Immunohistochemical labelling of cytokines in calves infected experimentally with Mycoplasma bovis.

To gain further insight into the pathogenesis of Mycoplasma bovis-associated pneumonia, cytokine expression in different pulmonary compartments was examined. The expression of tumour necrosis factor (TNF)-α, interleukin (IL)-4 and interferon (IFN)-γ was examined immunohistochemically in the lung of 10 calves infected experimentally with M. bovis. M. bovis antigen was located in respiratory epithelial cells and within inflammatory cells in the airway lumina. Immunolabelling for TNF-α, IL-4 and IFN-γ was usually associated with inflammation, particularly in macrophages and lymphocytes in hyperplastic bronchus-associated lymphoid tissue (BALT), in thickened alveolar septa and in the bronchoalveolar exudate of infected animals. In M. bovis infection, macrophage and lymphocyte activation results in expression of a number of cytokines capable of inducing lung lesions and hyperplasia of the BALT. The cytokines examined likely play a role in pulmonary defence against M. bovis infection.