Ultrastructure and cytochemistry of the cell surface of eosinophils

Eosinophils, isolated from the peritoneal exudate of rats through the use of metrizamide gradient were characterized by ultrastructural cytochemistry, scanning electron microscopy and freeze-fracture. The cell surface was analysed using the following cytochemical techniques combined with electron microscopy: (a) periodic acid-thiosemicarbazide-silver proteinate; (b) ruthenium red and (c) concanavalin A-horseradish peroxidase. The results indicate that the eosinophils have a glycocalyx which reacts strongly to all techniques used. With the use of these techniques it was also possible to distinguish invaginations of the cell membrane from cytoplasmic vesicles. By scanning electron microscopy it was possible to visualize the surface of the eosinophils during spreading on a glass surface. Cells rich in finger-like microvilli and flattened projections were identified. With the freeze-fracture technique we determined the density of the intramembranous particles on the P and E faces of the plasma membrane and the membrane of the specific granules.