Properties of concanavalin A-elicited granule exocytosis from human polymorphonuclear neutrophils

Abstract

Exposure of human neutrophils to concanavalin A (Con A) resulted in a time- and concentration-dependent extracellular release of granule-associated lysozyme but not beta-glucuronidase or cytosolic lactate dehydrogenase. Maximum extrusion of lysozyme occurred 30 min after cell contact with Con A. The percent of total granule enzyme activity discharged is insignificant when cells are not preincubated with cytochalasin B prior to being exposed to Con A (5-50 micrograms/ml). Granule enzyme release from Con A-treated cells is markedly inhibited by alpha-methyl-D-mannoside. Con A-elicited extrusion of lysozyme is reduced significantly, but not abolished, in the absence of extracellular calcium. However, contact between neutrophils and EGTA in calcium-free medium had no effect on Con A-stimulated release of granule enzymes. 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), an antagonist of intracellular calcium, caused a dose-dependent inhibition of lysozyme discharge from Con A-treated neutrophils. The activity of TMB-8 could be abrogated with the addition of calcium, but not magnesium, to the extracellular medium. Therefore, Con A and TMB-8 should serve as useful tools for elucidating the mechanism of granule enzyme release from neutrophils.