Pathways of cellular efflux and particulate clearance after carbon instillation to the lung

The pulmonary response to the deposition of carbon particles was investigated to determine the routes of cellular efflux and the mechanisms of particulate clearance. At intervals to 6 months after the intratracheal instillation of 4 mg carbon, the lungs of mice were fixed in situ by perfusion without lavage. Within a few hours, migration of granulocytes into the bronchioles was observed; large numbers of PMNs were not seen in alveoli until 24 h. Associated with the PMN efflux there was transient oedema with no evidence of pulmonary cell necrosis. The number of free macrophages increased in response to the carbon and mononuclear cell migration into alveoli and bronchioles was also observed. The bronchiolar component of the cellular efflux indicates that PMNs and macrophages recovered from the lung by lavage are not entirely of alveolar origin. Whereas most particles, either free or in phagocytic cells, were cleared by the bronchial tree, some transepithelial passage of free particles to the interstitium was observed. Some carbon was found in hilar lymph nodes but overall lymphatic clearance was low.