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Inactivation of Pasteurella multocida within the mouse peritoneal cavity
Abstract:
Normal ICR mice were injected intraperitoneally with 0.5 ml of thioglycollate broth or 5 x 10(8) heat-killed Pasteurella multocida vaccine and the number of polymorphs, lymphocytes and macrophages in the peritoneal washout suspensions were determined at intervals up to 72 hours. The stimulated mice were challenged intraperitoneally with opsonized or unopsonized P. multocida at increasing time intervals and the rate of growth by the organisms in the washout suspension was determined up to 60 minutes later. The opsonized bacilli were taken up by the 6 hr. exudate cells (50-60% PMNs) and their growth inhibited more effectively than when the 72 hr exudate cells were tested (only 10% PMNs). When the challenge inoculum was introduced into the peritoneal cavities of mice stimulated 6 hrs previously with 5 x 10(8) heat-killed P. multocida vaccine, up to 80% of the bacilli were inactivated over a 30 minute period. However, when 72 or 250 hr peritoneal exudate cells were tested, the inoculum was not inactivated, but showed an increasingly lethal effect.
Insights
Early immune cell responses in mice, specifically polymorphonuclear neutrophils (PMNs), effectively combat Pasteurella multocida. Later responses with fewer PMNs are less effective, highlighting the importance of early cellular immunity.
Area of Science:
- Immunology
- Microbiology
Background:
- The innate immune system's response to bacterial challenge is crucial for host defense.
- Peritoneal exudate cells play a significant role in clearing bacterial infections.
Purpose of the Study:
- To investigate the kinetics of peritoneal immune cell populations following stimulation.
- To evaluate the efficacy of these immune cells in clearing Pasteurella multocida at different time points.
Main Methods:
- ICR mice were injected with thioglycollate broth or heat-killed Pasteurella multocida vaccine.
- Peritoneal washout suspensions were analyzed for polymorphs, lymphocytes, and macrophages up to 72 hours.
- Stimulated mice were challenged with P. multocida, and bacterial growth in peritoneal washout was assessed.
Main Results:
- Six-hour exudate cells, rich in polymorphonuclear neutrophils (PMNs), effectively inhibited opsonized P. multocida growth.
- Seventy-two-hour exudate cells, with significantly fewer PMNs, showed reduced inhibition of bacterial growth.
- Early stimulation (6 hours) led to 80% inactivation of P. multocida within 30 minutes, while later stimulation (72-250 hours) resulted in increased lethality.
Conclusions:
- The composition of peritoneal exudate cells, particularly the proportion of PMNs, dictates the effectiveness against P. multocida.
- Early-acting innate immune cells are critical for controlling bacterial proliferation and preventing lethal infection.