Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
J Neuroinflammation. 2020 Sep 2;17(1):259. doi: 10.1186/s12974-020-01929-8.
Brain inflammation is a key cause of cognitive decline after central nervous system (CNS) infections. A thorough understanding of immune responses to CNS infection is essential for developing anti-inflammatory interventions that improve outcomes. Tissue-resident memory T cells (T) are non-recirculating memory T cells that provide surveillance of previously infected tissues. However, in addition to protecting the brain against reinfection, brain T can contribute to post-infectious neuroinflammation. We hypothesized that accumulation of CD8 T in the brain could be reduced by inhibiting microRNA (miR)-155, a microRNA that influences development of cytotoxic CD8 T lymphocytes during infection.
C57BL/6J mice were infected by intraperitoneal injection with a lethal inoculum of Listeria monocytogenes (Lm) then treated with antibiotics. Flow cytometry was used to quantify specific populations of brain leukocytes 28-29 days (d) post-infection (p.i.). To test the degree to which miR-155 altered leukocyte influxes into the brain, infected mice were injected with a miR-155 inhibitor or locked nucleic acid (LNA) scramble control 2d, 4d, 6d, and 8d p.i. along with antibiotic treatment. Bacterial loads in spleen and liver and body weights were measured up to 7d p.i. Brain leukocytes were analyzed 14d and 28d p.i. Confirmatory studies were performed in mutated mice lacking miR-155 (miR-155) RESULTS: Lm infection significantly increased the numbers of brain CD3CD8 lymphocytes at 28d p.i. These cells were extravascular, and displayed markers characteristic of T, with the predominant phenotype of CD44CD62LCD69CX3CR1. Further analysis showed that > 75% of brain T also expressed CD49a, PD-1, Ly6C, CD103, and CD127. Mice injected with miR-155 inhibitor lost less weight through 7d p.i. than did control mice, whereas bacterial loads in brain, liver, and spleen were not different from controls. By 28d p.i., the numbers of brain CD8 T cells were significantly decreased in mice treated with the inhibitor compared with controls. Similarly, miR-155 mice showed significantly reduced numbers of brain CD8 T cells by 28d p.i.
Brain CD8 T populations are established during neuroinvasive Lm infection. Accumulation of brain CD8 T cells is reduced by blocking miR-155 and in miR-155 mice, indicating that this molecule has a critical role in development of these specialized cells. Administering anti-miR-155 during infection could provide a novel avenue for reducing post-infectious neuroinflammation.
中枢神经系统 (CNS) 感染后，脑炎症是认知能力下降的一个关键原因。深入了解对 CNS 感染的免疫反应对于开发改善预后的抗炎干预措施至关重要。组织驻留记忆 T 细胞（T）是不循环的记忆 T 细胞，可对先前感染的组织进行监视。然而，除了保护大脑免受再感染外，脑 T 还可能导致感染后神经炎症。我们假设通过抑制 microRNA（miR）-155 可以减少大脑中 CD8 T 的积累，miR-155 是一种在感染过程中影响细胞毒性 CD8 T 淋巴细胞发育的 microRNA。
C57BL/6J 小鼠通过腹腔注射致死量李斯特菌（Lm）进行感染，然后用抗生素处理。在感染后 28-29 天（dpi），通过流式细胞术定量分析大脑白细胞的特定群体。为了测试 miR-155 改变白细胞进入大脑的程度，在感染后 2d、4d、6d 和 8d 以及抗生素治疗时，用 miR-155 抑制剂或锁核酸（LNA）对照物注射感染的小鼠。测量至感染后 7d 的脾脏和肝脏的细菌负荷和体重。在缺乏 miR-155（miR-155）的突变小鼠中进行了确认性研究。
Lm 感染显著增加了 28dpi 时大脑 CD3CD8 淋巴细胞的数量。这些细胞位于血管外，具有 T 细胞的特征性标记，主要表型为 CD44CD62LCD69CX3CR1。进一步分析表明，超过 75%的大脑 T 也表达 CD49a、PD-1、Ly6C、CD103 和 CD127。与对照组相比，注射 miR-155 抑制剂的小鼠在感染后 7d 时体重减轻幅度更小，而大脑、肝脏和脾脏中的细菌负荷与对照组无差异。在 28dpi 时，与对照组相比，用抑制剂处理的小鼠大脑中 CD8 T 细胞的数量显著减少。类似地，miR-155 小鼠在 28dpi 时大脑 CD8 T 细胞数量明显减少。
在神经侵袭性李斯特菌感染期间建立了大脑 CD8 T 群体。通过阻断 miR-155 和在 miR-155 小鼠中，大脑 CD8 T 细胞的积累减少，表明该分子在这些特化细胞的发育中具有关键作用。在感染期间给予抗 miR-155 可能为减少感染后神经炎症提供新途径。
