Trophoblast?Macrophage Interactions: a Regulatory Network for the Protection of Pregnancy

Chlamydia trachomatis infection modulates trophoblast cytokine/chemokine production

It is well established that intrauterine infections can pose a threat to pregnancy by gaining access to the placenta and fetus, and clinical studies have strongly linked bacterial infections with preterm labor. Although Chlamydia trachomatis (Ct) can infect the placenta and decidua, little is known about its effects on trophoblast cell immune function. We have demonstrated that Ct infects trophoblast cells to form inclusions and completes the life cycle within these cells by generating infectious elementary bodies. Moreover, infection with Ct leads to differential modulation of the trophoblast cell's production of cytokines and chemokines. Using two human first trimester trophoblast cell lines, Sw.71 and H8, the most striking feature we found was that Ct infection results in a strong induction of IL-1beta secretion and a concomitant reduction in MCP-1 (CCL2) production in both cell lines. In addition, we have found that Ct infection of the trophoblast results in the cleavage and degradation of NF-kappaB p65. These findings suggest that the effect of a Chlamydia infection on trophoblast secretion of chemokines and cytokines involves both activation of innate immune receptors expressed by the trophoblast and virulence factors secreted into the trophoblast by the bacteria. Such altered trophoblast innate immune responses may have a profound impact on the microenvironment of the maternal-fetal interface and this could influence pregnancy outcome.

Activation of TLR3 in the trophoblast is associated with preterm delivery

PROBLEM

Toll-like receptors (TLRs) recognize conserved sequences on the surface of pathogens and trigger effector cell functions. Previously, we described the expression of TLR3 by human trophoblast and their ability to respond to (Poly[I:C]). Here we evaluate the effect of Poly[I:C] on mouse pregnancy and characterize the local and systemic response.

METHOD OF STUDY

C57B/6 wild type (wt) and TLR3 knockout (TLR3KO) mice were treated with Poly[I:C] at 16.5 dpc and pregnancy outcome recorded. Morphologic changes, cytokines and chemokines levels in blood and utero-placental tissue were determined. NF-kappaB pathway was evaluated in vivo and in vitro.

RESULTS

Poly[I:C] in C57B/6 wt mice caused preterm delivery within 24 hr (4.5 mg/kg). No effect was observed in TLR3KO mice. In addition, we observed local (placenta) and systemic (serum) response characterized by increased production of proinflammatory cytokines and chemokines. The NF-kappaB pathway was activated by Poly[I:C] in human and mice trophoblast cells.

CONCLUSION

We report that Poly[I:C] induces preterm delivery via TLR3-dependent manner. Furthermore, we demonstrate that the trophoblast is able to recognize Poly[I:C] through TLR3 and respond to viral infection, modulating the immune system at the feto-maternal interface.

Interleukin-6 stimulates cell migration, invasion and integrin expression in HTR-8/SVneo cell line

Interleukin-6 (IL-6) is present in human endometrium throughout menstrual cycle and in pregnancy. Trophoblast also expresses IL-6. IL-6R and its associated signal transducer gp130 were found in trophoblast as well. IL-6 is generally assumed to be relevant for trophoblast invasion. This study was undertaken to determine influence of endogenous and externally added IL-6 on invasion and migration of first trimester of pregnancy trophoblast in vitro. Integrins alpha(5)beta(1) and alpha(1)beta(1) have been shown to play an important role in trophoblast invasion and the effect of IL-6 on the expression of these integrin subunits was studied. We are showing that in both isolated first trimester of pregnancy cytotrophoblast (CTB) and HTR-8/SVneo cell line IL-6 and IL-6R are present. The effect on migration was studied using cell wounding and migration test on HTR-8/SVneo cells. Effect of IL-6 and function blocking anti-IL-6 antibody in Matrigel invasion tests was studied on both cell types. The effect of IL-6 on integrin subunit expression was determined by cell-based ELISA and Western blot on HTR-8/SVneo cells. The results obtained show that exogenous IL-6 has stimulatory effect on cell migration in HTR-8/SVneo and invasion by both cell types. Function blocking anti-IL-6 inhibited unstimulated invasion by isolated first trimester cytotrophoblast and both cell migration and invasion in unstimulated HTR-8/SVneo. Integrin alpha(5) expression was stimulated by IL-6 to 134% (p<0.05), alpha(1) to 135% (p<0.005), and beta(1) to 134% (p<0.001) of control in cell-based ELISA, but also in Western blot. The data obtained show for the first time sensitivity of extravillous trophoblast cell line HTR-8/SVneo to IL-6, in addition to isolated first trimester cytotrophoblast. We conclude that both exogenous and endogenous IL-6 stimulate trophoblast cell migration and invasion, which may be partly attributable to stimulation of expression of the studied integrin subunits.

