Immunohistochemical detection of interleukin-12 and interferon-gamma in pigs experimentally infected with Mycoplasma hyopneumoniae

The expression of interleukin-12 (IL-12) and interferon-gamma (IFN-gamma) was examined immunohistochemically in the lungs of pigs aged 21 days infected experimentally with Mycoplasma hyopneumoniae (Mh). Ten pigs were inoculated intranasally with Mh and killed in pairs weekly from 7 to 35 days post-infection (dpi). Immunolabelling for IL-12 and IFN-gamma was usually associated with inflammation, particularly in macrophages and lymphocytes in the thickened alveolar septa and in the hyperplastic bronchus-associated lymphoid tissue (BALT). Cells positive for both cytokines were detected at 7 dpi, their numbers increasing at 14 and 21 dpi, and slightly decreasing thereafter. The results suggest that IL-12 and IFN-gamma play a role in pulmonary defence mechanisms against Mh infection.