Figure 1.

Overview of the experimental system. Initially, host cells are grown in a confluent monolayer on a plate. The cells are then covered by a layer of agar. To initiate the infection, a pipette (one mm radius) is used to carefully remove a small portion of the agar in the center of the plate. An initial inoculum of virus is then placed in the resulting hole in the agar, initiating the infection. The agar overlay serves to restrict virus propagation to nearby cells. To monitor the infection spread, monolayers are fixed at various times post-infection. The agar overlay is removed and the cells are rinsed several times, the last time with a labeled antibody that binds specifically to the viral glycoprotein. Images of the monolayers are then acquired using an inverted epifluorescent microscope.