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Myeloid-derived suppressor cells (MDSCs) play a key role in maintaining maternal-fetal tolerance for a successful pregnancy, but the role of MDSCs in abnormal pregnancy caused by Toxoplasma gondii infection is unknown. Herein, we revealed a distinct mechanism by which T-cell immunoglobulin domain and mucin domain containing protein-3 (Tim-3), an immune checkpoint receptor that balances maternal-fetal tolerance during pregnancy, contributes to the immunosuppressive function of MDSCs during T. gondii infection. The expression of Tim-3 in decidual MDSCs was significantly downregulated following T. gondii infection. The proportion of monocytic MDSCs population, the inhibitory effect of MDSCs on T-cell proliferation, the levels of STAT3 phosphorylation, and the expression of functional molecules (Arg-1 and IL-10) in MDSCs were all decreased in T. gondii-infected pregnant Tim-3 gene knockout (Tim-3KO) mice compared with infected pregnant WT mice. After treatment with Tim-3-neutralizing Ab in vitro, the expression levels of Arg-1, IL-10, C/EBPβ, and p-STAT3 were decreased, the interaction between Fyn and Tim-3 or between Fyn and STAT3 was weakened, and the binding ability of C/EBPβ to the promoters of ARG1 and IL10 was decreased in human decidual MDSCs with T. gondii infection, while opposite results were observed following treatment with galectin-9 (a ligand for Tim-3). Inhibitors of Fyn and STAT3 also downregulated the expression of Arg-1 and IL-10 in decidual MDSCs and exacerbated adverse pregnancy outcomes caused by T. gondii infection in mice. Therefore, our studies discovered that the decrease of Tim-3 after T. gondii infection could downregulate the functional molecules of Arg-1 and IL-10 expression in decidual MDSCs through the Fyn-STAT3-C/EBPβ signaling pathway and weaken their immunosuppressive function, which eventually contribute to the development of adverse pregnancy outcomes. Author summary: Pregnant women in their first trimester with a primary infection of T. gondii are particularly susceptible resulting in a number of serious adverse pregnancy outcomes. Previous studies have shown that T. gondii infection results in the dysfunction of immune cell function at the maternal-fetal interface, which destroys the function of maternal-fetal immune tolerance for a successful pregnancy. MDSCs have an immunosuppressive capacity and play an important role in the maintenance of normal pregnancy. However, the role of MDSCs in the adverse pregnancy outcomes caused by T. gondii infection remains unknown. Here, we analyzed the effect of an immunosuppressive molecule Tim-3 on the function of decidual MDSCs following T. gondii infection. Our results showed that T. gondii infection downregulated the proportion of monocytic MDSCs population, the inhibitory ability of MDSCs on T cell proliferation, the level of STAT3 phosphorylation, and the expression of functional molecules (Arg-1 and IL-10) in MDSCs from the pregnant Tim-3KO mice compared with the pregnant WT mice. Further study showed that the decrease of Tim-3 expression caused by T. gondii infection could downregulate Arg-1 and IL-10 expression in decidual MDSCs via the Fyn-STAT3-C/EBPβ signaling pathway and weaken their immunosuppressive function. This work suggested that MDSCs dysfunction resulting from the downregulation of Tim-3 after T. gondii infection may be an important mechanism of adverse pregnancy outcomes, which may provide theoretical information for prophylactic and/or therapeutic treatments against the infection-related abnormal pregnancy. [ABSTRACT FROM AUTHOR]

