FIG. 4.

Three MHV growth experiments in which serum-free culture medium was substituted for serum-containing culture medium at different points during incubation of R9F2-PMO with DBT cells or virus growth period were performed. Cells were treated in 1 ml of VP-SFM, and then 10 ml of serum-containing medium was added after 3 h (left panel) or 6 h (middle panel). One treatment group received 10 ml of VP-SFM after inoculation (right panel). Results are presented for a minimum of three replicate flasks per treatment, and cells were inoculated with MHV after 6 h of R9F2-PMO treatment. Infectious MHV present in culture supernatant recovered 18 h after inoculation was titrated by plaque assay. Mean titers in PFU per milliliter are shown with error bars corresponding to the standard errors of the means. An MHV growth experiment was performed with incubation in the absence of serum. Results shown are mean values of three replicate flasks in one of four independent assays, with standard errors indicated by error bars.