Toll-like Receptors and Pregnancy

Trophoblast-secreted soluble-PD-L1 modulates macrophage polarization and function

Decidual macrophages are in close contact with trophoblast cells during placenta development, and an appropriate crosstalk between these cellular compartments is crucial for the establishment and maintenance of a healthy pregnancy. During different phases of gestation, macrophages undergo dynamic changes to adjust to the different stages of fetal development. Trophoblast-secreted factors are considered the main modulators responsible for macrophage differentiation and function. However, the phenotype of these macrophages induced by trophoblast-secreted factors and the factors responsible for their polarization has not been elucidated. In this study, we characterized the phenotype and function of human trophoblast-induced macrophages. Using in vitro models, we found that human trophoblast-educated macrophages were CD14⁺ CD206⁺ CD86^- and presented an unusual transcriptional profile in response to TLR4/LPS activation characterized by the expression of type I IFN-β expression. IFN-β further enhances the constitutive production of soluble programmed cell death ligand 1 (PD-L1) from trophoblast cells. PD-1 blockage inhibited trophoblast-induced macrophage differentiation. Soluble PD-L1 (sPD-L1) was detected in the blood of pregnant women and increased throughout the gestation. Collectively, our data suggest the existence of a regulatory circuit at the maternal fetal interface wherein IFN-β promotes sPD-L1 expression/secretion by trophoblast cells, which can then initiate a PD-L1/PD-1-mediated macrophage polarization toward an M2 phenotype, consequently decreasing inflammation. Macrophages then maintain the expression of sPD-L1 by the trophoblasts through IFN-β production induced through TLR4 ligation.

Relevance of placental type I interferon beta regulation for pregnancy success

Pregnancy is a unique immunologic and microbial condition that requires an adequate level of awareness to provide a fast and protective response against pathogens as well as to maintain a state of tolerance to paternal antigens. Dysregulation of inflammatory pathways in the placenta triggered by pathogens is one of the main factors responsible for pregnancy complications. Type I IFNs are key molecules modulating immune responses at the level of the placenta and are crucial for protection of the pregnancy via their antiviral and immune modulatory properties. In this study, we elucidate the mechanisms controlling the basal expression of IFNβ and its negative feedback. Using in vitro and in vivo animal models, we found that TLR signaling maintains basal IFNβ levels through the TLR4-MyD88-independent TBK/IRF3 signaling pathway. We describe the role of the TAM receptor Axl in the regulation of IFNβ function in human and mouse trophoblast cells. The absence of TAM receptors in vivo is associated with fetal demise due to dysregulation of IFNβ expression and its pro-apoptotic downstream effectors. Collectively, our data describe a feedback signaling pathway controlling the expression and function of IFNβ in the trophoblast that is essential for an effective response during viral and microbial infections.

Early pregnancy-related changes in toll-like receptors expression in ovine trophoblasts and peripheral blood leukocytes

In the present study, we aimed to 1) demonstrate the presence of all 10 toll-like receptors (TLRs) in ovine trophoblasts, and 2) investigate the expression profiles of TLR1-10 mRNAs in peripheral blood leukocytes (PBLs) in ewes during early pregnancy. For those purposes, ovine trophoblasts (n = 6) were collected from pregnant ewes on day 13. PBLs were collected from non-pregnant (n = 6) and pregnant ewes (n = 17) on days of mating (d) 0 and 18. TLR mRNAs in ovine trophoblasts were visualized by free-floating in situ hybridization (ISH). To assess the expression profiles of TLR1-10 in PBLs, total RNA was isolated and transcribed to cDNA. TLR1-10 mRNA levels were determined by real-time PCR in triplicate. The Relative Expression Software Tool (REST 2009) was used for statistical analysis. We detected mRNAs for TLR2, TLR4, TLR5, TLR6, TLR7, TLR8, and TLR10 but not for TLR1, TLR3, and TLR9 in trophoblasts. TLR2, TLR5, TLR6, TLR7, TLR8, and TLR10 mRNAs were expressed by all trophoblasts, whereas TLR4 mRNA and protein in trophoblasts were more limited. In PBLs, TLR expression did not differ between day 0 and day 18 in non-pregnant ewes; however, ewes in early pregnancy exhibited significantly upregulated expression of TLR2 (2.3-fold), TLR4 (3.1-fold), TLR6 (1.7-fold), and TLR8 (2.2-fold) on day 18 compared with day 0. In contrast, TLR10 was downregulated (2-fold) on day 18 by pregnancy. Similar results were also obtained for TLR2, TLR4, TLR6, TLR8 and TLR10 from the comparison between day 18 non -pregnant and day 18 pregnant groups. According to these results, the presence of TLRs in early ovine trophoblasts suggests that these cells play an immunological role at the maternal-fetal interface. The results also suggest that tight regulation of some components of TLRs in PBLs due to embryo- and/or pregnancy-related factors is necessary for successful establishment of early pregnancy in ewes.

