Mareike Tometten

A pivotal role for galectin-1 in fetomaternal tolerance

A successful pregnancy requires synchronized adaptation of maternal immune-endocrine mechanisms to the fetus. Here we show that galectin-1 (Gal-1), an immunoregulatory glycan-binding protein, has a pivotal role in conferring fetomaternal tolerance. Consistently with a marked decrease in Gal-1 expression during failing pregnancies, Gal-1–deficient (Lgals1−/−) mice showed higher rates of fetal loss compared to wild-type mice in allogeneic matings, whereas fetal survival was unaffected in syngeneic matings. Treatment with recombinant Gal-1 prevented fetal loss and restored tolerance through multiple mechanisms, including the induction of tolerogenic dendritic cells, which in turn promoted the expansion of interleukin-10 (IL-10)–secreting regulatory T cells in vivo. Accordingly, Gal-1s protective effects were abrogated in mice depleted of regulatory T cells or deficient in IL-10. In addition, we provide evidence for synergy between Gal-1 and progesterone in the maintenance of pregnancy. Thus, Gal-1 is a pivotal regulator of fetomaternal tolerance that has potential therapeutic implications in threatened pregnancies.

Depletion of CD8+ cells abolishes the pregnancy protective effect of progesterone substitution with dydrogesterone in mice by altering the Th1/Th2 cytokine profile

One of the most remarkable immunological regulations is the maternal immune tolerance toward the fetal semiallograft during pregnancy, which has been referred to as immunity’s pregnant pause. Rejection of the semiallogeneic trophoblast cells must be selectively inhibited and pathways presumably include Th2 cytokines unopposed by Th1 cytokines. Steroid hormones, including progesterone, have similar effects. Low levels of progesterone and Th2 cytokines and high levels of Th1 cytokines are attributable for increased abortions in mammalians, which may be triggered by psychoemotional stress. Thus, the aim of the present study was to provide experimental evidence for the mechanism involved in the mediation of immune responses by endocrine signals during pregnancy and stress-triggered pregnancy failure. DBA/2J-mated CBA/J female mice were randomized in three groups: 1) control females, 2) mice exposed to stress on gestation day 5.5, and 3) mice exposed to stress and substituted with dydrogesterone, a progestogen with a binding profile highly selective for the progesterone receptor on gestation day 5.5. On gestation days 7.5, 9.5, and 10.5, mice of each group were sacrificed, and the frequency of CD8+ cells and cytokine expression (IL-4, IL-12, TNF-α, IFN-γ) in blood and uterus cells was evaluated by flow cytometry. Additionally, some mice were depleted of CD8 cells by injection of mAb. We observed that progesterone substitution abrogated the abortogenic effects of stress exposure by decreasing the frequency of abortogenic cytokines. This pathway was exceedingly CD8-dependent, because depletion of CD8 led to a termination of the pregnancy protective effect of progesterone substitution.

Dendritic Cells: Key to Fetal Tolerance?

Abstract Pregnancy is a unique event in which a fetus, despite being genetically and immunologically different from the mother (a hemi-allograft), develops in the uterus. Successful pregnancy implies avoidance of rejection by the maternal immune system. Fetal and maternal immune cells come into direct contact at the decidua, which is a highly specialized mucous membrane that plays a key role in fetal tolerance. Uterine dendritic cells (DC) within the decidua have been implicated in pregnancy maintenance. DC serve as antigen-presenting cells with the unique ability to induce primary immune responses. Just as lymphocytes comprise different subsets, DC subsets have been identified that differentially control lymphocyte function. DC may also act to induce immunologic tolerance and regulation of T cell-mediated immunity. Current understanding of DC immunobiology within the context of mammalian fetal-maternal tolerance is reviewed and discussed herein.

Lineage, maturity, and phenotype of uterine murine dendritic cells throughout gestation indicate a protective role in maintaining pregnancy.

Abstract Dendritic cells (DCs) are known to play a major role in the induction, maintenance, and regulation of immune responses. Recently, DCs have been described to be present at the feto-maternal interface in human decidua. However, only limited information is available about DC presence, phenotype, and—more importantly—function throughout gestation. Thus, we analyzed local (uterine) and systemic (blood) DCs in a murine model. DBA/2J mated CBA/J females with vaginal plugs were separated and killed on Gestation Days (GDs) 1.5, 3.5, 5.5, 6.5, 7.5, 8.5, 10.5, 13.5, 15.5, or 17.5. Frequency of uterine and blood CD11c+ DC, phenotype (coexpression of CD8α and major histocompatibility complex class II [MHC II] antigens), and presence of intracellular cytokines (interleukins 12 and 10) were determined by flow cytometry. The morphology of DC in the pregnant uterus was evaluated by immunohistochemistry. In uterus, the relative number of CD11c+ cells increased from GD 5.5, reaching a plateau on GD 9.5 until GD 17.5, while a transient peak of systemic CD11c+ cells was found on GD 8.5 and 10.5. The vast majority of uterine DCs were CD8α− and thus, belonged to the myeloid lineage. Interestingly, a significant peak of lymphoid DC was present on GD 1.5 and 5.5. Further, significantly more intracellular interleukin 10 than interleukin 12 was present in CD11c+ cells. Interestingly, mature DCs (MHC II+) were diminished from GD 5.5 to 8.5. Characterization of CD11c+ cell kinetics in uterus and blood reveals variation of phenotype during pregnancy, pointing toward an eminent immunoregulatory role of DCs throughout gestation at the feto-maternal interface.