Myeloid-derived suppressor cells (MDSCs) play a crucial role in maintaining maternal-fetal tolerance by expressing some immune-suppressive molecules, such as indoleamine 2,3-dioxygenase (IDO). Toxoplasma gondii (T. gondii) infection can break the immune microenvironment of maternal-fetal interface, resulting in adverse pregnancy outcomes. However, whether T. gondii affects IDO expression in dMDSCs and the molecular mechanism of its effect are still unclear. Here we show, the mRNA level of IDO is increased but the protein level decreased in infected dMDSCs. Mechanistically, the upregulation of transcriptional levels of IDO in dMDSCs is regulated through STAT3/p52-RelB pathway and the decrease of IDO expression is due to its degradation caused by increased SOCS3 after T. gondii infection. In vivo, the adverse pregnancy outcomes of IDO−/− infected mice are more severe than those of wide-type infected mice and obviously improved after exogenous kynurenine treatment. Also, the reduction of IDO in dMDSCs induced by T. gondii infection results in the downregulation of TGF-β and IL-10 expression in dNK cells regulated through Kyn/AhR/SP1 signal pathway, eventually leading to the dysfunction of dNK cells and contributing the occurrence of adverse pregnancy outcomes. This study reveals a novel molecular mechanism in adverse pregnancy outcome induced by T. gondii infection. IDO downregulation in dMDSCs induced by Toxoplasma gondii infection regulates expression of TGF-β and IL-10 through the Kyn/AhR/SP1 signal pathway, eventually contributing to the dysfunction of dNK cells. [ABSTRACT FROM AUTHOR]

Background: Toxoplasma gondii infection can cause adverse pregnancy outcomes, such as recurrent abortion, fetal growth restriction and infants with malformations, among others. Decidual myeloid-derived suppressor cells (dMDSCs) are a novel immunosuppressive cell type at the fetal-maternal interface which play an important role in sustaining normal pregnancy that is related to their high expression of the inhibitory molecule leukocyte immunoglobulin-like receptor B4 (LILRB4). It has been reported that the expression of LILRB4 is downregulated on decidual macrophages after T. gondii infection, but it remains unknown whether T. gondii infection can induce dMDSC dysfunction resulting from the change in LILRB4 expression. Methods: LILRB4-deficient (LILRB4−/−) pregnant mice infected with T. gondii with associated adverse pregnancy outcomes, and anti-LILRB4 neutralized antibodies-treated infected human dMDSCs were used in vivo and in vitro experiments, respectively. The aim was to investigate the effect of LILRB4 expression on dMDSC dysfunction induced by T. gondii infection. Results: Toxoplasma gondii infection was observed to reduce STAT3 phosphorylation, resulting in decreased LILRB4 expression on dMDSCs. The levels of the main functional molecules (arginase-1 [Arg-1], interleukin-10 [IL-10]) and main signaling molecules (phosphorylated Src-homology 2 domain-containing protein tyrosine phosphatase [p-SHP2], phosphorylated signal transducer and activator of transcription 6 [p-STAT6]) in dMDSCs were all significantly reduced in human and mouse dMDSCs due to the decrease of LILRB4 expression induced by T. gondii infection. SHP-2 was found to directly bind to STAT6 and STAT6 to bind to the promoter of the Arg-1 and IL-10 genes during T. gondii infection. Conclusions: The downregulation of LILRB4 expression on dMDSCs induced by T. gondii infection could regulate the expression of Arg-1 and IL-10 via the SHP-2/STAT6 pathway, resulting in the dysfunction of dMDSCs, which might contribute to adverse outcomes during pregnancy by T. gondii infection. [ABSTRACT FROM AUTHOR]

Background: Toxoplasma gondii infection during pregnancy can lead to fetal defect(s) or congenital complications. The inhibitory molecule B7-H4 expressed on decidual macrophages (dMφ) plays an important role in maternal–fetal tolerance. However, the effect of B7-H4 on the function of dMφ during T. gondii infection remains unclear. Methods: Changes in B7-H4 expression on dMφ after T. gondii infection were explored both in vivo and in vitro. B7-H4-/- pregnant mice (pregnant mice with B7-H4 gene knockout) and purified primary human dMφ treated with B7-H4 neutralizing antibody were used to explore the role of B7-H4 signaling on regulating the membrane molecules, synthesis of arginine metabolic enzymes and cytokine production by dMφ with T. gondii infection. Also, adoptive transfer of dMφ from wild-type (WT) pregnant mice or B7-H4-/- pregnant mice to infected B7-H4-/- pregnant mice was used to examine the effect of B7-H4 on adverse pregnancy outcomes induced by T. gondii infection. Results: The results illustrated that B7-H4-/- pregnant mice infected by T. gondii had poorer pregnancy outcomes than their wild-type counterparts. The expression of B7-H4 on dMφ significantly decreased after T. gondii infection, which resulted in the polarization of dMφ from the M2 toward the M1 phenotype by changing the expression of membrane molecules (CD80, CD86, CD163, CD206), synthesis of arginine metabolic enzymes (Arg-1, iNOS) and production of cytokines (IL-10, TNF-α) production. Also, we found that the B7-H4 downregulation after T. gondii infection increased iNOS and TNF-α expression mediated through the JAK2/STAT1 signaling pathway. In addition, adoptive transfer of dMφ from a WT pregnant mouse donor rather than from a B7-H4-/- pregnant mouse donor was able to improve adverse pregnancy outcomes induced by T. gondii infection. Conclusions: The results demonstrated that the downregulation of B7-H4 induced by T. gondii infection led to the dysfunction of decidual macrophages and contributed to abnormal pregnancy outcomes. Moreover, adoptive transfer of B7-H4+ dMφ could improve adverse pregnancy outcomes induced by T. gondii infection. [ABSTRACT FROM AUTHOR]

