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Penetration of cultured mouse fibroblasts (L cells) by Rickettsia prowazeki
Abstract:
The association of Rickettsia prowazeki with L cells was examined by using a novel radioactive assay in which [alpha-(32)P]ATP-labeled rickettsiae were incubated with L-cell monolayers. Rickettsial association with the monolayer involved adherence and internalization steps that could be experimentally distinguished. Since R. prowazeki but not L cells possess an ATP-ADP obligate exchange transport system, addition of excess unlabeled ATP resulted in exchange of the labeled ATP from external, adherent rickettsiae but not from internalized rickettsiae. Rickettsial association was temperature dependent and was a linear function of both time and concentration. More than 90% of the biologically active rickettsiae associated with L cells was internalized. Rickettsial internalization required active participation of both rickettsiae and L cells; inactivation of either greatly reduced internalization. Rickettsial adherence to poisoned L cells was a saturable function of time and concentration. Adherence showed less temperature dependence than did internalization, but like rickettsial internalization, the extent of adherence was extremely low at 0 degrees C. The rate and extent of adherence by inactivated and native rickettsiae to inactivated L cells were similar. Although inactive rickettsiae adhered to active and inactive L cells to a similar extent, inactive rickettsiae were internalized poorly by active L cells. These data form the basis for the hypothesis that R. prowazeki are internalized by the host cell through a process of "induced phagocytosis" and that inactivated rickettsiae adhere to the host cell differently from native rickettsiae, failing to trigger the endocytosis mechanism.
Insights
Rickettsia prowazeki actively infects L cells through induced phagocytosis. This process requires both viable bacteria and host cells, with over 90% of associated bacteria being internalized.
Area of Science:
- Cell Biology
- Microbiology
- Infectious Diseases
Background:
- Rickettsia prowazeki is an obligate intracellular bacterium.
- Understanding the mechanism of Rickettsia entry into host cells is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the adherence and internalization mechanisms of Rickettsia prowazeki in L cells.
- To differentiate between bacterial adherence and host cell entry processes.
Main Methods:
- Utilized a novel radioactive assay with [alpha-(32)P]ATP-labeled Rickettsia prowazeki.
- Incubated labeled bacteria with L-cell monolayers at varying temperatures, times, and concentrations.
- Used unlabeled ATP to distinguish between external and internalized bacteria based on their ATP-ADP exchange transport system.
Main Results:
- Rickettsial association with L cells involves distinct adherence and internalization steps.
- Internalization is temperature-dependent, requiring active participation from both bacteria and host cells.
- Over 90% of biologically active Rickettsia were internalized, suggesting an active host cell process.
Conclusions:
- Rickettsia prowazeki is internalized by host cells via a process termed "induced phagocytosis".
- Inactive Rickettsia adhere differently, failing to trigger the endocytosis mechanism, highlighting the importance of bacterial viability in infection.