Intercellular Adhesion Molecule-1/LFA-1 Cross Talk Is a Proximate Mediator Capable of Disrupting Immune Integration and Tolerance Mechanism at the Feto-Maternal Interface in Murine Pregnancies

Our understanding why a woman’s immune system does not reject her histoincompatible fetus is still very limited. Distinct insights into the mechanisms involved in pregnancy maintenance may help us to prevent pregnancy complications, e.g., miscarriages or pre-eclampsia. Immune integration and tolerance at the feto-maternal interface appear to be indispensable for successful pregnancy maintenance. Little is known about the cross talk between ICAM-1, expressed on epithelium, endothelium, and APC, and its ligand, LFA-1, at the feto-maternal interface. However, based on the role of ICAM-1/LFA-1 in allograft acceptance or rejection upon transplantation, adhesion molecules are likely to interfere with successful pregnancy outcome. In this study, we tested the hypothesis that ICAM-1/LFA-1 pathways may be involved in pregnancy rejection in murine models. By blocking ICAM-1/LFA-1-mediated intercellular adhesion events, we show that fetal immune acceptance is restored in challenged pregnancies (e.g., upon exposure to sound stress), and adoptive transfer of LFA-1 cells into pregnant mice induces rejection only in abortion-prone mouse models. ICAM-1/LFA-1 cross talk leads to increased recruitment of proinflammatory cells to the implantation site, promotes dendritic cell maturation in the decidua, and subsequently induces additional local Th1 polarization via mature dendritic cells. Furthermore, our observations clearly point out that mechanisms of fetal tolerance, e.g., indoleamine 2,3-dioxygenase expression, presence of CD4+CD25bright regulatory T cells, and synthesis of asymmetric Abs, are ICAM-1/LFA-1 dependent. Hence, our data shed light on a hierarchical network of immune integration at the feto-maternal interface, in which ICAM-1/LFA-1 cross talk is clearly a proximate mediator capable of disrupting successful pregnancy maintenance.

Interaction between dendritic cells and natural killer cells during pregnancy in mice

A complex regulation of innate and adaptive immune responses at the maternal fetal interface promotes tolerance of trophoblast cells carrying paternally derived antigens. Such regulatory functions involve uterine dendritic cells (uDC) and natural killer (uNK) cells. The existence of a NK and DC “cross talk” has been revealed in various experimental settings; its biological significance ranging from cooperative stimulation to cell lysis. Little is known about the presence or role of NK and DC cross talk at the maternal fetal interface. The present study shows that mouse NK and DC interactions are subject to modulation by trophoblast cells in vitro. This interaction promotes a tolerogenic microenvironment characterized by downregulation of the expression of activation markers on uNK cells and uDC and dominance of Th2 cytokines. NK and DC interactions would also influence uterine cell proliferation and this process would be strongly modulated by trophoblast-derived signals. Indeed; while low proliferation rates were observed upon regular coculture allowing direct contact between uterine cells and trophoblasts, incubation in a transwell culture system markedly increased uterine cell proliferation suggesting that soluble factors are key mediators in the molecular “dialog” between the mother and the conceptus during the establishment of mouse pregnancy. Our data further reveal that the regulatory functions of trophoblast cells associated with tolerance induction are impaired in high abortion murine matings. Interestingly, we observed that secretion of interleukin-12p70 by uDC is dramatically abrogated in the presence of uNK cells. Taken together, our results provide the first evidence that a delicate balance of interactions involving NK cells, DC, and trophoblasts at the mouse maternal fetal interface supports a successful pregnancy outcome.

