Baculovirus occlusion-derived viruses (ODVs) contain ten known per os infectivity factors (PIFs). These PIFs are crucial for midgut infection of insect larvae and form, with the exception of PIF5, an ODV entry complex. Previously, R18-dequenching assays have shown that PIF3 is dispensable for binding and fusion with midgut epithelial cells. Oral infection nevertheless fails in the absence of PIF3. PIF9 has not been analysed in much depth yet. Here, the biological role of these two PIFs in midgut infection was examined by monitoring the fate of fluorescently labelled ODVs when incubated with isolated midgut cells from Spodoptera exigua larvae. Confocal microscopy showed that in the absence of either PIF3 or PIF9, the ODVs bound to the brush borders, but the nucleocapsids failed to enter the cells. Finally, we discuss how the results obtained for PIF3 with dequenching assays and confocal microscopy can be explained by a two-phase fusion process.

中文翻译：

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通过对荧光标记的病毒粒子与分离的中肠细胞之间的相互作用进行成像，对杆状病毒的渗透感染因子3和9进行功能分析。

杆状病毒闭塞衍生的病毒（ODVs）含有10已知口服感染性因子（PIFS）。这些PIF对昆虫的幼虫和肠道中肠感染至关重要，ODF进入复合体PIF5除外。以前，R18脱色测定显示PIF3对于与中肠上皮细胞结合和融合是必不可少的。然而，在没有PIF3的情况下，口腔感染会失败。尚未对PIF9进行深入分析。在这里，这两个PIF在中肠感染中的生物学作用是通过监测荧光标记的ODV与来自斜纹夜蛾（Spodoptera exigua）的中肠细胞孵育后的命运来检查的幼虫。共聚焦显微镜显示，在不存在PIF3或PIF9的情况下，ODV结合在刷状缘上，但核衣壳无法进入细胞。最后，我们讨论了如何用两相融合过程解释用去淬测定和共聚焦显微镜获得的PIF3结果。