Reaction of macrophages to cigarette smoke. II. Immigration of macrophages to the lungs.

The present study identifies the source of the elevated pulmonary macrophage population in young adult male mice which results when animals are exposed to cigarette smoke. Light microscopic and autoradiographic analysis of pulmonary tissue from smoke-exposed animals revealed that pulmonary macrophages (free, attached, and septal or interstitial) divide only rarely. Further, it was noted that, during the marked progressive increase in the labeled macrophage population in the lungs, the number of silver grains over the nuclei of labeled macrophages did not become significantly diluted. Thus, the markedly elevated macrophage population which results when animals are exposed to cigarette smoke appears, for the most part, to be due to immigration of cells from bone marrow rather than in situ division of resident macrophages.