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Effects of Corynebacterium parvum on Escherichia coli infection in mice
Abstract:
The contribution of activated macrophages to protection against Escherichia coli was studied in mice. Mice treated intraperitoneally with killed Corynebacterium parvum organisms 1 d prior to challenge showed an increased resistance to intraperitoneal infection with E. coli; the predominant leucocytes in the peritoneal cavity of these animals were polymorphonuclear cells. However, treatment with C. parvum 4 d prior to challenge induced mainly activated macrophages in the peritoneal cavity and host resistance to the infection was not increased. Activated macrophages from such mice showed both enhanced phagocytic activity in vivo and a high degree of intracellular killing of E. coli in vitro. At the same time these cells became more susceptible to the cytotoxic effect of endotoxin. After challenge with E. coli there was a marked decrease in the number of peritoneal macrophages in mice that were treated with C. parvum 4 d prior to challenge. Increased susceptibility of activated macrophages to the cytotoxic effect of endotoxin could explain the absence of enhanced resistance to E. coli infection in such animals.
Insights
Activated macrophages did not enhance protection against Escherichia coli infection in mice. This was linked to their increased susceptibility to endotoxin, leading to a decrease in macrophage numbers post-infection.
Area of Science:
- Immunology
- Microbiology
Background:
- Activated macrophages play a role in host defense.
- Understanding their specific contributions to bacterial infection is crucial.
Purpose of the Study:
- To investigate the role of activated macrophages in protection against Escherichia coli infection in mice.
- To determine the impact of Corynebacterium parvum treatment timing on macrophage activation and host resistance.
Main Methods:
- Mice were treated with Corynebacterium parvum at different time points (1 day or 4 days) before challenge with Escherichia coli.
- Peritoneal lavage was performed to analyze leukocyte populations (polymorphonuclear cells and macrophages).
- In vivo phagocytic activity and in vitro intracellular killing of E. coli by macrophages were assessed.
Main Results:
- Treatment 1 day prior to challenge increased resistance, with polymorphonuclear cells predominating.
- Treatment 4 days prior to challenge induced activated macrophages but did not increase resistance.
- Activated macrophages showed enhanced phagocytosis and killing of E. coli but increased susceptibility to endotoxin.
- A decrease in peritoneal macrophages was observed after E. coli challenge in mice treated 4 days prior.
Conclusions:
- Activated macrophages, while possessing enhanced antimicrobial functions, may not confer protection against E. coli when susceptible to endotoxin.
- The timing of macrophage activation is critical for effective host defense against E. coli infection.