Immunolocalisation of P. multocida B:2 in the respiratory tracts of carriers. A. Serous glands in the nasal passage (bar = 100 μm). B. Tonsillar crypts mixed with cellular debris (bar = 100 μm). C. Ciliated tracheal epithelium (bar = 50 μm). D. Intracytoplasmic immunoreactivity in alveolar macrophages and on the surface of the alveolar sac (bar = 50 μm).