IFNG and infection: Because endothelial cells are important sites of R. prowazekii growth in vivo, this study first sought to determine whether IFN-γ-pretreated cultured endothelial cells would be rapidly killed by R. prowazekii. The results indicated that IFN-γ-pretreated endothelial cells were killed within hours after infection; they became permeable to trypan blue dye and to ethidium bromide, and released the intracytoplasmic enzyme lactate dehydrogenase (LDH).