Origin and Kinetics of Pulmonary Macrophages during an Inflammatory Reaction Induced by Intra-alveolar Administration of Aerosolized Heat-killed BCG1

This report describes the kinetics of the total population of pulmonary macrophages and their immediate precursors during a slight acute inflammation induced by an aerosol of heat-killed BCG in specific pathogen-free mice. The total number of pulmonary macrophages isolated by lavage and subsequent enzyme digestion of lung tissue rose to 150% of normal in the first 4 h and then diminished gradually, reaching normal levels at 144 h after exposure. The number of monocytes showed a transient rise to 130% of the normal value in the first 24 h after exposure. Analysis of data from 3H-thymidine labeling experiments showed that the increase in pulmonary macrophages was due to the influx of 1.7 × 106 circulating monocytes within 24 h after exposure. In the first 4 h after the aerosol, the monocyte influx rate was 25 times higher than in the normal steady state and then decreased. The frequency of locally dividing pulmonary macrophages, reflected by in vitro labeling, did not differ from that found in animals in th...