FIG. 5.

Effect of endosomal cysteine protease inhibitors on infectivity of RA59_EGFP and RA59/MHV-2S_EGFP in L2 cells. Cells were pretreated with various concentrations of protease inhibitors E-64 (cysteine protease inhibitor) (A), CA-074 (specific cathepsin B inhibitor) (B), and Z-FY-DMK (cathepsin L/B inhibitor) (C) for 3 h before adding serially diluted EGFP-expressing viruses. After 1 h of adsorption, the viral inocula were removed and the cells were incubated with medium containing the same drug for another hour. The cells were then incubated with fresh growth medium without drugs, and infectivity was measured at 8 h postinfection by counting EGFP-positive cells. Infectivity values are reported as infectivity units (iu)/ml virus, where one infectivity unit corresponds to one EGFP-positive cell. Infectivity of EGFP-expressing viruses in the presence of inhibitors was expressed as a percentage of infectivity observed in mock-treated cells. Error bars represent the standard deviations from at least three replicates.