ICP0-deficient HSV is able to form replication compartments in cells harbouring quiescent KM110-R. Confluent monolayers of HEL growing on coverslips were mock infected (not shown) or infected with 6 PFU/cell of KM110-R to establish quiescence. Four days later the cells were either mock infected or superinfected with 30 PFU/cell of n212 or 10 PFU/cell KOS (not shown) in the presence or absence of 400 μg/mL PAA. 9.5 hours later the cells were fixed and processed for visualization of ICP4 by indirect immunofluorescence. Nuclei were counter-stained with Hoescht 33342. Representative fields of cells harbouring KM110-R are shown following mock-infection or infection with n212 in the presence and absence of PAA.