Compound D7 reduces the number and infectivity of C. pneumoniae progeny. HeLa cells were infected with C. pneumoniae (MOI of 5) and MEM containing either DMSO (0.1%) or D7 (10 μM) was added at 1 hpi. Cells were lysed at 72 hpi and chlamydial lysates diluted 10-1 and 10-2 and used to infect fresh HeLa cell monolayers. Infected cells were then incubated for 72 hours in MEM (without D7 or DMSO) and inclusions were stained with FITC-conjugated anti-LPS monoclonal antibody. C. pneumoniae harvested from DMSO-exposed HeLa cells produced many inclusions of normal size upon subsequent passage (top panels; dilution of passage indicated). A substantial reduction in both the number and size of inclusions was seen with chlamydiae harvested from HeLa cells exposed to compound D7 (bottom panels). Similar results were obtained with undiluted chlamydial lysates and with lysates harvested at 84 hpi (data not shown).