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Growth of Chlamydia psittaci in macrophages
Abstract:
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.
Insights
Chlamydia psittaci survives and grows in mouse macrophages at low infection doses. High doses or pretreated elementary bodies (EB) lead to macrophage damage or destruction, impacting chlamydial fate.
Area of Science:
- Microbiology
- Cell Biology
- Immunology
Background:
- Chlamydia psittaci is an obligate intracellular bacterium.
- Macrophages are key immune cells involved in pathogen clearance.
- The intracellular survival of Chlamydia is critical for its pathogenesis.
Purpose of the Study:
- To investigate the factors influencing the intracellular survival and growth of Chlamydia psittaci in mouse macrophages.
- To determine the impact of multiplicity of infection (MOI) and elementary body (EB) state on chlamydial fate within macrophages.
Main Methods:
- In vitro cultivation of Chlamydia psittaci in L-cells.
- Infection of mouse macrophages with varying MOI of C. psittaci.
- Treatment of EBs with heat or homologous antibody prior to infection.
- Observation of EB internalization, differentiation, and replication within macrophages.
- Analysis of macrophage damage and lysosome-phagosome fusion using ferritin labeling.
Main Results:
- Optimal survival and growth of live, untreated C. psittaci occurred at a low MOI (1:1), with internalization and differentiation into reticulate bodies within 30-40 minutes.
- High MOI (100:1) significantly reduced chlamydial survival due to immediate macrophage damage.
- Heat- or antibody-treated EBs were rapidly destroyed within macrophage phagolysosomes.
- Lysosome fusion with EB-laden phagosomes occurred within 2-4 hours for treated EBs.
Conclusions:
- The multiplicity of infection and the state of the elementary body are critical determinants of Chlamydia psittaci's intracellular fate in macrophages.
- Low MOI supports C. psittaci replication, while high MOI or pre-treated EBs lead to bacterial destruction and/or host cell damage.
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