Chlamydia psittaci elementary body envelopes: ingestion and inhibition of phagolysosome fusion

The cell surface of Chlamydia psittaci seems important for establishing infection since (i) UV-treated elementary bodies (EB) attach to and are ingested by L cells and (ii) heat or antibody treatment decreases attachment to L cells and promotes the fusion of chlamydiae-containing phagosomes with lysosomes in macrophages. In the studies reported here, [3H]uridine-labeled UV-treated EB also persisted in mouse resident peritoneal macrophages and L cells, suggesting that phagosome-lysosome fusion is inhibited. We therefore chose to investigate the ingestion and internal fate of isolated purified EB envelopes in both nonprofessional and professional phagocytic cells. EB envelopes are internalized by target host cells as efficiently as are whole EB. Transmission electron microscopy of macrophages whose lysosomes were marked with ferritin revealed the persistence of individual envelopes in phagosomes devoid of ferritin for the 3-h observation period. In contrast, EB envelopes heated to 56 degrees C for 15 min were consistently found in ferritin-labeled phagolysosomes as early as 30 min. As another index of persistence, isolated EB envelopes were radioisotopically labeled with a Bolton-Hunter analog, [3H]N-succinimidyl propionate, and their fate as trichloroacetic acid-precipitable material was followed. A third probe, employed to detect the persistence of non-biodegradable antigen, was indirect immunofluorescence. Fluorescein-positive antigens were brightly visible for 7 days in both macrophages and L cells when they were inoculated with untreated EB or EB maintained in penicillin. But L cells inoculated with EB envelopes or EB treated with UV or chloramphenicol, all of which prevent the conversion of infectious EB into the metabolically active reticulate bodies, displayed reduced internal fluorescence by 2 days and the appearance of fluorescent material on the cell surface. This release of EB envelope material occurred in the absence of phagolysosome fusion. The data add credence to the belief that the spontaneous breakdown or autolytic enzyme release of EB envelope components must occur preparatory to the conversion of EB to reticulate bodies.