Three-Dimensional Consecutive Observation for the Reaction of Brain Immune cells, microglia, Using Scanning Acoustic Microscopy

This study proposes that scanning acoustic microscopy (SAM) distinguishes living cells’ three-dimensional and dynamic structural changes during physiological reactions. Using SAM, we observed physiological immune cell function. Microglia (MG) is a type of immune cell in the brain, and they migrate and contact damaged cells to scavenge them, a process known as phagocytosis. However, the three-dimensional and dynamic interaction between MG and damaged cells is unknown. Using a novel SAM approach, we investigated MG’s morphological changes to scavenge damaged neurons. The results showed that MG engulfed damaged granule cells (GC) during phagocytosis. The acoustic impedance of the same MG differed depending on whether they were in contact with GC, and the contact resulted in higher acoustic impedance areas. In addition, optical observations showed cytoskeletal actin polymerization in regions of high acoustic impedance. These results indicate that MG engulfs and phagocytose GC by polymerizing actin and increasing the stiffness around the GC. We suggest that the cytoskeleton is a potential target for controlling phagocytosis, and the SAM is an effective tool for observing three-dimensional cell-cell interactions during phagocytosis and the associated changes in mechanical properties.