Recombinant human granulocyte-macrophage colony-stimulating factor induces granule exocytosis from human polymorphonuclear neutrophils.

Exposure of human polymorphonuclear neutrophils (PMNs) to recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) resulted in a time- and concentration-dependent (3-100 units/ml) extracellular release of a specific (vitamin B12-binding protein) but not azurophil granule constituent (myeloperoxidase). Negligible granule exocytosis occurred if PMNs were not preincubated with cytochalasin B prior to contact with GM-CSF. The extent of degranulation elicited with GM-CSF was reduced but not abolished when PMNs were incubated with EGTA in calcium-free medium. GM-CSF did not stimulate a rise in the cytosolic-free calcium concentration ([Ca2+]i), and it had no effect on PMN protein kinase C (PKC) activity.