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Bactericidal activity of alveolar and peritoneal macrophages exposed in vitro to three strains of Pasteurella
Abstract:
Normal ICR mice were infected intravenously, intraperitoneally, or aerogenically with Pasteurella multocida strains isolated from a turkey (S68), calf (V90), or rabbit (J20) lung. Both the turkey and calf isolates were highly virulent for mice and multiplied logarithmically in the lungs, liver, and spleen, resulting in death of the animals in 18 to 36 h. The rabbit strain was avirulent for mice, but repeated passage in mice did result in some increased virulence. All three strains of P. multocida were inactivated rapidly by normal mouse peritoneal macrophages, provided that the organisms were opsonized with specific hyperimmune serum before being exposed to the macrophage monolayers. P. multocida was slowly inactivated by normal mouse alveolar macrophages when the organisms were preopsonized. However, the surviving organisms later multiplied extensively in vitro. Macrophages harvested from hyperimmunized mice were no better at inactivating opsonized P. multocida cells than were normal mouse cells. The relative importance of the different phagocytic cell populations in the uptake and killing of opsonized P. multocida cells is discussed in relation to immunity to this important animal pathogen.
Insights
Virulent Pasteurella multocida strains caused rapid death in mice. Opsonization with serum enhanced macrophage inactivation of P. multocida, but alveolar macrophages showed limited effectiveness.
Area of Science:
- Veterinary Microbiology
- Immunology
- Infectious Diseases
Background:
- Pasteurella multocida is a significant animal pathogen causing respiratory infections.
- Understanding host-pathogen interactions and immune responses is crucial for controlling P. multocida infections.
Purpose of the Study:
- To investigate the virulence of different P. multocida strains in a mouse model.
- To evaluate the role of mouse macrophages in controlling P. multocida infection.
- To assess the impact of opsonization on macrophage-mediated bacterial clearance.
Main Methods:
- Infection of ICR mice with P. multocida strains via different routes (intravenous, intraperitoneal, aerogenic).
- Assessment of bacterial multiplication in host organs (lungs, liver, spleen).
- In vitro assays using peritoneal and alveolar macrophages with opsonized and non-opsonized P. multocida.
Main Results:
- Turkey and calf P. multocida strains were highly virulent, causing rapid mortality.
- Rabbit P. multocida strain showed low virulence but increased with mouse passage.
- Opsonized P. multocida were rapidly inactivated by peritoneal macrophages.
- Alveolar macrophages showed slower inactivation of opsonized P. multocida, with subsequent bacterial multiplication.
- Hyperimmune mouse macrophages did not show enhanced inactivation of opsonized P. multocida.
Conclusions:
- Virulence of P. multocida strains varies significantly and can be influenced by host passage.
- Peritoneal macrophages play a key role in clearing opsonized P. multocida.
- Alveolar macrophages may be less effective, potentially contributing to persistent infection.
- Opsonization is critical for effective macrophage-mediated clearance of P. multocida.