Expression data of Brain CD45+ cells from WT and STI knockout mice after WNV infection

West Nile virus (WNV) is the most important cause of endemic encephalitis in the USA. Strikingly, only a small percentage of patients develop clinical disease and of these patients, approximately 1 out of 150 patients develops encephalitis. The basis for this great variability in disease outcome is unknown, but may be related to the innate immune response. Innate immune responses, critical for control of WNV infection, are initiated by signaling through pathogen recognition receptors (PRR) such as RIG-I and MDA5. IPS-1 is a key adaptor in generating a PRR-dependent interferon response.. Here we show that IPS-1 deficiency in hematopoietic cells resulted in increased mortality and delayed WNV clearance from the brain. In IPS-1-/- mice, a dysregulated immune response was detected, characterized by a massive influx of macrophages and virus-specific T cells into the infected brain. These T cells were multifunctional and were able to lyse peptide-pulsed target cells in vitro. However, virus-specific T cells in the infected IPS-1-/- brain exhibited lower functional avidity than those in C57BL/6 brains, possibly contributing to less efficient virus clearance. The presence of virus-specific memory T cells was also not protective. We also show that macrophages were increased in numbers in the IPS-1-/- brain. Both macrophages and microglia exhibited an activated phenotype. Microarray analyses showed the preferential upregulation of genes associated with leukocyte activation and inflammation. Together, these results demonstrate the critical role that hematopoietic cell expression of Type 1 interferon and other IPS-1-dependent molecules have in WNV clearance and in regulating the inflammatory response. We used 4 mice in each group. STI knockout mice developed lethath encephalitis after WNV infectin. WT mice which have mild disease after WNV were used as controls.

西尼罗河病毒（West Nile Virus, WNV）是美国地方性脑炎最主要的致病原。值得注意的是，仅少数感染者会出现临床症状，而在出现症状的患者中，约每150人中便有1人会发展为脑炎。目前这种疾病转归存在巨大差异的机制尚不明确，但推测可能与固有免疫应答相关。对于西尼罗河病毒感染防控至关重要的固有免疫应答，通过RIG-I、MDA5等病原体识别受体（pathogen recognition receptor, PRR）的信号通路启动。IPS-1是介导病原体识别受体依赖性干扰素应答的关键接头蛋白。本研究发现，造血细胞中IPS-1缺陷会导致小鼠死亡率升高，并延缓脑组织中西尼罗河病毒的清除。在IPS-1基因敲除（IPS-1-/-）小鼠体内，可检测到免疫应答失调，其特征为大量巨噬细胞与病毒特异性T细胞浸润至受感染的脑组织中。这些T细胞具备多效性功能，在体外可裂解经肽脉冲处理的靶细胞。然而，受感染的IPS-1-/-小鼠脑组织中的病毒特异性T细胞，其功能亲和力较C57BL/6小鼠脑组织中的同类细胞更低，这可能是病毒清除效率低下的原因之一。即便存在病毒特异性记忆T细胞，也未能发挥保护作用。本研究同时发现，IPS-1-/-小鼠脑组织中的巨噬细胞数量增多，且巨噬细胞与小胶质细胞均呈现激活表型。基因芯片（microarray）分析结果显示，与白细胞激活及炎症反应相关的基因呈现优先上调表达。综上，本研究结果证实，造血细胞表达的Ⅰ型干扰素（Type 1 interferon）及其他IPS-1依赖性分子，在西尼罗河病毒清除与炎症应答调控中发挥关键作用。本研究每组使用4只小鼠，STI基因敲除小鼠在感染西尼罗河病毒后会出现致死性脑炎，以感染后仅出现轻症的野生型（Wild Type, WT）小鼠作为对照。