may mediate the pregnancy complications observed during congenital infections and other IFN-induced pathologies.

Preterm delivery induced by LPS in syngeneically impregnated BALB/c and NOD/SCID mice.

Strategies of lipopolysaccharide (LPS) stimulation with or without previous toll-like receptor 4 (TLR4) blocking were pursued to investigate the mechanism of LPS-induced preterm delivery in syngeneically impregnated BALB/c and non-obese diabetic (NOD)/LtSz-scid/scid (NOD/SCID [severe combined immunodeficiency] for short) mice. The LPS-stimulated mice were killed at the beginning of preterm labor and pooled placentas were collected in each mouse. Cell surface expression of TLR4, CD80, and intracellular TNF-alpha in placenta CD45(+) cell population was determined by flow cytometry. It displayed that preterm delivery could be induced by LPS in BALB/c, while the NOD/SCID seemed to be resistant to LPS induction. TLR4 expression was not changed in either BALB/c or NOD/SCID mice upon LPS-stimulation, but the CD45(+)CD80(+) cell percentage was elevated in both groups. The CD45(+)TNF-alpha(+) cell percentage was increased merely in BALB/c after the stimulation, while no such trend was observed in NOD/SCID mice. In BALB/c, the effect of LPS on CD80 and TNF-alpha expression could be abrogated by previous TLR4 blocking, subsequently prevent LPS-induced preterm delivery. In another design, NK cell blocking was performed at earlier stage of gestation by injections of anti-asialo GM1 antiserum (ASGM1). It appeared that LPS-induced preterm delivery could be partially prevented by this blocking in BALB/c mice. Such data, together with the diversity of sensitivity to LPS induction observed in BALB/c and NOD/SCID mice, imply that LPS interacts with TLR4, triggers the mobilization of CD45(+)CD80(+) cells, results in elevated production of inflammatory cytokines, and finally results in preterm delivery. In addition, NK cells may be involved in the signaling cascade, and the lack of functional NK cells in the NOD/SCID may be why these mice appeared to be less sensitive to LPS-induced premature labor.

Role of Paternal Antigen-Specific Treg Cells in Successful Implantation.

Maternal lymphocytes recognize fetal antigens, so tolerance is necessary to prevent rejection. Seminal plasma is important for induction of paternal antigen-specific Treg cells in the uterine draining lymph nodes and the pregnant uterus. Elimination of Treg cells during implantation or early pregnancy induces implantation failure or fetal resorption in mice. Immunosuppressive therapy with an anti-TNF antibody or the immunosuppressive agent tacrolimus improves the pregnancy rate in women with repeated implantation failure and recurrent pregnancy loss of unknown etiology, suggesting that Treg cells play an essential role in successful implantation and pregnancy in humans.

IL-7/IL-7R signaling pathway might play a role in recurrent pregnancy losses by increasing inflammatory Th17 cells and decreasing Treg cells.

PROBLEM: We aim to investigate a possible role of IL-7/IL-7R signaling pathway in recurrent pregnancy losses (RPL). MATERIAL AND METHODS: Using the abortion-prone (AP) and non-abortion-prone (NP) mice model, fetal resorption rates (FRR), Th17 and Treg cells-related factors, and the effect of IL-7 and IL-7R antagonist were investigated by flow cytometry, quantitative real-time PCR, and immunohistochemistry. IL-7 and IL-7R expressions in human decidua were investigated by immunohistochemistry. RESULTS: In the AP mice, IL-7R antagonist treatment significantly decreased FRR by downregulating Th17 and upregulating Treg-related factors. When the NP mice were treated with IL-7, FRR was significantly increased by upregulating Th17 and downregulating Treg-related factors. In decidual stromal cells of women with RPL, increased IL-7 and decreased IL-7R expressions were present when compared to normal controls. CONCLUSION: IL-7/IL-7R signaling pathway plays a possible role in RPL by upregulating Th17 immunity, meanwhile downregulating Treg immunity. Regulation of IL-7/IL-7R may be a new therapeutic strategy for RPL.

Placental immunopathology and pregnancy failure in the FIV-infected cat.

Placental HIV infections frequently result in infected babies or miscarriage. Aberrant placental cytokine expression during HIV infections may facilitate transplacental viral transmission or pregnancy perturbation. The feline immunodeficiency virus (FIV)-infected cat is a model for HIV infections due to similarities in biology and clinical disease. The purpose of this study was to evaluate placental immunomodulator expression and reproductive outcome using the FIV-infected cat model. Kittens were cesarean delivered from FIV-B-2542-infected and control queens near term; placental and fetal tissues were collected. Real-time RT-PCR was used to measure expression of representative placental Th1 cytokines, interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma), a Th2 cytokine, IL-10, and chemokine receptor CXCR4. On average, control queens delivered 3.8 kittens/litter; 1 of 31 kittens (3.2%) was non-viable. FIV-infected queens produced 2.7 kittens/litter; 15 of 25 concepti (60%) were non-viable. FIV was detected in 14 of 15 placentas (93%) and 21 of 22 fetuses (95%) using PCR. Placental immunomodulator expression did not differ significantly when placentas from infected cats were compared to those of control cats. However, elevated expression of Th1 cytokines and increased Th1/Th2 ratios (IL-1beta/IL-10) occurred in placentas from resorptions. Therefore, increased placental Th1 cytokine expression was associated with pregnancy failure in the FIV-infected cat.

CXCR3 blockade protects against Listeria monocytogenes infection-induced fetal wastage.

