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Study of bovine pulmonary response to Pasteurella haemolytica: pulmonary macrophage response
Abstract:
A resistance state was produced in the bovine lung by exposing calves to an aerosolized mist of Pasteurella haemolytica. Verification of the resistant state was determined by an increase in clearance of P haemolytica from lungs of exposed calves vs lungs from nonexposed calves over 24 hours. Bovine pulmonary macrophages isolated from lung washings of calves exposed to P haemolytica and from lungs of nonexposed calves failed to phagocytize P haemolytica in vitro. Whole serum, pulmonary immunoglobulin (Ig) A, and IgG from exposed and nonexposed calves did not enhance phagocytosis as measured by 14C uptake or fluorescent antibody staining.
Insights
Calves exposed to Pasteurella haemolytica developed a resistant lung state, showing increased bacterial clearance. However, their pulmonary macrophages and immune factors failed to enhance bacterial phagocytosis in vitro.
Area of Science:
- Veterinary Immunology
- Bovine Respiratory Disease
- Bacteriology
Background:
- Bovine respiratory disease is a significant economic concern in cattle farming.
- Pasteurella haemolytica is a primary pathogen implicated in bovine pneumonia.
- Understanding host resistance mechanisms is crucial for disease prevention.
Purpose of the Study:
- To investigate the development of a resistant lung state in calves following exposure to Pasteurella haemolytica.
- To evaluate the phagocytic capacity of bovine pulmonary macrophages and the role of serum immunoglobulins in this resistant state.
Main Methods:
- Calves were exposed to aerosolized Pasteurella haemolytica to induce a resistance state.
- Bacterial clearance from lungs was measured over 24 hours in exposed and nonexposed calves.
- Bovine pulmonary macrophages were isolated and their in vitro phagocytosis of P. haemolytica was assessed.
- The effect of whole serum, IgA, and IgG on phagocytosis was evaluated using 14C uptake and fluorescent antibody staining.
Main Results:
- Exposure to Pasteurella haemolytica successfully induced a resistant lung state in calves.
- A significant increase in the clearance of P. haemolytica was observed in exposed calves compared to controls.
- Bovine pulmonary macrophages from exposed calves did not exhibit enhanced phagocytosis of P. haemolytica in vitro.
- Neither whole serum nor specific immunoglobulins (IgA, IgG) from exposed or nonexposed calves improved phagocytosis.
Conclusions:
- Calves can develop a lung resistance state against Pasteurella haemolytica, characterized by enhanced bacterial clearance.
- This resistance is not mediated by improved macrophage phagocytosis or opsonization by serum IgA or IgG in vitro.
- Further research is needed to elucidate the mechanisms underlying this non-phagocytic resistance.