THE IMMUNE-SYSTEM OF THE RESPIRATORY-TRACT IN PIGS

Although the lung is not a lymphoid organ it contains large numbers of lymphocytes. These can be found in different compartments: (1) the pu lmonary intravascular pool, which is organ-specific and shows a unique migration pattern; (2) the interstitial lymphocyte pool, which is equ ivalent in size to the whole blood pool; (3) the bronchus-associated l ymphoid tissue (BALT) which develops as a result of microbial stimulat ion; (4) the intraepithelial and lamina propria lymphocytes of the bro nchi, with their typical subset composition; (5) the lymphocytes in th e bronchoalveolar space, which can be sampled by bronchoalveolar lavag e. The size and kinetics of the lymphocyte pools have been studied in the pig in more detail than in most other species. Despite this organo typic compartmentalisation of the pulmonary lymphoid cells in the pig, the lung is part of the integrated mucosal immune system, as shown by protective oral immunisation against the lung-pathogenic bacteria Act inobacillus pleuropneumoniae. The lung immune system in the pig is not only of veterinary interest, but also a relevant model for the human respiratory tract.