Magnetometry of ingested particles in pulmonary macrophages.

Sensitive magnetometry has shown that, after inhalation of airborne magnetic dust by humans or animals, particles retained within the lungs rotate. A number of mechanisms for this rotation have been proposed, including motions of breathing, particle thermal energy, cardiac pulsations, surface fluid flows, and macrophage cytoplasmic movements. In this study the cellular mechanism was examined by magnetometry and videomicroscopy of pulmonary macrophages removed from hamster lungs 1 day after inhalation of a maghemite (gamma-Fe2O3) aerosol. The field remaining after magnetization was measured in adherent cells and was found to decay rapidly to 30 percent of its initial magnitude within 12 minutes. The remanent-field decay rate was slowed by inhibitors of cytoplasmic motion. Videomicroscopy of pulmonary macrophages with phagocytized gamma-Fe2O3 showed amoeboid motions that rotated the particles away from their original direction of magnetization. The results confirm that macrophage cytoplasmic movement is a primary cause of remanent-field decay in lungs and that magnetometry can be used to quantify intracellular contractile activity.