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Interactions between Rickettsia prowazekii and rabbit polymorphonuclear leukocytes: rickettsiacidal and leukotoxic
Abstract:
Rickettsia prowazekii was assessed for in vitro susceptibility to phagocytosis by rabbit polymorphonuclear leukocytes. [alpha-32P]adenosine triphosphate-labeled rickettsiae were used to determine phagocytosis and adsorption quantitatively. R. prowazekii was less susceptible to phagocytosis than were Escherichia coli and Neisseria gonorrhoeae. Although R. prowazekii was similar to E. coli in susceptibility to superoxide and activated halide, few phagocytized rickettsial cells were inactivated after being ingested by polymorphonuclear leukocytes, and rickettsiae were observed free in polymorphonuclear leukocyte cytoplasm. At low ratios of rickettsiae to polymorphonuclear leukocytes, PMN phagocytosis increased as a linear function of time, but at high ratios (multiplicity of infection, 50) rickettsiae were phagocytized during only the first 10 min of incubation. Polymorphonuclear leukocytes were damaged in the presence of high rickettsial multiplicities such that they released lactate dehydrogenase into the medium and lost the ability to phagocytize both rickettsiae and E. coli. The amount of leukotoxic activity in a given rickettsial sample correlated with the relative hemolytic activity of that sample. The rickettsial leukotoxin was probably not a soluble product, was active in the absence of phagocytosis, and was inhibited by inactivation of the rickettsiae or by incubation at 4 degrees C.
Insights
Rickettsia prowazekii resists phagocytosis by immune cells, surviving within them and damaging host cells. This study reveals insights into the bacterium's survival mechanisms and its leukotoxic effects.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Polymorphonuclear leukocytes (PMNs) are crucial for innate immunity against bacterial pathogens.
- Understanding bacterial evasion mechanisms is vital for developing effective treatments.
Purpose of the Study:
- To investigate the in vitro susceptibility of Rickettsia prowazekii to phagocytosis by rabbit PMNs.
- To characterize the interaction between R. prowazekii and PMNs, including bacterial survival and host cell damage.
Main Methods:
- Quantitative assessment of phagocytosis using radiolabeled R. prowazekii.
- Comparison of phagocytosis rates with Escherichia coli and Neisseria gonorrhoeae.
- Evaluation of PMN damage and leukotoxic activity.
Main Results:
- R. prowazekii exhibited lower susceptibility to phagocytosis than E. coli and N. gonorrhoeae.
- Phagocytized R. prowazekii cells were often not inactivated and were found within PMN cytoplasm.
- High multiplicities of R. prowazekii caused PMN damage, lactate dehydrogenase release, and loss of phagocytic capacity.
- Leukotoxic activity correlated with hemolytic activity and was likely cell-associated.
Conclusions:
- R. prowazekii effectively evades phagocytic clearance by PMNs.
- The bacterium possesses leukotoxic properties that impair immune cell function.
- These findings highlight R. prowazekii's mechanisms for host immune system evasion.