Pulmonary alveolar pores and alveolar macrophage-mediated particle clearance.

Pulmonary alveolar macrophages (AM) are considered to have an essential role in alveolar clearance of particles. The AM occupy only a small portion of the alveolar surface and their number is probably lower than the number of alveoli. Even at realistic experimental exposures the number of deposited particles, which are distributed all over the lung surface, is orders of magnitude higher than the number of AM. Phagocytosis of deposited particles, however, is being accomplished rapidly within hours. Based on microscopic evidence, we suggest that alveolar pores serve as important passageways for AM by shortening the distance between particles and AM. Accordingly, the pores of Kohn may, in part, lend efficiency to the in vivo particle collection by AM.