Schematic representation of eosinophil granule maturation with proposed staining patterns. ProMBP is deposited into large vacuoles just proximal to the Golgi. From here, proMBP containing vacuoles appear to move toward the periphery where granule condensation begins to occur. As the granule condenses, proMBP can be seen around the periphery, and MBP can be seen in the interior. During the final stage of granule maturation, proMBP reactivity is lost, and only MBP reactivity remains.