RESPIRATORY-TRACT DEFENSE-MECHANISMS IN PIGS

In pigs, as in all terrestrial vertebrates, the zone of respiratory exchange is an internalized structure, protected from atmospheric hazards by the respiratory airways. This ductal system is responsible for trapping and destroying pathogens, for humidifying and heating inhaled air, and for disposal of particulate material deposited on the respiratory membrane. Porcine lung is characterized by the absence of openings between adjacent respiratory units and, therefore, the absence of collateral ventilation. The high frequency and the limited spread of pneumonias in pigs relate to these characteristics. Major non-specific defense mechanisms responsible for the continuous cleaning of the lungs and the respiratory airways are the muco-ciliary apparatus and the alveolar macrophage. Other mechanisms, specifically activated in presence of one particular pathogen, are the immunoglobulins of the respiratory mucosa (IgA and IgG) and the cells responsible for cell-mediated immunity.