Programmed death ligand (PD-L) 2 and PD-L1 are the second and first ligands, respectively, for programmed cell death-1 protein (PD-1), which is one of the key factors responsible for inhibitory T cell signaling, mediating mechanisms of tolerance and providing immune homeostasis. Studies have shown that PD-1 and its ligand PD-L1 are abnormally expressed in autoimmune diseases, such as rheumatoid arthritis and autoimmune hepatitis, but its other ligand, PD-L2, has rarely been studied. This study analyzed the changes in membrane-bound PD-L2 expression in peripheral blood mononuclear cells and soluble PD-L2 (sPD-L2) levels in the serum of patients with systemic lupus erythematosus (SLE) to explore the relationship between PD-L2 expression with disease activity and related test parameters. Our results showed that membrane-bound PD-L2 expression on monocytes was significantly higher and the sPD-L2 levels were significantly lower in SLE patients than in healthy subjects. Patients with active SLE accompanied by lupus nephritis, joint pain, and clinical manifestations of oral ulcers had relatively low secretion of sPD-L2. In addition, this secretion level was significantly and positively correlated with complement components 3 and 4 (C3/C4). These results suggest that PD-L2 may be a promising biomarker associated with the pathogenesis of SLE.

程序性死亡配体 (PD-L) 2 和 PD-L1 分别是程序性细胞死亡 1 蛋白 (PD-1) 的第二和第一配体，PD-1 是负责抑制性 T 细胞信号传导的关键因素之一，介导耐受机制和提供免疫稳态。研究表明，PD-1及其配体PD-L1在类风湿性关节炎、自身免疫性肝炎等自身免疫性疾病中异常表达，但其另一配体PD-L2却鲜有研究。本研究通过分析系统性红斑狼疮（SLE）患者外周血单个核细胞膜结合PD-L2表达及血清可溶性PD-L2（sPD-L2）水平的变化，探讨PD-L2表达的关系与疾病活动性和相关的测试参数。我们的结果表明，与健康受试者相比，SLE 患者单核细胞上的膜结合 PD-L2 表达显着更高，sPD-L2 水平显着降低。伴有狼疮性肾炎、关节痛、口腔溃疡临床表现的活动性SLE患者sPD-L2分泌相对较少。此外，这种分泌水平与补体成分 3 和 4 (C3/C4) 呈显着正相关。这些结果表明 PD-L2 可能是与 SLE 发病机制相关的有前景的生物标志物。这种分泌水平与补体成分 3 和 4 (C3/C4) 呈显着正相关。这些结果表明 PD-L2 可能是与 SLE 发病机制相关的有前景的生物标志物。这种分泌水平与补体成分 3 和 4 (C3/C4) 呈显着正相关。这些结果表明 PD-L2 可能是与 SLE 发病机制相关的有前景的生物标志物。