Accumulation of γδT cells in the decidua is promoted by RANKL which upregulates ICAM-1 via NF-κB.

In brief: The mechanism underlying the accumulation of γδT cells in the decidua, which helps maintain maternal-fetal immunotolerance in early pregnancy, is unknown. This study reveals that DSC-derived RANKL upregulates ICAM-1 expression via the NF-κB pathway to enable γδT cell accumulation in the early decidua. Abstract: Decidual γδT (dγδT) cells help maintain maternal-fetal immunotolerance in early pregnancy. However, the mechanism underlying the accumulation of γδT cells in the decidua is unknown. Previous work showed that RANKL upregulated intercellular adhesion molecule 1 (ICAM-1) in decidual stromal cells (DSCs), and Rankl knockout mice had limited dγδT cell populations. In this study, we measured the expression levels of RANKL/RANK and ICAM-1 in DSCs, in addition to the integrins of ICAM-1 on dγδT cells, and the number of dγδT cells from patients with recurrent spontaneous abortion (RSA) and normal pregnant women in the first trimester. RSA patients showed significantly decreased RANKL/RANK and ICAM-1/CD11a signaling in decidua, and a decreased percentage of dγδT cells, which was positively correlated with DSC-derived RANKL and ICAM-1. Next, an in vitro adhesion experiment showed that the enhanced attraction of human DSCs to dγδT cells after RANKL overexpression was almost completely aborted by anti-ICAM-1. Furthermore, Rankl knockout mice showed a significant reduction in NF-κB activity compared with wild-type controls. Finally, we applied a selective NF-κB inhibitor named PDTC to validate the role of NF-κB in RANKL-mediated ICAM-1 upregulation. Taken together, our data show that DSC-derived RANKL upregulates ICAM-1 expression via the NF-κB pathway to enable γδT cell accumulation in the early decidua. A reduction in RANKL/ICAM-1 signaling in DSCs may result in insufficient accumulation of γδT cells in decidua and, in turn, RSA.

GAS6-mediated dialogue between decidual stromal cells and macrophages is essential for early pregnancy maintenance by inducing M2-like polarization and cell proliferation of decidual macrophages.

Maternal immunotolerance towards the semi-allogeneic foetus is critical for normal pregnancy (NP). As a secretory protein, growth arrest-specific factor 6 (GAS6) promotes cancer progression by inducing the conversion of tumour-associated macrophages to an immunosuppressive M2-like phenotype. However, little is known about whether GAS6 regulates decidual macrophages (dMφs) in the early maternal-foetal interface. In this study, first-trimester decidual tissues were obtained from normal pregnant women undergoing elective terminations and patients with miscarriages. The expression of GAS6 and its receptors (AXL, TYRO3 and MERTK) in decidua and GAS6 secretion by decidual stromal cells (DSCs) was measured. Then, we investigated the effect of recombinant human GAS6 (rhGAS6) on dMφs isolated from NP and THP-1 cells, and revealed the underlying mechanism. Both the expression of GAS6 in DSCs and MERTK in dMφs, in addition to GAS6 secretion by DSCs, was found to be significantly decreased in miscarriage patients compared to that in NPs. Additionally, we observed that rhGAS6 polarized dMφs and THP-1 cells towards an M2-like phenotype, as evidenced by the up-regulated CD163 expression. Moreover, rhGAS6 enhanced the clearance of toxic cell-free haemoglobin by dMφs by up-regulating CD163 expression, and rhGAS6 also boosted cell proliferation of dMφs and THP-1 cells. Finally, we demonstrated that rhGAS6 stimulated CD163 expression and cell proliferation by activating the PI3K/Akt signalling pathway. Collectively, these findings suggest that GAS6-mediated dialogue between DSCs and dMφs is crucial for the establishment and maintenance of maternal-foetal immunotolerance, and decreased GAS6 secretion by DSCs may lead to the occurrence of miscarriage in the first trimester.