Influence of cell culture conditions on the inhibition of herpes simplex virus type 1 replication by acyclovir.

Inhibition of herpes simplex virus type 1 (HSV-1) replication, as measured by plaque reduction by acyclovir (ACV), was studied with different cell cultures and under varying conditions. Human lung fibroblasts (HL) required much lower concentrations of ACV for inhibition of virus replication than green monkey kidney (GMK) cells. In both cell types, ACV had to be added within 7 h after infection to cause a full antiviral effect. Pretreatment of cells with ACV before infection did not increase the antiviral activity. ACV caused a stronger inhibition in HL cells which had been confluent for 4 or 7 days as compared with cells just reaching confluence. Addition of ACV and its subsequent removal caused an irreversible plaque reduction in our experiments. ACV gave a pronounced inhibition of thymidine kinase (TK)-positive HSV-1 strains. A relatively small inhibitory effect was seen with a TK-negative HSV-1 strain in HL cells, and no measurable inhibition was seen in GMK cells. Inhibition of HSV-1 replication by ACV was concluded to depend on the type of virus, the cell type used, and the condition of the cells.