Tilmicosin does not inhibit interleukin-8 gene expression in the bovine lung experimentally infected with Mannheimia (Pasteurella) haemolytica

The expression of the interleukin-8 (IL-8) gene was examined by in situ hyb ridization in lung tissues from calves experimentally infected with Mannhei mia (Pasteurella) haemolytica and treated with tilmicosin. Interleukin-8 mR NA expression was detected in alveolar areas, particularly along interlobul ar septa, in the lumen, and in the epithelial cells of some bronchioles. In lesional lung tissues from animals that had received tilmicosin, we found large areas with limited inflammation. There was no staining for IL-8 mRNA in these areas. In contrast, in strongly inflamed areas, the same patterns and intensities of staining for IL-8 mRNA were detected in tilmicosin- and sham-treated animals. We conclude that tilmicosin does not affect the expre ssion of IL-8 mRNA in tissue showing microscopic signs of inflammation. Tog ether with previous reports, this supports the view that the pro-apoptotic properties of tilmicosin on neutrophils do not compromise the host defense mechanisms required to control the infection.