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Requirements for ingestion of Chlamydia psittaci by mouse fibroblasts (L cells)
Abstract:
Ingestion of 14C-amino acid-labeled Chlamydia psittaci (6BC) by mouse fibroblasts (L cells) was inhibited when the host cells were incubated for 30 min at 37 degrees C in Earle salts containing 10 mug of crystalline trypsin per ml. Tryptic digestion also inhibited the ingestion of 1-mum polystrene latex beads. Trypsin-treated L cells almost completely recovered their ability to ingest chlamydiae after 4 h at 37 degrees C in medium 199 with 5% fetal calf serum. Cycloheximide (10 mug/ml) blocked this recovery. Heating 14C-amino acid-labeled C. psittaci for 3 min at 60 degrees C inhibited its ingestion by L cells, whereas inactivating it with ultraviolet light was without effect on the ingestion rate. These results show that efficient ingestion of C. psittaci by L cells involves trypsin-labile sites on the host and heat-sensitive sites on the parasite. The failure of excess unlabeled infectious C. psittaci to promote the ingestion of 14C-labeled heat-inactivated chlamydiae suggests that direct interaction between these two sites must occur for uptake to proceed normally.
Insights
Mouse fibroblasts (L cells) efficiently ingest Chlamydia psittaci through specific host cell surface sites and parasite heat-sensitive components. Recovery of this cellular uptake mechanism requires new protein synthesis.
Area of Science:
- Cell Biology
- Microbiology
- Infectious Diseases
Background:
- Chlamydia psittaci is an obligate intracellular bacterium that infects various host cells.
- Understanding the mechanisms of Chlamydia entry into host cells is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the host cell and parasite factors involved in the efficient ingestion of Chlamydia psittaci by mouse fibroblasts (L cells).
Main Methods:
- Utilized 14C-amino acid-labeled Chlamydia psittaci and L cells.
- Assessed the effect of trypsin treatment on host cell ingestion capacity.
- Investigated the role of host cell protein synthesis in recovery of ingestion.
- Examined the impact of heat and UV inactivation of Chlamydia on its ingestion.
Main Results:
- Tryptic digestion of L cells significantly inhibited Chlamydia psittaci and latex bead uptake, indicating the involvement of trypsin-labile host cell surface sites.
- Ingestion capacity was restored in trypsin-treated cells within 4 hours, but this recovery was blocked by cycloheximide, suggesting de novo protein synthesis is required.
- Heat inactivation of Chlamydia psittaci reduced its ingestion, while UV inactivation had no effect, pointing to heat-sensitive parasite components.
Conclusions:
- Efficient Chlamydia psittaci ingestion by L cells depends on specific trypsin-labile sites on the host cell and heat-sensitive sites on the bacterium.
- The interaction between these sites is direct and essential for normal uptake.
- Host cell protein synthesis is necessary for restoring the cellular machinery involved in Chlamydia ingestion.