Department of Biology, Wilfrid Laurier University, 75 University Ave W, Waterloo, Ontario N2L 3C5, Canada.
Department of Health Sciences, Wilfrid Laurier University, 75 University Ave W, Waterloo, Ontario N2L 3C5, Canada.
Virus Res. 2017 Jun 15;238:114-123. doi: 10.1016/j.virusres.2017.06.008. Epub 2017 Jun 17.
Frog virus 3 is the type species of the Ranavirus genus and the causative agent of massive mortalities of aquatic species worldwide. A critical step in limiting virus replication, particularly early in infection, is the innate immune response. Presently, little is known regarding what innate immune strategies limit FV3 at the cellular level. To this end, the present study uses two rainbow trout cell lines, RTG-2 and RTgutGC, which demonstrate susceptible and relatively resistant phenotypes to FV3 infection, to elucidate susceptibility factors to FV3. RTG-2 demonstrated a lower LD and significantly higher virus transcript production compared to RTgutGC. The mode of cell death appeared to be apoptosis for both cell lines; however, RTG-2 did not demonstrate fragmented nuclei typical of apoptosis in cell culture. Next, the source of RTG-2's enhanced susceptibility was pursued, in hopes of highlighting unique features of this virus-host interaction that would predispose a cell to susceptibility. The type I interferon (IFN) response is the keystone mechanism used by the innate immune system to limit virus replication. FV3 induced very low to no levels of IFNs and interferon stimulated genes (ISGs) in either cell line, nor did inducing IFNs prior to infection inhibit virus-induced cell death. A dsRNA-induced antiviral state did reduce virus replication however. UV-inactivated FV3 was also able to kill RTG-2; thus, susceptibility to FV3-induced cell death observed in RTG-2 was independent of virus replication or the cell's ability, or lack thereof, to produce an IFN response. Importantly, RTG-2 showed greater viral entry compared to RTgutGC, suggesting non-innate immune factors, such as surface receptor expression or endocytic mechanism rates, may be key contributors to FV3 susceptibility. These findings contribute to our understanding of cell-level susceptibility to this environmentally important aquatic animal pathogen.
蛙病毒 3 是蛙病毒属的模式种，也是导致全球水生物种大规模死亡的病原体。先天免疫反应是限制病毒复制的关键步骤，特别是在感染早期。目前，对于先天免疫策略如何在细胞水平上限制 FV3 的了解甚少。为此，本研究使用两种虹鳟鱼细胞系 RTG-2 和 RTgutGC，它们对 FV3 感染表现出易感和相对抗性表型，以阐明对 FV3 的易感性因素。RTG-2 的 LD 较低，病毒转录产物明显高于 RTgutGC。两种细胞系的细胞死亡方式似乎都是凋亡；然而，RTG-2 的细胞核没有出现典型的细胞培养中凋亡的碎片化。接下来，研究了 RTG-2 易感性增强的来源，希望能突出这种病毒-宿主相互作用的独特特征，使细胞易感性增强。I 型干扰素（IFN）反应是先天免疫系统限制病毒复制的关键机制。FV3 在两种细胞系中诱导的 IFN 水平非常低或检测不到，IFN 诱导也不能抑制感染前病毒诱导的细胞死亡。dsRNA 诱导的抗病毒状态确实减少了病毒复制，但 UV 失活的 FV3 也能杀死 RTG-2；因此，在 RTG-2 中观察到的对 FV3 诱导的细胞死亡的易感性与病毒复制或细胞产生 IFN 反应的能力或缺乏无关。重要的是，RTG-2 显示出比 RTgutGC 更高的病毒进入能力，这表明非先天免疫因素，如表面受体表达或内吞机制速率，可能是 FV3 易感性的关键因素。这些发现有助于我们了解细胞水平对这种具有重要环境意义的水生动物病原体的易感性。
