Response of pulmonary macrophages to unilateral instillation of carbon

Production and delivery of macrophages to the alveoli are dependent upon chemotactic and mitogenic stimuli. To determine whether these mechanisms occur uniformly throughout the lungs or are localized to the areas of particulate deposition, the authors instilled 4 mg of carbon in one lung of a rat, the other lung serving as a control. Following split-lung lavage, little change was seen in the number of cells lavaged from nontreated lungs, whereas the yield of macrophages from the black lungs rose from 32 X 10(4) to 400 X 10(4) after 2 days; control values were not attained until 3 weeks. Labeling indices for cell nuclei in the white lungs were slightly elevated, whereas in the black lungs the value rose from 0.4 to 1.0-1.5% for 3 weeks before falling to normal. The increased labeling was limited to interstitial cells. The results provide further support for the dual origin of alveolar macrophages and indicate the importance of local generation of chemotactic and mitogenic factors in stimulating the cellular response and in directing these cells to the sites of maximal deposition of particles.