National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, China.
Chinese Center for Tropical Diseases Research, Shanghai, 200025, China.
Parasit Vectors. 2020 Feb 6;13(1):49. doi: 10.1186/s13071-020-3919-4.
Cystic echinococcosis is a chronic disease caused by infection with the larvae of Echinococcus granulosus. The parasite's ability to establish persistent infection is partly due to its evolving immune evasion strategies. One strategy may involve the protective effect of arginase, which impedes the control of pathogens or tumors, whereas it remains largely unknown during E. granulosus infection. Here, we analyzed whether arginase was produced in peritoneal cells and assessed its role in immunosuppression in mice infected with protoscoleces of E. granulosus.
BALB/c mice injected with protoscoleces of E. granulosus were used to evaluate the expression of arginase (ARG) in mRNA and protein levels. The profiles of ARG-1 expression in peritoneal cells and CD3ζ expression in T cells from spleens were assessed at different time points (3, 6, 9 and 12 months post-infection) by flow cytometry. In vitro, peritoneal cells were co-cultured with purified T cells in a transwell system, and the levels of CD3ζ re-expression were compared by flow cytometry. Meanwhile, the changes of L-arginine and its related metabolites in serum were tested.
Compared to the control group, the peritoneal cells from infected mice showed higher levels of ARG-1 mRNA and protein, unchanged ARG-2 and iNOS. Enhanced ARG-1 expression was present in SSCCD11bF4/80, CD11bCD11c, CD11bGr-1Ly-6CLy-6G, CD11bGr-1Ly-6CLy-6G, CD11bGr-1 and CD11bLy-6G cells. The proportion of cells and the proportion of ARG-1 expression in corresponding cells exhibited a rising trend along with the extension of infection time, except for fluctuations in SSCCD11bF4/80 and CD11bCD11c cells at 12 months post-infection, whereas the expression of CD3ζ chain in CD4 and CD8 T cells showed a descending trend. Purified T cells showed declined re-expression of CD3ζ when co-cultured with peritoneal cells from infected mice, and CD3ζ was regenerated by supplement of L-arginine or arginase inhibitor BEC, rather than NOS inhibitor L-NMMA or catalase. Meanwhile, the concentrations of L-arginine, L-citrulline and NO decreased, and those of L-ornithine and urea increased in serum post-infection.
Our findings demonstrated that ARG-1 expression is enhanced in multiple myeloid cells from peritoneum and promotes immune evasion of E. granulosus in mice by inhibiting the expression of T cell receptor CD3ζ chain and antagonism against iNOS.
包虫病是一种由细粒棘球绦虫幼虫感染引起的慢性疾病。寄生虫能够建立持续感染的部分原因是其不断进化的免疫逃避策略。一种策略可能涉及到精氨酸酶的保护作用，它阻碍了病原体或肿瘤的控制，而在细粒棘球蚴感染期间，其作用在很大程度上尚不清楚。在这里，我们分析了在感染细粒棘球蚴的原头蚴的小鼠中，腹膜细胞是否产生精氨酸酶，并评估其在免疫抑制中的作用。
用细粒棘球蚴原头蚴注射 BALB/c 小鼠，评估精氨酸酶（ARG）在 mRNA 和蛋白水平的表达。用流式细胞术在感染后 3、6、9 和 12 个月时，评估腹膜细胞中 ARG-1 表达和脾 T 细胞中 CD3ζ 表达的变化。在体外，用 Transwell 系统将腹膜细胞与纯化的 T 细胞共培养，并用流式细胞术比较 CD3ζ 再表达水平。同时，检测血清中 L-精氨酸及其相关代谢物的变化。
与对照组相比，感染小鼠的腹膜细胞中 ARG-1mRNA 和蛋白水平升高，ARG-2 和 iNOS 不变。SSCCD11bF4/80、CD11bCD11c、CD11bGr-1Ly-6CLy-6G、CD11bGr-1Ly-6CLy-6G、CD11bGr-1 和 CD11bLy-6G 细胞中存在增强的 ARG-1 表达。随着感染时间的延长，细胞比例和相应细胞中 ARG-1 表达比例呈上升趋势，但感染后 12 个月时 SSCCD11bF4/80 和 CD11bCD11c 细胞的比例出现波动，而 CD4 和 CD8 T 细胞中 CD3ζ 链的表达则呈下降趋势。当与感染小鼠的腹膜细胞共培养时，纯化的 T 细胞 CD3ζ 的再表达下降，而补充 L-精氨酸或精氨酸酶抑制剂 BEC 可使 CD3ζ 再生，而非 NOS 抑制剂 L-NMMA 或过氧化氢酶。同时，血清中 L-精氨酸、L-瓜氨酸和 NO 的浓度降低，而 L-鸟氨酸和尿素的浓度升高。
我们的研究结果表明，ARG-1 在腹膜中的多种髓样细胞中表达增强，并通过抑制 T 细胞受体 CD3ζ 链的表达和拮抗 iNOS，促进小鼠中细粒棘球蚴的免疫逃逸。
