Abstract:
Background: 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.
Methods: The abnormal pregnancy model of T. gondii infection was established in C57/B6 pregnant mice and IDO-/- pregnant mice in vivo, and the primary human dMDSCs and dNK cells were cultured in vitro. The expression level of IDO in dMDSCs after T. gondii infection was detected by RT-PCR, flow cytometry and Western Blot. The expression of proteins in the STAT3/p52-RelB signaling pathway in dMDSCs after infection was detected by RTPCR and Western Blot, and then STAT3 phosphorylation inhibitor and p52-RelB nuclear translocation inhibitor were added to block the activation of the pathway, the expression of IDO in dMDSCs was detected by Western Blot to investigate whether the STAT3/p52-RelB signaling pathway affected the expression of IDO in dMDSCs. The expression of SOCS3 in dMDSCs after infection was detected by RT-PCR and Western Blot, and the binding of IDO and SOCS3 after infection was verified by CO-IP, so as to explore the mechanism of action of SOCS3 protein in the change of IDO expression level in dMDSCs induced by T. gondii infection.Transwell co-culture was performed between dMDSCs and dNK cells. Flow cytometry and Western Blot were used to detect the expressions of TGF-β and IL-10 in dNK cells to investigate whether the change of IDO expression level in dMDSCs induced by T. gondii infection affects the dysfunction of dNK cells.To investigate whether the change of IDO expression level in dMDSCs affected the maternal-fetal tolerance function of dNK cells through Kyn/AhR/SP1 signaling pathway after infection, IDO inhibitor, exogenous Kyn, AhR inhibitor and SP1 inhibitor were added into the co-culture system, and the expressions of AhR, SP1, TGF-β and IL-10 in dNK cells were detected by Western Blot. The pregnancy outcome of IDO-/- pregnant mice infected with T. gondii was observed and recorded, and the expression levels of AhR and TGF- β in dNK cells of C57BL/6 pregnant mice and IDO-/- pregnant mice infected with T. gondii were detected by flow cytometry. Exogenous Kyn was used to treat IDO-/- infected pregnant mice, and the mechanism of IDO expression change in dMDSCs after T. gondii infection leading to dNK dysfunction in adverse pregnancy outcomes was explored.
Results: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.
Conclusions: T. gondii infection during pregnancy can synergistically regulate IDO expression in dMDSCs through STAT3/p52-RelB signaling pathway and SOCS3 protein, which in turn affects TGF-β and IL-10 expression in dNK through Kyn/AhR/SP1 signaling pathway, leading to dNK maternal-fetal tolerance dysfunction, which may be an important mechanism for the occurrence of adverse pregnancy outcome due to T. gondii infection.
Biography:
Xuemei Hu , a specialist in immunology, is a professor and doctoral supervisor with a medical doctorate. She completed her postdoctoral research at Harvard University in the United States and is a recipient of the "State Council Special Government Allowance." Recognized as a "Taishan Scholar Distinguished Professor" and an "Outstanding Young and Middle-aged Expert with Significant Contributions" in Shandong Province. Her research domain encompasses reproductive immunology and infection immunology. She has presided over five general projects funded by the National Natural Science Foundation of China . As a corresponding author, she has published over 70 papers.
