Infectious bronchopneumonia is a widespread disease in modern commercial pig production and Pasteurella multocida is frequently associated with the lesions. To evaluate porcine lung lesions associated with P. multocida, populations of inflammatory cells were examined by immunohistochemistry in necrotic lung lesions from nine pigs and exudative lung lesions from eleven pigs. Lungs from five pigs served as controls. All cases were selected from naturally infected pigs using co-infection based criteria to make them as comparable as possible. The inflammatory cells demonstrated by immunohistochemistry were T-lymphocytes (CD3 +, CD4 + and CD8 + subsets), B-lymphocytes, neutrophils, macrophages, and IgA +, IgM + and IgG + cells.
The results showed that (1) a significant increase in all inflammatory cells was found in lesions associated with P. multocida, (2) necrotic lesions had a larger number of CD3 + T-lymphocytes and IgA + cells, and (3) cases with exudative lesions had a more CD8 + T-lymphocytes, B-lymphocytes, macrophages and neutrophils. No differences in the numbers of CD4 + T-lymphocytes, IgG + and IgM + positive cells were found between necrotic and exudative cases. The results show that P. multocida significantly alters the inflammatory response in the lung and that lesions associated with P. multocida display diverse inflammatory responses according to their distinct morphological pattern.