Lysosomes and the "toxicity" of rickettsiales. II. Non-cytocidal interactions of egg-grown C. psittaci 6BC and in vitro macrophages

Growth of Chlamydia psittaci in macrophages

Survival and growth of L-cell-cultivated Chlamydia psittaci occurred in mouse macrophages in vitro. Two major factors governing the intracellular fate of chlamydiae in macrophages are: (i) the multiplicity of infection (MOI), i.e., the elementary body (EB)-to-macrophage ratio, and (ii) the state of the EB. At a low MOI (1:1) survival and growth of live, untreated chlamydiae were optimal. The chlamydiae were internalized in macrophages within 30 to 40 min. EB proceeded to differentiate into reticulate bodies, which underwent multiplication and further matured into infectious EB in the professional phagocytic cells. In contrast, at a high MOI (100:1), survival of untreated chlamydiae was greatly reduced as a result of immediate damage to the macrophages. eb that were pretreated with heat (56 degrees C for 10 to 30 min) or coated with homologous antibody were rapidly destroyed in macrophage phagolysosomes. Fusion of ferritin-labeled lysosomes with heat-treated or opsonized EB-laden phagosomes occurred in 2 to 4 h, resulting in transfer of the ferritin marker into phagolysosomes.

Ultrastructural cytochemical evidence for the activation of lysosomes in the cytocidal effect of Chlamydia psittaci

The cytopathic effect of the polyarthritis strain of Chlamydia psittaci was studied in cultured bovine fetal spleen cells and found to be mediated by the release of lysosomal enzymes into the host cytoplasm during the late stages of chlamydial development. Ultrastructural cytochemical analysis and cell fractionation studies of infected cells revealed a close relationship between the stage of chlamydial development, fine structural features of the host, and localization of lysosomal enzyme activities. After adsorption, chlamydiae entered the host cells by endocytosis. The endocytic vacuoles containing individual chlamydiae and later the inclusion vacuoles containing the different chlamydial developmental forms were always free from lysosomal enzyme activity. Even after extensive multiplication of chlamydiae, lysosomal enzymes remained localized within lysosomes or their precursors in the host cell. Coincident with the process of chlamydial maturation, lysosomal enzymes were released into the host cytoplasm and were always associated with disintegration of host cell constituents and lysis. The chlamydiae appeared to be protected from this lysosomal enzyme activity by the inclusion membrane. After release from the inclusion, elementary bodies maintained their fine structural features, whereas all other chlamydial developmental forms lost their ultrasturctural integrity.