Promotion of angiogenesis by human endometrial lymphocytes

The human endometrium is a unique tissue that undergoes dramatic monthly remodeling during the menstrual cycle in preparation for an implanting conceptus. This remodeling involves sequential proliferation and differentiation of endometrial stromal and epithelial cells, coupled with extensive angiogenesis and infiltration of a specific specialized immune cell subset. Increasing evidence points to an essential role for these maternal leukocytes in stimulating the endometrial angiogenesis, and we propose that they also play a key role in the decidual vascular transformation. Aberrant endometrial angiogenesis, decidualisation and vascular transformation is thought to underlie many pathologies of pregnancy, from infertility to the development of preeclampsia and Intra Uterine Growth Restriction. In this chapter we review the cellular processes associated with each stage of endometrial and decidual transformation, detailing the role of the immune cell populations and the angiogenic and chemotactic factors secreted by them.

Deviations in populations of peripheral blood mononuclear cells and endometrial macrophages in the cow during pregnancy

The presence of conceptus alloantigens necessitates changes in maternal immune function. Here, we used the cow to evaluate whether species with epitheliochorial placentation have changes in specific leukocyte populations during pregnancy similar to those reported in species with hemotropic placentae. At days 33–34 of pregnancy, there was no effect of pregnancy status on the number of cells positive for CD8, CD4, γδT cell receptor, or the monocyte marker CD68 in the peripheral blood mononuclear cell (PBMC) population. There was, however, an increase in the proportion of CD4+cells that were positive for CD25. There was no effect of status on the proportion of PBMCs that were CD8+when comparing preparturient cows to nonpregnant cows. However, preparturient cows had an increased percentage of PBMCs that were γδT cells and CD4+CD25+and a tendency for a lower percentage that were CD68+cells. Using immunolocalization with anti-CD68, it was found that pregnant cows had increased numbers of CD68+cells in the endometrial stroma as early as days 54–100 of gestation; this increase persisted through the last time examined (day 240 of gestation). Cells positive for CD68 were also positive for another macrophage/monocyte marker, CD14. In conclusion, pregnancy in the cow is associated with changes in peripheral and endometrial leukocyte numbers, which are similar to patterns observed in other species.

Inflammation and pregnancy: the role of toll-like receptors in trophoblast-immune interaction

During normal pregnancy, the decidua is populated by a variety of leucocytes; however, cells of the innate immune system seem to dominate this tissue. Their presence suggests that the innate immune system is not indifferent to the fetus and has been associated with a response of the maternal immune system to the "semi-allograft fetus." New evidences, however, indicates that these immune cells are critical for decidual and trophoblast development, rather than induction of tolerance. We hypothesized that, during implantation, an inflammatory environment is necessary for the attachment and invasion of the blastocyst. Therefore, we propose the existence of an "inflammatory-mediated embryo implantation" condition that is dependent on the proper "education" of the innate immune system by the trophoblast. Here we postulate that trophoblast cells successfully orchestrate their inflammatory environment and regulate immune cell differentiation and activation.

TLR6 modulates first trimester trophoblast responses to peptidoglycan

Intrauterine bacterial infections are a well-established cause of pregnancy complications. One key observation in a number of abnormal pregnancies is that placental apoptosis is significantly elevated. First trimester trophoblast cells are known to express TLR1 and TLR2 and to undergo apoptosis following exposure to Gram-positive bacterial peptidoglycan (PDG). Thus, the objectives of this study were to determine whether PDG-induced pregnancy complications are associated with placental apoptosis and to characterize the cellular mechanisms involved. We have demonstrated, using an animal model, that delivery of PDG to pregnant mice early in gestation resulted in highly elevated placental apoptosis, evidenced by trophoblast M-30 and active caspase 3 immunostaining. Using an in vitro model of human first trimester trophoblasts, apoptosis induced by PDG was found to be mediated by both TLR1 and TLR2 and that this could be blocked by the presence of TLR6. Furthermore, in the presence of TLR6, exposure to PDG resulted in trophoblast NF-kappaB activation and triggered these cells to secrete IL-8 and IL-6. The findings of this study suggest that a Gram-positive bacterial infection, through TLR2 and TLR1, may directly promote the elevated trophoblast cell death and that this may be the underlying mechanism of pregnancy complications, such as preterm delivery. Furthermore, the expression of TLR6 may be a key factor in determining whether the response to PDG would be apoptosis or inflammation.

