Stimulation of Human Neutrophils by Soluble and Insoluble Immunoglobulin Aggregates. Secretion of Granule Constituents and Increased Oxidation of Glucose

Reaction of human neutrophils with aggregated immunoglobulin on nonphagocytosable surfaces results in secretion of granule enzymes (exocytosis of granules) and stimulation of glucose oxidation by the nexose monophosphate pathway (HMP). The role of HMP stimulation in the enzyme secretion and some requirements for the two neutrophil activities have been examined. It was found that (a) HMP stimulation could be selectively inhibited under conditions where release of granule enzymes remained unchanged or was enhanced, for example, by reduced glucose concentration or by 2-deoxyglucose. (b) Removal of Ca++ and addition of agents which increased the intracellular levels of cyclic AMP (cAMP), however, prevented both activities, while colchicine had greater inhibitory activity on HMP stimulation than upon secretion. (c) Neutrophils incubated in suspension with particulate aggregated gamma-globulin phagocytosed the particles and exhibited a stimulated HMP and released granule enzymes. In contrast, incubation in suspension with soluble aggregated gamma-globulin resulted in the stimulated HMP only. Granule evzymes were not liberated. 300-fold less soluble aggregates bound to a surface, however readily induced exocytosis of granules from adherent neutrophils. This demonstrates the importance of surface effects in the induction of secretion from neutrophils. Aggregated immunoglobulin reacting with neutrophil Fc receptors thus induces both degranulation (exocytosis) and increased HMP activity. The pathways leading to these events are separable although apparently sharing some common steps, including the initiating events.