Lucas Tiffany M, Richner Justin M, Diamond Michael S
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA Department of Pathology & Immunology, Washington University School of Medicine, St. Louis, Missouri, USA Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA The Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, Missouri, USA
J Virol. 2015 Dec 23;90(5):2600-15. doi: 10.1128/JVI.02463-15.
The mammalian host responds to viral infections by inducing expression of hundreds of interferon-stimulated genes (ISGs). While the functional significance of many ISGs has yet to be determined, their cell type and temporal nature of expression suggest unique activities against specific pathogens. Using a combination of ectopic expression and gene silencing approaches in cell culture, we previously identified Ifi27l2a as a candidate antiviral ISG within neuronal subsets of the central nervous system (CNS) that restricts infection by West Nile virus (WNV), an encephalitic flavivirus of global concern. To investigate the physiological relevance of Ifi27l2a in the context of viral infection, we generated Ifi27l2a(-/-) mice. Although adult mice lacking Ifi27l2a were more vulnerable to lethal WNV infection, the viral burden was greater only within the CNS, particularly in the brain stem, cerebellum, and spinal cord. Within neurons of the cerebellum and brain stem, in the context of WNV infection, a deficiency of Ifi27l2a was associated with less cell death, which likely contributed to sustained viral replication and higher titers in these regions. Infection studies in a primary cell culture revealed that Ifi27l2a(-/-) cerebellar granule cell neurons and macrophages but not cerebral cortical neurons, embryonic fibroblasts, or dendritic cells sustained higher levels of WNV infection than wild-type cells and that this difference was greater under conditions of beta interferon (IFN-β) pretreatment. Collectively, these findings suggest that Ifi27l2a has an antiviral phenotype in subsets of cells and that at least some ISGs have specific inhibitory functions in restricted tissues.
The interferon-stimulated Ifi27l2a gene is expressed differentially within the central nervous system upon interferon stimulation or viral infection. Prior studies in cell culture suggested an antiviral role for Ifi27l2a during infection by West Nile virus (WNV). To characterize its antiviral activity in vivo, we generated mice with a targeted gene deletion of Ifi27l2a. Based on extensive virological analyses, we determined that Ifi27l2a protects mice from WNV-induced mortality by contributing to the control of infection of the hindbrain and spinal cord, possibly by regulating cell death of neurons. This antiviral activity was validated in granule cell neurons derived from the cerebellum and in macrophages but was not observed in other cell types. Collectively, these data suggest that Ifi27l2a contributes to innate immune restriction of WNV in a cell-type- and tissue-specific manner.
哺乳动物宿主通过诱导数百种干扰素刺激基因（ISG）的表达来应对病毒感染。虽然许多ISG的功能意义尚未确定，但其细胞类型和表达的时间特性表明它们针对特定病原体具有独特的活性。我们先前在细胞培养中结合异位表达和基因沉默方法，在中枢神经系统（CNS）的神经元亚群中鉴定出Ifi27l2a作为候选抗病毒ISG，它可限制西尼罗河病毒（WNV）的感染，WNV是一种引起全球关注的脑炎黄病毒。为了研究Ifi27l2a在病毒感染背景下的生理相关性，我们培育了Ifi27l2a基因敲除小鼠。尽管缺乏Ifi27l2a的成年小鼠更容易受到致命性WNV感染，但病毒载量仅在中枢神经系统内更高，特别是在脑干、小脑和脊髓中。在WNV感染的情况下，在小脑和脑干的神经元中，Ifi27l2a的缺乏与较少的细胞死亡相关，这可能导致这些区域持续的病毒复制和更高的病毒滴度。原代细胞培养中的感染研究表明，Ifi27l2a基因敲除的小脑颗粒细胞神经元和巨噬细胞，但不是大脑皮层神经元、胚胎成纤维细胞或树突状细胞，比野生型细胞维持更高水平 的WNV感染，并且在β干扰素（IFN-β）预处理的条件下这种差异更大。总的来说，这些发现表明Ifi27l2a在细胞亚群中具有抗病毒表型，并且至少一些ISG在受限组织中具有特定的抑制功能。
干扰素刺激的Ifi27l2a基因在干扰素刺激或病毒感染后在中枢神经系统内差异表达。先前在细胞培养中的研究表明Ifi27l2a在西尼罗河病毒（WNV）感染期间具有抗病毒作用。为了表征其在体内的抗病毒活性，我们培育了Ifi27l2a基因靶向缺失的小鼠。基于广泛的病毒学分析，我们确定Ifi27l2a通过有助于控制后脑和脊髓的感染来保护小鼠免受WNV诱导的死亡，可能是通过调节神经元的细胞死亡。这种抗病毒活性在源自小脑的颗粒细胞神经元和巨噬细胞中得到验证，但在其他细胞类型中未观察到。总的来说，这些数据表明Ifi27l2a以细胞类型和组织特异性方式对WNV的先天免疫限制做出贡献。
