The mice were sacrificed at the indicated time points and their organs were removed for histological study. Sections of the right lobe of the liver were cut in the axial plane; splenic sections were also cut in the axial plane and included the hilum. Lung sections were cut in the coronal plane and included the hilum. Sections from the heart, great vessels, gastrointestinal tract, and kidney were cut in the coronal plane. Sections (4 µm in thickness) of paraffin-embedded organs were stained with Prussian blue to identify the accumulation of iron oxide. Macrophages were immuno histochemically stained with F4/80. Areas stained with Prussian blue and F4/80 were compared. For quantitative assessment, Prussian-blue-stained areas (µm 2 ) in a single field of view (magnification ×200) of three different lesions for each histological section were measured using Image-Pro ® Plus software (Media Cybernetics, Bethesda, MD) and average values were calculated.