Mammalian pregnancy requires protection against immunological rejection of the developing fetus bearing discordant paternal antigens. Immune evasion in this developmental context entails silenced expression of chemoattractant proteins (chemokines), thereby preventing harmful immune cells from penetrating the maternal-fetal interface. Here, we demonstrate that fetal wastage triggered by prenatal Listeria monocytogenes infection is driven by placental recruitment of CXCL9-producing inflammatory neutrophils and macrophages that promote infiltration of fetal-specific T cells into the decidua. Maternal CD8+ T cells with fetal specificity upregulated expression of the chemokine receptor CXCR3 and, together with neutrophils and macrophages, were essential for L. monocytogenes-induced fetal resorption. Conversely, decidual accumulation of maternal T cells with fetal specificity and fetal wastage were extinguished by CXCR3 blockade or in CXCR3-deficient mice. Remarkably, protection against fetal wastage and in utero L. monocytogenes invasion was maintained even when CXCR3 neutralization was initiated after infection, and this protective effect extended to fetal resorption triggered by partial ablation of immune-suppressive maternal Tregs, which expand during pregnancy to sustain fetal tolerance. Together, our results indicate that functionally overriding chemokine silencing at the maternal-fetal interface promotes the pathogenesis of prenatal infection and suggest that therapeutically reinforcing this pathway represents a universal approach for mitigating immune-mediated pregnancy complications.

Effects of antiprogesterone antiserum on serum and ovarian progesterone, gonadotropin secretion, and pregnancy in the rat.

A high affinity antiprogesterone antibody (APA) was tested in both pseudopregnant and pregnant rats for its ability to alter serum and ovarian concentrations of total and free progesterone and serum gonadotropins and for contragestational effects. APA injected ip on the sixth day of pseudopregnancy resulted in rapidly increased levels of total progesterone in serum, but no detectable change in free progesterone as measured by equilibrium dialysis. Serum gonadotropins similarly increased after APA injection. Progesterone concentrations in various body tissues indicated an initial increase in progesterone production followed by a marked decrease apparently in response to induce luteolysis. Similar levels of hormones were obtained in pregnant rats after ip administration of APA on day 10 of gestation. Fetal resorption followed in all animals and was complete within 96 h. The effect of APA on fetal loss appears to be a combination of a direct reduction of uteroovarian progesterone concentration and a negative feedback of progesterone on the pituitary release of gonadotropins, thus resulting in luteolysis and a further reduction in available progesterone.

Allopregnancy in B-cell deprived C57/BL mice--an investigation focusing on the relationship between survival of the fetuses and anti-paternal immune activity of the mothers.

C57/B1 female mice (haplotype H2-b) were treated throughout their life cycles with rabbit anti-mouse IgM antibodies in order to remove all maturing B-lymphocytes. At an age of 40 days the B-cell-deprived mice and the corresponding controls were allowed to mate with CBA/Ca males (haplotype H2-k). Four groups of allopregnant animals were investigated: (A) mice not subjected to further treatment, which were allowed to pass through a first pregnancy, (B) mice not subjected to further treatment, which were allowed to pass through a first and second pregnancy, (C) mice immunized with paternal cells prior to mating and then allowed to pass through a first pregnancy, (D) mice which during their first pregnancy were given transfusions of anti-paternal lymphocytes obtained from hyperimmune virgin donors. All animals were dissected on the calculated day for parturition (or the first day that abortions or resorptions were detected). On conclusion of the experiments, the efficiency of the anti-IgM treatment was defined for each mouse, using three different methods (ELISA for detection of serum IgG, immune staining for detection of surface Ig-carrying cells, and the protein A plaque assay for detection of Ig-secreting cells). The T-cell function was recorded in vitro by ConA responsiveness. In addition, control animals were assayed for anti-paternal serum antibodies. In experiments (A), (B) and (C), B-cell-deprived mice and corresponding controls were equally successful in passing through pregnancy, having fairly similar litter sizes and resorption frequency. In group (D), however, some of the anti-IgM-treated mice resorbed all her fetuses. Those that gave birth at on schedule had a resorption frequency and litter size fairly similar to those of the controls.

Morphometric analysis of the histology of spontaneous fetal resorption in a murine pregnancy.

Immunopathology of the spontaneous resorption phenomenon in the CBA x DBA/J murine model was explored using morphometric analysis. Accompanying the previously reported presence of natural killer (NK) cells in resorptive feto-placental units we find major changes in tissue morphology indicating that early infiltration of the feto-placental unit by maternal leukocytes plays a direct role with NK cells in fetal demise. Total number of cell nuclei per field and total nuclear area per field were significantly elevated in feto-placental units containing abnormally increased NK cell presence before detectable resorption as early as day 7 of gestation. This difference persisted throughout all stages of early gestation up to and including the final resorption event at day 10 to 12. Increases in cell density were also detected in areas of the embryonic unit not associated with NK infiltration. These results demonstrate that the spontaneous resorption phenomenon in this model involves: (i) Early (day 7-8) cellular infiltration of the decidual-ectoplacental cone junction associated with the presence in this area of NK cells. (ii) Late (day 8-9) cellular infiltration of the ectoplacental cone.

Decidua-associated suppressor activity and viability of individual implantation sites of allopregnant C3H mice.

Release of soluble suppressor activity from individual implant site decidua of DBA/2-mated C3H/HeJ mice was measured on days 12.5-13.5 of pregnancy. Suppressor activity varied among sites and followed a distribution curve that was displaced towards low suppression when resorption sites were compared to healthy embryonic implants. Pre-immunization against the DBA/2 strain paternal antigens failed to increase resorption (by loss of low suppression implants) but led instead to a reduced resorption rate. This was associated with an increase in soluble suppressor activity obtained from decidua. Some reduction in resorption occurred independent of an increase in the level of suppression suggesting additional contributing factors to the immunization effect.