CELL-SIZE OF ALVEOLAR MACROPHAGES - AN INTERSPECIES COMPARISON

Alveolar macrophages (AM) play a critical role in the removal of inhal ed particles or fibers from the lung. Species differences in AM size m ay affect the number and size range of particles/fibers that can be ac tually phagocytized and cleared by AM. The purpose of this study was t o compare the cell size of rat, hamster, monkey, and human AM by selec tive flow cytometric analysis of cell volume. Resident AM from CD rats , Syrian golden hamsters, cynomolgus monkeys, and nonsmoking, healthy human volunteers were harvested by standard bronchoalveolar lavage pro cedures. Morphometric analysis of AM was performed using a flow cytome ter that generates volume signals based on the Coulter-type measuremen t of electrical resistance. We found that hamster and rat AM had diame ters of 13.6 +/- 0.4 mu m (n = 8) and 13.1 +/- 0.2 mu m (n = 12), resp ectively. Comparatively, the AM from monkeys (15.3 +/- 0.5 mu m, n = 7 ) and human volunteers (21.2 +/- 0.3 mu m, n = 10) were larger than th ose from rats and hamsters. The AM from humans were significantly larg er (p < 0.05) than those from all other species studied, corresponding to a 4-fold larger cell volume of human AM (4990 +/- 174 mu m(3)) com pared to hamster (1328 +/- 123 mu m(3)) and rat (1166 +/- 42 mu m(3)) AM. In summary, we have found marked species differences in the cell s ize of AM. We suggest that the number and size range of particles/fibe rs that can be phagocytized and cleared by AM may differ among species due to inherent or acquired species differences in AM cell size.