The respiratory immune system of pigs

Respiratory tract infections with bacteria like Actinobacillus pleuropneumoniae are extremely common in pigs and are of major veterinary relevance. The respiratory tract can be divided into the upper part, consisting of the nose, pharynx, larynx and trachea, and the lower part, consisting of the different parts of the lung. After bronchoscopy and bronchoalveolar lavage (BAL) had been established for pigs, interest grew in the unspecific parts of the immune system of the respiratory tract (such as macrophages, mast cells, the mucociliary function) and the specific immune system, consisting of the different lymphocyte subsets. In contrast to the rodent and human lung, the lung of the pig contains large numbers of intravascular macrophages with a high clearance capacity. The main focus of this paper is the localization, subset composition and quantification of lymphocytes in the pig lung: the intravascular and interstitial pool and the lymphocytes in the bronchial epithelium and lamina propria including bronchus-associated lymphoid tissue form the major compartments. In the BAL only a small proportion of nucleated cells are lymphocytes. The effects of age, antigen exposition, immunization and infection on the lymphocyte distribution in the pig lung are presented. In addition to veterinary aspects, the lung of pigs can also serve as a model for diseases in humans.