Kim Seong Bum, Choi Jin Young, Uyangaa Erdenebileg, Patil Ajit Mahadev, Hossain Ferdaus Mohd Altaf, Hur Jin, Park Sang-Youel, Lee John-Hwa, Kim Koanhoi, Eo Seong Kug
College of Veterinary Medicine and Bio-Safety Research Institute, Chonbuk National University, Iksan, 54596, Republic of Korea.
Department of Bioactive Material Sciences, Graduate School, Chonbuk National University, Jeonju, 54896, Republic of Korea.
J Neuroinflammation. 2016 Apr 18;13(1):79. doi: 10.1186/s12974-016-0551-5.
Japanese encephalitis (JE), a leading cause of viral encephalitis, is characterized by extensive neuroinflammation following infection with neurotropic JE virus (JEV). Indoleamine 2,3-dioxygenase (IDO) has been identified as an enzyme associated with immunoregulatory function. Although the regulatory role of IDO in viral replication has been postulated, the in vivo role of IDO activity has not been fully addressed in neurotropic virus-caused encephalitis.
Mice in which IDO activity was inhibited by genetic ablation or using a specific inhibitor were examined for mortality and clinical signs after infection. Neuroinflammation was evaluated by central nervous system (CNS) infiltration of leukocytes and cytokine expression. IDO expression, viral burden, JEV-specific T-cell, and type I/II interferon (IFN-I/II) innate responses were also analyzed.
Elevated expression of IDO activity in myeloid and neuron cells of the lymphoid and CNS tissues was closely associated with clinical signs of JE. Furthermore, inhibition of IDO activity enhanced resistance to JE, reduced the viral burden in lymphoid and CNS tissues, and resulted in early and increased CNS infiltration by Ly-6C(hi) monocytes, NK, CD4(+), and CD8(+) T-cells. JE amelioration in IDO-ablated mice was also associated with enhanced NK and JEV-specific T-cell responses. More interestingly, IDO ablation induced rapid enhancement of type I IFN (IFN-I) innate responses in CD11c(+) dendritic cells (DCs), including conventional and plasmacytoid DCs, following JEV infection. This enhanced IFN-I innate response in IDO-ablated CD11c(+) DCs was coupled with strong induction of PRRs (RIG-I, MDA5), transcription factors (IRF7, STAT1), and antiviral ISG genes (Mx1, Mx2, ISG49, ISG54, ISG56). IDO ablation also enhanced the IFN-I innate response in neuron cells, which may delay the spread of virus in the CNS. Finally, we identified that IDO ablation in myeloid cells derived from hematopoietic stem cells (HSCs) dominantly contributed to JE amelioration and that HSC-derived leukocytes played a key role in the enhanced IFN-I innate responses in the IDO-ablated environment.
Inhibition of IDO activity ameliorated JE via enhancement of antiviral IFN-I/II innate and adaptive T-cell responses and increased CNS infiltration of peripheral leukocytes. Therefore, our data provide valuable insight into the use of IDO inhibition by specific inhibitors as a promising tool for therapeutic and prophylactic strategies against viral encephalitis caused by neurotropic viruses.
日本脑炎（JE）是病毒性脑炎的主要病因，其特征是感染嗜神经性日本脑炎病毒（JEV）后发生广泛的神经炎症。吲哚胺2,3-双加氧酶（IDO）已被确定为一种与免疫调节功能相关的酶。尽管已推测IDO在病毒复制中具有调节作用，但IDO活性在嗜神经性病毒引起的脑炎中的体内作用尚未得到充分研究。
通过基因敲除或使用特异性抑制剂抑制IDO活性的小鼠，在感染后检测其死亡率和临床症状。通过白细胞在中枢神经系统（CNS）的浸润和细胞因子表达来评估神经炎症。还分析了IDO表达、病毒载量、JEV特异性T细胞以及I/II型干扰素（IFN-I/II）固有免疫反应。
淋巴组织和CNS组织的髓样细胞和神经元细胞中IDO活性的升高表达与JE的临床症状密切相关。此外，抑制IDO活性可增强对JE的抵抗力，降低淋巴组织和CNS组织中的病毒载量，并导致Ly-6C(hi)单核细胞、NK细胞、CD4(+)和CD8(+) T细胞早期且增加地浸润CNS。IDO基因敲除小鼠中JE的改善还与NK细胞和JEV特异性T细胞反应增强有关。更有趣的是，IDO基因敲除在JEV感染后诱导CD11c(+)树突状细胞（DCs），包括传统DCs和浆细胞样DCs中I型干扰素（IFN-I）固有免疫反应迅速增强。IDO基因敲除的CD11c(+) DCs中这种增强的IFN-I固有免疫反应与PRRs（RIG-I、MDA5）、转录因子（IRF7、STAT1）和抗病毒ISG基因（Mx1、Mx2、ISG49、ISG54、ISG56）的强烈诱导相关。IDO基因敲除还增强了神经元细胞中的IFN-I固有免疫反应，这可能会延迟病毒在CNS中的传播。最后，我们确定造血干细胞（HSCs）来源的髓样细胞中的IDO基因敲除对JE的改善起主要作用，并且HSC来源的白细胞在IDO基因敲除环境中增强的IFN-I固有免疫反应中起关键作用。
抑制IDO活性通过增强抗病毒IFN-I/II固有免疫和适应性T细胞反应以及增加外周白细胞向CNS的浸润来改善JE。因此，我们的数据为使用特异性抑制剂抑制IDO作为针对嗜神经性病毒引起的病毒性脑炎的治疗和预防策略的有前景工具提供了有价值的见解。
