Arylsulfatase B is present in crystalloid-containing granules of human eosinophil granulocytes

Eosinophil granulocytes are characterized by large crystalloid-containing granules whose major contents of highly cationic proteins may play a role in allergic reactions and parasitic infections. Human eosinophils are also rich in arylsulfatase B whose enzymatic activity is localized to a population of small type cytoplasmic granules and used as a marker for such organelles. We utilized immunoelectron microscopy to investigate its subcellular distribution in human eosinophils. The arylsulfatase B antigen was found to be concentrated to both the crystalloid core and the matrix of crystalloid-containing granules as well as in small type granules. Therefore arylsulfatase seems to be present primarily in crystalloid-containing granules in a possibly inactive form (but detected by antibodies) that is converted to an enzymatically active form, e.g. during secretion and formation of small type granules which may derive from the former granules.