FIG. 4.

SPs prevent cell-to-cell spread. From 500 to 1,000 infected cells (harvested at 4 to 5 h postinfection) were plated onto duplicate monolayers of uninfected cells in medium containing pooled human IgG (Sigma) in the presence of an SP or control buffer, and the number of plaques formed were counted following immunostaining 48 h later. The results are presented as the PFU formed in the presence of each drug as a percentage of the PFU formed in the presence of control medium, and each value is the mean ± standard deviation obtained from at least two independent experiments conducted in duplicate (A). Representative plaques viewed under ×100 (B and C) or ×200 (D and E) magnification are shown.