Toll-like receptors at the maternal-fetal interface in normal pregnancy and pregnancy complications

Toll-like receptors (TLRs) form the major family of pattern recognition receptors (PRRs) 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, as 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 non-immune cells such as trophoblasts and decidual cells; moreover, their expression patterns vary according to the stage of pregnancy. Here, we will update 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.

Expression and localization of TLR4 and its negative regulator Tollip in the placenta of early-onset and late-onset preeclampsia

OBJECTIVE

Toll-like receptor 4 (TLR4) is a key component of the innate arm of the immune system that mediates inflammatory responses following exposure to bacterial lipopolysaccharides. In doing so, TLR4 may contribute to the pathogenesis of preeclampsia (PE). We sought to assess the spatio-temporal expression of TLR4 and its negative regulator Toll-interacting protein (Tollip) in placental tissues from normal and preeclamptic pregnancies.

METHODS

Using immunohistochemistry and immunoblotting, we investigated the localization of TLR4 and its negative regulator Tollip in first- and third-trimester human placenta.

RESULTS

TLR4 was found to be expressed in the cytoplasm of trophoblasts in both first- (n = 6) and third-trimester (n = 24) placental villous samples. Tollip was mainly located in the cytoplasm of cytotrophoblasts in the first-trimester placental tissues; in contrast, our analyses of third-trimester placental tissues demonstrated that Tollip was mainly located in the decidual cells. Using western blot analysis, TLR4 expression was shown to be significantly higher in early-onset PE tissues than control group placentas (n = 8 for each group, p < 0.01). However, we were unable to detect a significant difference between late-onset PE and normal controls (n = 8 for each group, p = 0.119).

CONCLUSION

These data demonstrate the novel observation that TLR4 may play a much more important role in early-onset PE. Interestingly, the spatial expression of Tollip at different stages of gestation may play an important role in the pathophysiology of PE.

Prevention of inflammatory activation of human gestational membranes in an ex vivo model using a pharmacological NF-kappaB inhibitor

Intrauterine inflammation plays a major role in the etiology of preterm labor and birth. We established an ex vivo model employing perfused full-thickness term gestational membranes to study membrane transport, function, and inflammatory responses. Exposure of the maternal (decidual) face of the membranes to LPS (5 microg/ml) resulted in increased accumulation of proinflammatory cytokines in the maternal compartment within 4 h, followed by a response in the fetal (amniotic) compartment. Using cytokine arrays, exposure to LPS was found to result in increased secretion of a large number of cytokines and chemokines in both compartments, most notably IL-5, IL-6, IL-7, MDC (macrophage-derived chemokine), MIG (monokine induced by IFN-gamma), TARC (thymus and activation-regulated chemokine), TGF-beta, and TNF-alpha. PGE(2) accumulation also increased in response to LPS, particularly in the fetal compartment. Cotreatment with sulfasalazine, which inhibited nuclear translocation of NF-kappaB p65, had a rapid and marked inhibitory effect on the rate of cytokine accumulation in the maternal compartment, with lesser but significant effects observed in the fetal compartment. While membrane integrity was not discernibly impaired with LPS or sulfasalazine exposure, rates of chorionic apoptosis after 20 h were doubled in sulfasalazine-treated tissues. We conclude that the system described provides a means of accurately modeling human gestational membrane functions and inflammatory activation ex vivo. Decidual LPS exposure was shown to elicit a robust inflammatory response in both the maternal and fetal compartments. Sulfasalazine was an effective antiinflammatory agent in this model, but also exerted proapoptotic effects that raise concerns regarding its placental effects when administered in pregnancy.

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.