Quantitation of egress-independent host lysis using a 51Cr release assay. HFF monolayers were infected with either RHΔ, MBE1.1, MBE3.3, or MBD2.1 and were loaded with 51Cr. Cells were pretreated with either DMSO (a), cytochalasin D (b), or BAPTA-AM (c). A23187 was then added to all cultures, and the counts per minute (CPM) obtained from 51Cr release was measured and normalized to 104 parasitophorous vacuoles.