Expression and function of toll-like receptors at the maternal-fetal interface

Toll-like receptors (TLRs) form the major family of pattern recognition receptors that are involved in innate immunity. Innate immune responses against microorganisms at the maternal-fetal interface may have a significant impact on the success of pregnancy because intrauterine infections have been shown to be strongly associated with certain complications of pregnancy. At the maternal-fetal interface, TLRs are expressed not only in the immune cells but also in nonimmune cells such as trophoblasts and decidual cells. Moreover, their expression patterns vary according to the stage of pregnancy. Here we will describe potential functions of TLRs in these cells, their recognition and response to microorganisms, and their involvement in the innate immunity. The impact of TLR-mediated innate immune response will be discussed via animal model studies, as well as clinical observations.

Chemokine decoy receptors: new players in reproductive immunology

Chemokines are multifunctional molecules with roles in leukocyte trafficking and developmental processes. Both fetal and maternal components of the placenta produce chemokines, which control leukocyte trafficking observed in the placenta. Thus, chemokines play roles in the balance between protection of the developing embryo/fetus and tolerance of its hemiallogeneic tissues. Recently, a group of chemokine receptors, which include D6, DARC, and CCX-CKR, have been described as "silent" receptors by virtue of their inability to activate signal transduction events leading to cell chemoattraction. Here we review in vitro and in vivo evidence indicating that chemokine "silent" receptors regulate innate and adaptive immunity behaving as decoy receptors that support internalization and degradation of chemotactic factors, and discuss available information on their potential role in reproductive immunology.

Antigen-presenting cells and materno-fetal tolerance: an emerging role for dendritic cells

During pregnancy, a delicate balance of innate and adaptive immune responses at the maternal-fetal interface promotes survival of the semi-allogeneic embryo and, at the same time, allows effective immunity to protect the mother from environmental pathogens. As in other tissues, antigen handling and processing in the decidualized endometrium constitutes a primary event in the onset of immune responses and is therefore likely to determine their stimulatory or tolerogenic nature. Maternal antigen-presenting cells [macrophages and dendritic cells (DCs)] are scattered throughout the decidualized endometrium during all stages of pregnancy and appear to be important players in this feto-maternal immune adjustment. This review focuses on the characterization of decidual macrophages and DCs, as well as their involvement in cell-cell interactions within the decidual leukocyte network, which are likely to influence uterine and placental homeostasis as well as the local maternal immune responses to the fetus during pregnancy.

A novel three-dimensional in vitro system to study trophoblast-endothelium cell interactions

INTRODUCTION

Pregnancy complications have been linked to improper trophoblast migration and failure of spiral artery transformation. Endothelial cells play an essential role in directing trophoblast migration and transformation, although by an unknown mechanism. We describe a novel in vitro model to evaluate endothelial-trophoblast interaction and signaling in a three-dimensional system.

METHOD OF STUDY

Immortalized human endometrial endothelial cell line and first trimester trophoblast cells were co-cultured. Endothelial transformation into vessel-like structures occurred in Matrigel(TM) OpenLab Image Analysis software was used to monitor labeled trophoblast migration and endothelium transformation. Cytokine/chemokine production was determined using Multiplex.

RESULTS

Trophoblast migrates toward endothelial cells in Matrigel, aligns on top of the endothelium within 4-8 hr and achieves complete replacement of the endothelium by 72-96 hr. Lipopolysaccharide treatment damages the endothelium and disrupts endothelium-trophoblast interaction.

CONCLUSION

We report a novel three-dimensional in vitro and in vivo system of trophoblast-endothelium cell interaction. Significant changes in endothelial cells' phenotype are observed upon differentiation in Matrigel. These changes may be necessary for endothelium to direct trophoblast migration and transformation.

Immunology of pregnancy: cellular mechanisms allowing fetal survival within the maternal uterus

Pregnancy success remains a fascinating phenomenon to immunologists as it defies the immunological rules of rejection. Although it was previously thought that the maternal immune system does not see the fetus, it is now well documented that fetal cells reach the maternal body and encounter host immune cells. Natural tolerance mechanisms following this interaction remain to be fully elucidated. This article reviews the current literature on mechanisms of adaptive immunity, with emphasis on regulatory T cells and heme oxygenase 1 (HO-1). We propose a scenario in which regulatory T cells create a tolerant microenvironment at the fetal-maternal interface characterised by the presence of tolerance-associated molecules such as HO-1, which has been shown to be of vital importance for fetal survival.