In this study, we aimed to investigate the expression of OX40, OX40L, PD-1 and PD-L1 in patients with unexplained recurrent spontaneous abortion (URSA) compared to normal pregnancies (NP). A total of 50 patients who were diagnosed with URSA and 41 NP were recruited to this study. Real-time polymerase chain reaction (RT-PCR) was used to determine the expression of OX40, OX40L, PD-1 and PD-L1 in decidual tissues; Immunohistochemistry (IHC) was conducted to characterize the distribution of the involved genes in decidual tissues; Double immunofluorescence staining was used to prove the localization of the involved genes in decidual tissues. The concentrations of OX40L and PD-L1 in plasma were measured with enzyme-linked immunosorbent assay (ELISA). The expression of OX40L in the decidua of URSA patients was significantly increased compared to that in the NP group, while the expression of PD-L1 in the URSA group was decreased compared to that in the NP group. Both proteins are localized in the decidual stroma as analyzed by double immunofluorescence staining. The staining results were confirmed at the mRNA level of decidual tissues, while the mRNA level of peripheral blood showed no significant difference. In conclusion, the results suggest that decidual stromal cells may promote the interaction with OX40 on T cells by upregulating the expression of OX40L and reduce the interaction with PD-1 on T cells by downregulating the expression of PD-L1 in URSA patients, which may interfere with the immune tolerance of the maternal-fetal interface, leading to poor pregnancy outcomes.

在本研究中，我们旨在探讨与正常妊娠 (NP) 相比，不明原因复发性流产 (URSA)患者中OX40、OX40L、PD-1 和 PD-L1 的表达情况。本研究共招募了 50 名被诊断为 URSA 的患者和 41 名 NP 患者。采用实时聚合酶链式反应（RT-PCR）测定蜕膜组织中OX40、OX40L、PD-1、PD-L1的表达量；进行免疫组织化学（IHC）来表征相关基因在蜕膜组织中的分布；使用双重免疫荧光染色来证明相关基因在蜕膜组织中的定位。采用酶联免疫吸附试验（ELISA）测定血浆中OX40L和PD-L1的浓度。URSA患者蜕膜中OX40L的表达量较NP组显着升高,而URSA组PD-L1的表达量较NP组下降。通过双重免疫荧光染色分析，两种蛋白质都位于蜕膜基质中。染色结果在蜕膜组织的mRNA水平得到证实，而外周血的mRNA水平无显着差异。总之，结果表明，在URSA患者中，蜕膜基质细胞可能通过上调OX40L的表达促进与T细胞上OX40的相互作用，并通过下调PD-L1的表达来减少与T细胞上PD-1的相互作用，这可能干扰母胎界面的免疫耐受，导致不良妊娠结局。