Hypereosinophilic syndrome human eosinophil degranulation induced by soluble and particulate stimuli

Eosinophil degranulation induced by the calcium ionophore A23187 and opsonized zymosan particles was examined ultrastructurally in peripheral blood cells obtained from patients with the hypereosinophilic syndrome. Unstimulated hypereosinophilic syndrome eosinophils contained altered, vacuolated cytoplasmic granules and large cytoplasmic crystalloid structures not seen in normal cells. By morphometric analysis of transmission electron micrographs, the hypereosinophilic syndrome eosinophils contained a larger percentage of smaller sized cytoplasmic granules than normal cells. The hypereosinophilic syndrome eosinophils, however, were capable of undergoing noncytotoxic degranulation after stimulation with either A23187 or opsonized zymosan. Hypereosinophilic syndrome eosinophil degranulation was characterized by fusion of the perigranular membranes of adjacent cytoplasmic granules and vesiculation of the fused granules. Granule contents were released intracellularly into vacuoles after ionophore stimulation and into phagosomes containing the ingested zymosan particles. Noncytotoxic extracellular release of eosinophil peroxidase (EPO) was also observed after cell stimulation by either A23187 or zymosan. The capacity of hypereosinophilic syndrome eosinophils to degranulate after appropriate stimulation with release of toxic granule constituents such as EPO and other basic proteins may be important in the tissue injury observed in this syndrome.