Background: Women in early pregnancy infected by Toxoplasma gondii may have severe adverse pregnancy outcomes, such as spontaneous abortion and fetal malformation. The inhibitory molecule T cell immunoglobulin and mucin domain 3 (Tim-3) is highly expressed on decidual dendritic cells (dDCs) and plays an important role in maintaining immune tolerance. However, whether T. gondii infection can cause dDC dysfunction by influencing the expression of Tim-3 and further participate in adverse pregnancy outcomes is still unclear. Methods: An abnormal pregnancy model in Tim-3-deficient mice and primary human dDCs treated with Tim-3 neutralizing antibodies were used to examine the effect of Tim-3 expression on dDC dysfunction after T. gondii infection. Results: Following T. gondii infection, the expression of Tim-3 on dDCs was downregulated, those of the pro-inflammatory functional molecules CD80, CD86, MHC-II, tumor necrosis factor-α (TNF-α), and interleukin-12 (IL-12) were increased, while those of the tolerant molecules indoleamine 2,3-dioxygenase (IDO) and interleukin-10 (IL-10) were significantly reduced. Tim-3 downregulation by T. gondii infection was closely associated with an increase in proinflammatory molecules and a decrease in tolerant molecules, which further resulted in dDC dysfunction. Moreover, the changes in Tim-3 induced by T. gondii infection further reduced the secretion of the cytokine IL-10 via the SRC-signal transducer and activator of transcription 3 (STAT3) pathway, which ultimately contributed to abnormal pregnancy outcomes. Conclusions: Toxoplasma gondii infection can significantly downregulate the expression of Tim-3 and cause the aberrant expression of functional molecules in dDCs. This leads to dDC dysfunction, which can ultimately contribute to abnormal pregnancy outcomes. Further, the expression of the anti-inflammatory molecule IL-10 was significantly decreased by Tim-3 downregulation, which was mediated by the SRC-STAT3 signaling pathway in dDCs after T. gondii infection. [ABSTRACT FROM AUTHOR]

A Toxoplasma gondii infection during pregnancy can result in spontaneous abortion, preterm labor, or congenital fetal defects. The decidual immune system plays a critical role in regulating the immune micro-environment and in the induction of immune tolerance. To better understand the factors that mediate the decidual immune response associated with the T. gondii infection, a large-scale study employing TMT proteomics was conducted to characterize the differential decidual immune proteomes from infected and uninfected human decidual immune cells samples. The decidual immune cells from 105 human voluntary abortion tissues were purified, and of the 5510 unique proteins identified, 181 proteins were found to be differentially abundant (>1.2-fold cutoff, p <  0.05) in the T. gondii -infected decidual immune cells. 11 proteins of 181 differentially expressed proteins associated with trophoblast invasion, placental development, intrauterine fetal growth, and immune tolerance were verified using a quantitative real-time polymerase chain reaction and western blotting. This systematic analysis for the proteomics of decidual immune cells identified a broad range of immune factors in human decidual immune cells, shedding a new insight into the decidual immune molecular mechanism for abnormal pregnancy outcomes associated with T. gondii infection. [ABSTRACT FROM AUTHOR]