The Role of Macrophages in Particle Translocation from Lungs to Lymph Nodes

Red fluorescent and green fluorescent microspheres were instilled into separate but adjacent areas of dog lung lobes. After 7 days, the tracheobronchial lymph nodes that drained both of the instilled areas contained many macrophages with all red or all green microspheres but rarely both. This indicates that the particles did not translocate passively and that lung macrophages phagocytized the microspheres in the lung and carried them to the tracheobronchial lymph nodes. In addition, two populations of pulmonary alveolar macrophages (PAM's), one that had phagocytized red microspheres in vivo and one that had phagocytized green microspheres, were lavaged from the lungs of dogs, mixed into one population, and instilled back into a previously unexposed lung lobe of the same dogs. As in the first experiment, the tracheobronchial lymph nodes that drained the instilled area contained numerous macrophages with either all red or all green microspheres. This suggested that the instilled PAM's had migrated to the tracheobronchial lymph nodes. Thus, lung macrophages, including PAM's probably play a critical role in the induction of lung immunity and in protection from disease by determining particle translocation.