Immunohistochemical Labelling of Cytokines in Calves Infected Experimentally with Mycoplasma bovis

Summary 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.