Migration of neutrophils from lung to tracheobronchial lymph node

Translocation of particulate antigen deposited in the lung to tracheobronchial lymph nodes (TBLN) is important in the induction of pulmonary immune responses. We have previously shown that alveolar macrophages can contribute to particle translocation to TBLN, but whether neutrophils can also contribute to this process is not known. To determine if neutrophils can carry particles to the TBLN, dog neutrophils were elicited by instillation of red or green fluorescent microspheres into individual lung lobes. Autologous neutrophils that had phagocytized fluorescent microspheres were then instilled into an unexposed lobe of the same dog's lung. After 24 hr, the TBLN of instilled dogs had numerous neutrophils, 99% of which contained either red or green fluorescent microspheres but not both. Use of the two different colored microspheres as labels precluded the possibility that neutrophils had phagocytized the microspheres in the TBLN. In a second experiment, dogs were depleted of peripheral blood neutrophils by injections of hydroxyurea. Hydroxyurea-treated and normal dogs were instilled with fluorescent microspheres and killed after 40 h. Hydroxyurea treatment reduced neutrophil accumulation in the lung by 79% and reduced particle translocation to the TBLN by 80%. Results of these experiments indicate that neutrophils are similar to pulmonary alveolar macrophages (PAM) in their ability to phagocytize particles in the lung and then migrate to the TBLN.