UFP are endocytosed by alveolar macrophages. Electron microscopy photographs of a lipid-laden alveolar macrophage harvested from an apoE-/- mouse exposed to concentrated ambient ultrafine particles (<0.18 μm). Red arrows indicate electron-dense material corresponding to intracellular aggregates of nanoparticles. Notice the subcellular mitochondrial localization encircled by the red dotting. Source: Journal cover of Araujo et al .