The Mechanisms which Produce Vacuolated and Degranulated Eosinophils

S ummary . As blood eosinophils in patients with an eosinophilia may contain refractile‘vacuoles’(vacuolated eosinophils), and some cells contain only a few granules (degranulated eosinophils) which show ultrastructural changes, experiments were done to see whether similar morphological alterations could be induced in blood eosinophils from normal people. Overnight culture of normal eosinophils with serum treated with cobra venom factor induced refractile‘vacuoles’and ultrastructural changes in granule matrix material. On the other hand, concanavalin A, 10 μ/ml for 2 h, led to the formation of larger perinuclear vacuoles containing granule contents, and ultrastructural changes were more marked in granule crystalloid material. Cytochalasin B inhibited these effects of concanavalin A. Neither of these stimuli caused a marked reduction in the number of cytoplasmic granules, but lysolecithin and insoluble (but not soluble) immune complexes produced large endocytic vacuoles into which partially solubilized and whole eosinophil granules were discharged. These results suggest that eosinophil granules can be affected in two distinct ways. In one, the granule matrix is altered leading to the light microscopy appearances of small refractile ‘vacuoles’. In the second, the crystalloid material is dispersed into the matrix. These apparently distinct steps precede the release of the granule contents into large cytoplasmic spaces or to the outside of the cell. Also, as patients' eosinophils may show one or both of these alterations it is suggested that they are distinct events. As concanavalin A induced solubilization of granules did not result in release to the outside, it is also proposed that an additional stimulus may be required to produce exocytosis of eosinophil granule contents. Further studies may show how these processes are linked, and their relative importance in eosinophil effector functions.