An assessment of mast-cell deficient mice (W/Wv) as a model system to study the role of histamine in implantation and deciduoma formation

Mast cells as protectors of health

Mast cells (MCs), which are well known for their effector functions in T_H2-skewed allergic and also autoimmune inflammation, have become increasingly acknowledged for their role in protection of health. It is now clear that they are also key modulators of immune responses at interface organs, such as the skin or gut. MCs can prime tissues for adequate inflammatory responses and cooperate with dendritic cells in T-cell activation. They also regulate harmful immune responses in trauma and help to successfully orchestrate pregnancy. This review focuses on the beneficial effects of MCs on tissue homeostasis and elimination of toxins or venoms. MCs can enhance pathogen clearance in many bacterial, viral, and parasitic infections, such as through Toll-like receptor 2-triggered degranulation, secretion of antimicrobial cathelicidins, neutrophil recruitment, or provision of extracellular DNA traps. The role of MCs in tumors is more ambiguous; however, encouraging new findings show they can change the tumor microenvironment toward antitumor immunity when adequately triggered. Uterine tissue remodeling by α-chymase (mast cell protease [MCP] 5) is crucial for successful embryo implantation. MCP-4 and the tryptase MCP-6 emerge to be protective in central nervous system trauma by reducing inflammatory damage and excessive scar formation, thereby protecting axon growth. Last but not least, proteases, such as carboxypeptidase A, released by FcεRI-activated MCs detoxify an increasing number of venoms and endogenous toxins. A better understanding of the plasticity of MCs will help improve these advantageous effects and hint at ways to cut down detrimental MC actions.

Endocrine factors modulating immune responses in pregnancy

How the semi-allogeneic fetus is tolerated by the maternal immune system remains a fascinating phenomenon. Despite extensive research activity in this field, the mechanisms underlying fetal tolerance are still not well understood. However, there are growing evidences that immune–immune interactions as well as immune–endocrine interactions build up a complex network of immune regulation that ensures fetal survival within the maternal uterus. In the present review, we aim to summarize emerging research data from our and other laboratories on immune modulating properties of pregnancy hormones with a special focus on progesterone, estradiol, and human chorionic gonadotropin. These pregnancy hormones are critically involved in the successful establishment, maintenance, and termination of pregnancy. They suppress detrimental maternal alloresponses while promoting tolerance pathways. This includes the reduction of the antigen-presenting capacity of dendritic cells (DCs), monocytes, and macrophages as well as the blockage of natural killer cells, T and B cells. Pregnancy hormones also support the proliferation of pregnancy supporting uterine killer cells, retain tolerogenic DCs, and efficiently induce regulatory T (Treg) cells. Furthermore, they are involved in the recruitment of mast cells and Treg cells into the fetal–maternal interface contributing to a local accumulation of pregnancy-protective cells. These findings highlight the importance of endocrine factors for the tolerance induction during pregnancy and encourage further research in the field.

Estradiol and progesterone regulate the migration of mast cells from the periphery to the uterus and induce their maturation and degranulation

BACKGROUND

Mast cells (MCs) have long been suspected as important players for implantation based on the fact that their degranulation causes the release of pivotal factors, e.g., histamine, MMPs, tryptase and VEGF, which are known to be involved in the attachment and posterior invasion of the embryo into the uterus. Moreover, MC degranulation correlates with angiogenesis during pregnancy. The number of MCs in the uterus has been shown to fluctuate during menstrual cycle in human and estrus cycle in rat and mouse indicating a hormonal influence on their recruitment from the periphery to the uterus. However, the mechanisms behind MC migration to the uterus are still unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We first utilized migration assays to show that MCs are able to migrate to the uterus and to the fetal-maternal interface upon up-regulation of the expression of chemokine receptors by hormonal changes. By using a model of ovariectomized animals, we provide clear evidences that also in vivo, estradiol and progesterone attract MC to the uterus and further provoke their maturation and degranulation.

CONCLUSION/SIGNIFICANCE

We propose that estradiol and progesterone modulate the migration of MCs from the periphery to the uterus and their degranulation, which may prepare the uterus for implantation.

Histamine regulates placental cytokine expression--in vivo study on HDC knockout mice

Successful pregnancy is closely related to polarization toward a Th2 type immune response. As histamine is known to initiate Th2 dominance during inflammatory processes we raised the question whether histamine has any effect on the actual tuning of proper cytokine balance for the proceeding of the gestation. Histamine has multiple functions in the process of pregnancy, different studies have shown the direct and/or indirect presence of histamine action in the placenta as well. As HDC is the unique histamine producing enzyme in eukaryotes, we used HDC (so endogenous histamine)-deficient knockout mice as reliable model for studying histamine-related processes in vivo. We examined the placental histamine content and the expression of histamine receptors and Th1/Th2/Th3 type cytokines in the placenta. We showed for the first time the influence of histamine on the orchestrated regulation of placental cytokine expression. In the absence of local histamine the cytokine balance is shifted toward Th1 types at the maternal-placental interface, threatening pregnancy. We also measured splenic lymphocyte subpopulation ratios in pregnant and non-pregnant mice and found that in pregnancy they are independent of the presence of histamine.

Effect of substance P on uterine mast cell cytokine release during the reproductive cycle

There is increasing evidence that neuropeptides, steroid hormones and inflammatory cytokines influence the immune response during the reproductive cycle. In the present study, we focus on the effects of neuropeptide Substance P (SP) during the pre-implantation stage of embryo development (day 4 of pregnancy), at pro-estrus and di-estrus (two phases with different hormonal states). We found heterogeneous responses to SP and anti-IgE by the rat uterine mast cells (MCs), as detected by ELISA. In fact, MCs purified from uteri on day 4 of pregnancy released histamine, granulocyte macrophage-colony stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha) in response to anti-IgE, but not to SP. When pre-incubated with SP, the release to anti-IgE was significantly enhanced compared to anti-IgE alone. Exposure of SP to antibodies to SP, prior to pre-incubation with MCs, negated the SP effect on IgE-mediated release. At the pro-estrus phase SP showed similar behavior as on day 4 of pregnancy, whereas at the di-estrus phase SP alone was capable of inducing release of histamine and cytokines from purified uterine MCs. Moreover, non-quantitative RT-PCR analysis of the TNF-alpha mRNA level suggested an SP stimulation at the di-estrus phase, but neither on day 4 of pregnancy nor at the pro-estrus phase. Taken together, these data strongly suggest that SP can modulate IgE-mediated uterine MC release of histamine and inflammatory cytokines in different ways, depending on the phase of the reproductive cycle.