In vivo and in vitro studies of the cellular defense system of the human lung.

Magnetic microparticles were used to investigate the defence system of the human lungs against foreign material. About 0.5 mg of spherical monodisperse magnetite particles were deposited in the alveolar region of the human lung by voluntary inhalation. After primary magnetization a remanent magnetic field (RMF) of the lung can be measured that allows estimation of the amount of dust retained in the lung. The decay of this RMF, called relaxation, results from a misalignment of the dipole particles due to the activity of pulmonary macrophages. This macrophage activity was characterized by a cell energy Ez. With a secondary magnetization the lung can be remagnetized by rotation of the dipole particles. This allows estimation of the intracellular viscosity and the motility of the alveolar macrophages in vivo. The macrophage cell-line J774 was used to verify the dynamic processes of the magnetic particles within the cells in vitro. In vitro and in vivo relaxation curves of polydisperse and of spherical monodisperse magnetite particles are presented. Thermal relaxation of mono-disperse and polydisperse particles within a viscous standard could be verified with the Brownian rotary diffusion model. Relaxation with monodisperse particles was double exponential in vivo as well as in vitro, suggesting that 2 different viscous compartments of the cytoplasm should be considered. Relaxation in the macrophage cell-line J774 was particle-size-dependent.