Production of IL-8 and Release of Eosinophil-Derived Neurotoxin by Normal Peripheral Blood Eosinophils

To study the regulation of IL-8 production and release of eosinophil-derived neurotoxin (EDN) by normal blood eosinophils, we isolated eosinophils from healthy individuals and stimulated them with immobilized secretory IgA with or without exogenous IL-5 for 3, 12, and 24 h, and with different concentrations of ionomycin for 24 h. Eosinophils cultured with secretory IgA for 3 and 12 h showed strong expression of mRNA for IL-8 by reverse transcription polymerase chain reaction. Exogenous IL-5 enhanced mRNA for IL-8 expression by eosinophils after 24 h of incubation. IL-8 secretion increased in a time-dependent manner throughout the 24 h of observation; in contrast, EDN release reached a plateau value after 12 h. Furthermore, at least 2 µM ionomycin was necessary for induction of IL-8 secretion, whereas 0.5 µM induced detectable EDN release by eosinophils. These results suggest that the mechanism of eosinophil degranulation may be different from those of cytokine secretion.