Association of 59iron oxide with alveolar macrophages during alveolar clearance

Long-Evans hooded rats were exposed for 2 h to aerosols of hydrated, radiolabeled iron (59Fe) oxide (MMAD = 1.6 micron; sigma g = 3.0) in order to produce a low mass burden of particles (approximately equal to 30 micrograms) in the lung. The kinetics of particle clearance and the association of the particles with alveolar macrophages (AM) were measured. Two to four hours after exposure, lavaged particles were linearly related to AM numbers harvested, and 60% of the 59Fe activity was physically associated with AM. By 24 h, greater than 90% of the lavaged particles were associated with AM. Such an association was found for at least 75% of the particulate burdens in the lungs. If all the 59Fe is assumed to be AM associated, the 59Fe per AM predicts the total AM population size to be 2.14 X 10(7) cells. This number, in conjunction with the alveolar clearance rate of the particles, suggested the number of AM leaving the lung daily was 2.8 X 10(5) cells.