Herpes simplex virus type 1 (HSV-1, strain KOS) was obtained from the strain collection of the Consiliar and Reference Center for Alpha Herpes Virus Infection, Institute of Virology and Antiviral Therapy, University Jena, Germany and propagated in Vero cells. The virus infected cells were frozen and thawed and the virus suspension was titrated on Vero cells and stored at À70 C (7).