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Rickettsia rickettsii growth and temperature-inducible protein expression in embryonic tick cell lines
P F Policastro1, U G Munderloh, E R Fischer
1Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, NIAID, NIH, Hamilton, Montana 59840, USA.
Abstract:
Rickettsia rickettsii has limited adverse effects on its arthropod vector, but causes severe disease in man. To model differences in host-parasite interaction, R. rickettsii growth and protein expression were examined at temperatures reflective of host environment in the tick cell lines DALBE3 and IDE2, the human endothelial cell line ECV304, and the African green monkey kidney cell line Vero76. At low multiplicities of infection, rickettsial titres increased 10(2)-10(3)-fold in all cell lines after incubation for 3 days at 34 degrees C. At higher multiplicities and with extended incubation, R. rickettsii showed enhanced survival in tick versus mammalian cells. No difference in rickettsial ultrastructure or protein profiles was detected between different host cell types. Rickettsial proteins of 42, 43, 48, 75 and 100 kDa are induced in tick cells shifted from 28 degrees to 34 degrees C, but not in cells maintained at 28 degrees C. This temperature response may be associated with expression of rickettsial determinants that are pathogenic to mammalian hosts.
Insights
Rickettsia rickettsii grows in tick and human cells, but survives better in tick cells. Temperature changes induce specific Rickettsia proteins, potentially linked to human disease.
Area of Science:
- Microbiology
- Cell Biology
- Pathogen-Host Interactions
Background:
- Rickettsia rickettsii causes severe human disease but has minimal impact on its tick vector.
- Understanding host-parasite interactions is crucial for modeling disease pathogenesis.
Purpose of the Study:
- To investigate Rickettsia rickettsii growth and protein expression in different host cell environments.
- To model differences in host-parasite interactions at physiologically relevant temperatures.
Main Methods:
- Culturing R. rickettsii in tick (DALBE3, IDE2) and mammalian (ECV304, Vero76) cell lines.
- Incubation at temperatures simulating host environments (28°C and 34°C).
- Analysis of rickettsial titres, ultrastructure, and protein profiles.
Main Results:
- R. rickettsii titres increased significantly in all cell lines at 34°C.
- Enhanced survival of R. rickettsii was observed in tick cells compared to mammalian cells at higher multiplicities and extended incubation.
- Specific rickettsial proteins (42, 43, 48, 75, 100 kDa) were induced in tick cells shifted to 34°C.
Conclusions:
- Temperature plays a role in R. rickettsii survival and protein expression.
- Induced proteins in tick cells at higher temperatures may be involved in mammalian pathogenesis.
- Differential survival suggests distinct host-pathogen dynamics between tick and mammalian cells.