Pathological and immunohistochemical studies of natural and experimental Mycoplasma bovis pneumonia in calves.

Lung tissues from calves naturally and experimentally infected with Mycoplasma bovis were subjected to histopathological and immunohistochemical examination. The latter was carried out with a monoclonal antibody raised against M. bovis, and an avidin-biotin-peroxidase complex (ABC) detection substrate system. Pulmonary lesions in naturally infected calves included exudative bronchopneumonia and extensive foci of coagulative necrosis surrounded by inflammatory cells. Experimentally infected lungs showed suppurative bronchiolitis and varying degrees of peribronchiolar mononuclear cell cuffing. M. bovis antigen in field cases was mainly detected at the periphery of the areas of coagulative necrosis, in necrotic exudates, and in close association with infiltrating macrophages and neutrophils. In lung tissue from calves with induced M. bovis pneumonia, antigen was located in epithelial cells, within inflammatory cells in airway lumina, and in alveolar walls. Other microbiological observations suggested that the ability of M. bovis to invade and cause lung parenchymal damage could be influenced by the participation of other pathogens.