Tick-borne encephalitis virus (TBEV) causes serious, potentially fatal neurological infections that affect humans in endemic regions of Europe and Asia. Neurons are the primary target for TBEV infection in the central nervous system. However, knowledge about this viral infection and virus-induced neuronal injury is fragmental. Here, we directly examined the pathology that occurs after TBEV infection in human primary neurons. We exploited the advantages of advanced high-pressure freezing and freeze-substitution techniques to achieve optimal preservation of infected cell architecture. Electron tomographic (ET) reconstructions elucidated high-resolution 3D images of the proliferating endoplasmic reticulum, and individual tubule-like structures of different diameters in the endoplasmic reticulum cisternae of single cells. ET revealed direct connections between the tubule-like structures and viral particles in the endoplasmic reticulum. Furthermore, ET showed connections between cellular microtubules and vacuoles that harbored the TBEV virions in neuronal extensions. This study was the first to characterize the 3D topographical organization of membranous whorls and autophagic vacuoles in TBEV-infected human neurons. The functional importance of autophagy during TBEV replication was studied in human neuroblastoma cells; stimulation of autophagy resulted in significantly increased dose-dependent TBEV production, whereas the inhibition of autophagy showed a profound, dose-dependent decrease of the yield of infectious virus.

] Institute of Parasitology Biology Centre of the Academy of Sciences of the Czech Republic Branišovská 31 CZ 37005 České Budějovice Czech Republic [2] Faculty of Science University of South Bohemia Branišovská 31 CZ 37005 České Budějovice Czech Republic

] Institute of Parasitology Biology Centre of the Academy of Sciences of the Czech Republic Branišovská 31 CZ 37005 České Budějovice Czech Republic [2] Faculty of Science University of South Bohemia Branišovská 31 CZ 37005 České Budějovice Czech Republic [3] Department of Virology Veterinary Research Institute Hudcova 70 CZ 62100 Brno Czech Republic

Department of Virology Veterinary Research Institute Hudcova 70 CZ 62100 Brno Czech Republic

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