Association of ⁵⁹Iron Oxide with Alveolar Macrophages during Alveolar Clearance

Abstract

Long-Evans hooded rats were exposed for 2 b to aerosols of hydrated, radio-labeled iron (⁵⁹Fe) oxide (MMAD = 1.6 μm; s`g = 3.0) in order to produce a low mass burden of particles (≅ 30 μg) 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 b, > 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 × 10⁷ 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 × 20⁵ cells.