Nerve Growth Factor Translates Stress Response and Subsequent Murine Abortion via Adhesion Molecule-Dependent Pathways

Abstract Spontaneous abortion is a frequent threat affecting 10%–25% of human pregnancies. Psychosocial stress has been suggested to be attributable for pregnancy losses by challenging the equilibrium of systems mandatory for pregnancy maintenance, including the nervous, endocrine, and immune system. Strong evidence indicates that stress-triggered abortion is mediated by adhesion molecules, i.e., intercellular adhesion molecule 1 (ICAM1) and leukocyte function associated molecule 1, now being referred to as integrin alpha L (ITGAL), which facilitate recruitment of inflammatory cells to the feto-maternal interface. The neurotrophin beta-nerve growth factor (NGFB), which has been shown to be upregulated in response to stress in multiple experimental settings including in the uterine lining (decidua) during pregnancy, increases ICAM1 expression on endothelial cells. Here, we investigated whether and how NGFB neutralization has a preventive effect on stress-triggered abortion in the murine CBA/J × DBA/2J model. We provide experimental evidence that stress exposure upregulates the frequency of abortion and the expression of uterine NGFB. Further, adhesion molecules ICAM1 and selectin platelet (SELP, formerly P-Selectin) and their ligands ITGAL and SELP ligand (SELPL, formerly P selectin glycoprotein ligand 1) respectively increase in murine deciduas in response to stress. Subsequently, decidual cytokines are biased toward a proinflammatory and abortogenic cytokine profile. Additionally, a decrease of pregnancy protective CD8α+ decidual cells is present. Strikingly, all such uterine stress responses are abrogated by NGFB neutralization. Hence, NGFB acts as a proximal mediator in the hierarchical network of immune rejection by mediating an abortogenic environment comprised of classical signs of neurogenic inflammation.

Nerve Growth Factor in Reproductive Biology: Link between the Immune, Endocrine and Nervous System?

Successful pregnancy outcome requires balanced networking of the immune and endocrine system. In addition, numerous sophisticated adaptive mechanisms promote invasion of fetal tissue and facilitate tolerance. This highly sensitive and vulnerable environment may be challenged from either the maternal or the fetal site. In this overview we collect evidence of a functional role of neurotrophins, predominately nerve growth factor (NGF), in pregnancy maintenance. We demonstrate several pathways through which NGF may be involved in maintaining pregnancy and/or--if exaggerated--inducing pregnancy failure. Due to the pleiotropism of NGF, we hypothesize that NGF is mandatory for the success of pregnancy, e.g. via inhibition of paternal MHC II molecule expression on trophoblast cells. This is supported by published evidence on progesterone, the hormone of pregnancy, which maintains local levels of NGF. On the other hand, if levels of NGF are upregulated in response to environmental challenges, e.g. stress, this may result in a threat to pregnancy maintenance due to a skew towards proinflammatory cytokines and increased apoptotic cell death. Hence, we strongly suggest that NGF constitutes a functional link between the nervous, endocrine and immune system translating environmental or endocrine signals during pregnancy into an immunological answer.

Nerve growth factor and its functional receptor TrkA are up-regulated in murine decidual tissue of stress-triggered and substance P-mediated abortion.

Problem:  Stress, elicited by environmental and social conditions, is known to affect the homeostasis of the nervous, endocrine and immune systems. In pregnancy, perceived stress results in a predomination of inflammatory abortion‐associated Th1 cytokines over immunosuppressive, pregnancy‐protective‐associated Th2 cytokines, putatively via neuropeptide substance P (SP). Nerve growth factor (NGF), an important trophic factor for sympathetic neurons, has been implicated in the responsiveness of immune‐competent cells through its functional receptor, tropomyosin receptor kinase (TrkA). Thus, the aim of the present study was to identify a cross‐talk between distinct neurotrophic and immune mediators in pregnancy maintenance.

Balanced levels of nerve growth factor are required for normal pregnancy progression.

Nerve growth factor (NGF), the first identified member of the family of neurotrophins, is thought to play a critical role in the initiation of the decidual response in stress-challenged pregnant mice. However, the contribution of this pathway to physiological events during the establishment and maintenance of pregnancy remains largely elusive. Using NGF depletion and supplementation strategies alternatively, in this study, we demonstrated that a successful pregnancy is sensitive to disturbances in NGF levels in mice. Treatment with NGF further boosted fetal loss rates in the high-abortion rate CBA/J x DBA/2J mouse model by amplifying a local inflammatory response through recruitment of NGF-expressing immune cells, increased decidual innervation with substance P(+) nerve fibres and a Th1 cytokine shift. Similarly, treatment with a NGF-neutralising antibody in BALB/c-mated CBA/J mice, a normal-pregnancy model, also induced abortions associated with increased infiltration of tropomyosin kinase receptor A-expressing NK cells to the decidua. Importantly, in neither of the models, pregnancy loss was associated with defective ovarian function, angiogenesis or placental development. We further demonstrated that spontaneous abortion in humans is associated with up-regulated synthesis and an aberrant distribution of NGF in placental tissue. Thus, a local threshold of NGF expression seems to be necessary to ensure maternal tolerance in healthy pregnancies, but when surpassed may result in fetal rejection due to exacerbated inflammation.