*4.1. Viruses and Cell Cultures*

The RNA-containing tick-borne encephalitis virus (TBEV) strain Dal'negorsk that was isolated in 1973 from the brain of a patient with a fatal outcome of TBE, and characterized as a Far Eastern subtype, was used (Gene Bank Whole Genome Sequence Number: FJ402886) [29]. The DNA-containing herpes virus (HSV-1, strain VR3) was obtained from the National Collection of US Viruses (Rockville, MD, USA).

TBEV was grown on the pig embryo kidney (PK) cells using medium 199 supplemented with 10% fetal bovine serum (FBS) and 100 U/mL gentamicin. HSV-1 was grown in African green monkey kidney (Vero) cells using Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% FBS, gentamicin, and glutamine.

Viral titers were determined by cytopathic effect (CPE) assay and expressed as the 50% tissue culture infectious dose (TCID50/mL). The TBEV titer was 108.8 TCID50/mL, and the titer of HSV-1 was 108.25 TCID50/mL.
