DataSheet_1_Distinct Role of TNFR1 and TNFR2 in Protective Immunity Against Orientia tsutsugamushi Infection in Mice.docx

Infection with Orientia tsutsugamushi, an obligate intracellular bacterium, can cause mild or severe scrub typhus. Some patients develop acute lung injury, multi-organ failure, and fatal infection; however, little is known regarding key immune mediators that mediate infection control or disease pathogenesis. Using murine models of scrub typhus, we demonstrated in this study the requirement of TNF-TNFR signaling in protective immunity against this infection. Mice lacking both TNF receptors (TNFR1 and TNFR2) were highly susceptible to O. tsutsugamushi infection, displaying significantly increased tissue bacterial burdens and succumbing to infection by day 9, while most wild-type mice survived through day 20. This increased susceptibility correlated with poor activation of cellular immunity in inflamed tissues. Flow cytometry of lung- and spleen-derived cells revealed profound deficiencies in total numbers and activation status of NK cells, neutrophils, and macrophages, as well as CD4 and CD8 T cells. To define the role of individual receptors in O. tsutsugamushi infection, we used mice lacking either TNFR1 or TNFR2. While deficiency in either receptor alone was sufficient to increase host susceptibility to the infection, TNFR1 and TNFR2 played a distinct role in cellular responses. TNF signaling through TNFR1 promoted inflammatory responses and effector T cell expansion, while TNFR2 signaling was associated with anti-inflammatory action and tissue homeostasis. Moreover, TNFRs played an intrinsic role in CD8+ T cell activation, revealing an indispensable role of TNF in protective immunity against O. tsutsugamushi infection.

专性胞内菌恙虫病东方体（Orientia tsutsugamushi）感染可引发轻症或重症恙虫病（scrub typhus）。部分患者会出现急性肺损伤、多器官衰竭甚至致死性感染，但目前对于介导感染控制或疾病发病机制的关键免疫介质仍知之甚少。本研究利用恙虫病小鼠模型，证实了肿瘤坏死因子-肿瘤坏死因子受体（Tumor Necrosis Factor-Tumor Necrosis Factor Receptor, TNF-TNFR）信号通路在对抗该感染的保护性免疫中的必要性。同时缺失两种肿瘤坏死因子受体（TNFR1与TNFR2）的小鼠对恙虫病东方体感染极易易感，其组织细菌载量显著升高，并于感染后第9天全部死亡，而多数野生型小鼠可存活至第20天。这种易感性升高与炎症组织内细胞免疫激活不足密切相关。对肺脏与脾脏来源细胞的流式细胞术（flow cytometry）分析显示，自然杀伤细胞（NK cells）、中性粒细胞、巨噬细胞以及CD4、CD8 T细胞的总数与激活状态均存在显著缺陷。为明确单一受体在恙虫病东方体感染中的作用，本研究使用了仅缺失TNFR1或仅缺失TNFR2的小鼠。尽管仅缺失任一受体即可升高宿主对感染的易感性，但TNFR1与TNFR2在细胞应答中发挥的作用截然不同。通过TNFR1介导的肿瘤坏死因子（Tumor Necrosis Factor, TNF）信号可促进炎症应答与效应T细胞扩增，而TNFR2信号则与抗炎作用及组织稳态维持相关。此外，TNFR在CD8+ T细胞激活中发挥固有作用，这揭示了TNF在对抗恙虫病东方体感染的保护性免疫中不可或缺的地位。