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Turkey macrophage and heterophil bactericidal activity against Pasteurella multocida
B G Harmon1, J R Glisson, J C Nunnally
1Department of Veterinary Pathology, College of Veterinary Medicine, University of Georgia, Athens 30602.
Abstract:
Bactericidal activity of turkey macrophages and heterophils was demonstrated in an in vitro colorimetric bactericidal assay. Two vaccine strains and one field isolate of Pasteurella multocida A:3,4 and a single isolate each of Escherichia coli and Staphylococcus aureus were compared for susceptibility to the bactericidal activity of turkey macrophages and heterophils. Only P. multocida A:3,4-strain M-9 (the least virulent strain) was susceptible to macrophage bactericidal activity in the absence of specific immune serum, whereas all three P. multocida A:3,4 organisms were killed when opsonized with specific immune serum. E. coli was susceptible to the bactericidal activity of macrophages, and S. aureus was resistant. All bacteria tested were highly sensitive to the bactericidal activity of intact turkey heterophils, regardless of the opsonin treatment. Electron microscopic findings suggested that heterophils may kill extracellular P. multocida. Only S. aureus and E. coli were killed by lysed heterophils.
Insights
Turkey macrophages and heterophils exhibit bactericidal activity against various bacteria. Heterophils effectively kill Pasteurella multocida, Escherichia coli, and Staphylococcus aureus, while macrophages show selective activity, especially with immune serum.
Area of Science:
- Veterinary Immunology
- Microbiology
- Cellular Biology
Background:
- Avian innate immune cells, specifically macrophages and heterophils, play a crucial role in combating bacterial infections.
- Understanding the differential bactericidal capabilities of these cells is vital for poultry health and disease management.
Purpose of the Study:
- To evaluate the in vitro bactericidal activity of turkey macrophages and heterophils against key bacterial pathogens.
- To compare the susceptibility of Pasteurella multocida, Escherichia coli, and Staphylococcus aureus to these innate immune cells.
Main Methods:
- In vitro colorimetric bactericidal assay utilizing turkey macrophages and heterophils.
- Testing susceptibility of bacterial isolates (Pasteurella multocida strains, Escherichia coli, Staphylococcus aureus) to cell-mediated killing.
- Assessment of bactericidal activity with and without specific immune serum (opsonization).
- Electron microscopy to investigate potential mechanisms of bacterial killing.
Main Results:
- Turkey heterophils demonstrated potent bactericidal activity against all tested bacteria (P. multocida, E. coli, S. aureus), irrespective of opsonization.
- Macrophage bactericidal activity was strain-dependent for P. multocida; only the least virulent strain was susceptible without serum.
- Opsonization with specific immune serum significantly enhanced macrophage killing of P. multocida.
- Escherichia coli was susceptible to macrophage killing, while Staphylococcus aureus was resistant.
- Electron microscopy suggested extracellular killing of P. multocida by heterophils.
Conclusions:
- Turkey heterophils are a primary defense against a broad spectrum of bacterial pathogens, potentially through extracellular mechanisms.
- Macrophage bactericidal efficacy against P. multocida is significantly enhanced by specific antibodies, highlighting the role of adaptive immunity.
- Differential susceptibility of bacteria to turkey macrophages and heterophils provides insights into host-pathogen interactions and immune evasion strategies.
