Myeloperoxidase Exocytosis from Activated Neutrophils in the Presence of Heparin

Exocytosis of myeloperoxidase (MPO) from activated neutrophils has been investigated in the presence of the anionic polysaccharide heparin. The optimal concentration of heparin (0.1 U/mL), which did not cause additional activation of cells (lack of augmentation of lysozyme exocytosis from specific and azurophilic granules), was determined. After preincubation of cells with heparin (0.1 U/mL) MPO exocytosis from neutrophils was stimulated by various activators (fMLP, PMA, plant lectins CABA and PHA-L) and was higher as compared to the effects of the activators alone. Experiments performed using MPO isolated from leukocytes have shown that heparin in the range of concentrations 0.1–50 U/mL had no effect on MPO peroxidase activity. Thus, the use of heparin at a concentration of 0.1 U/mL avoids the artifact caused by the “loss” of MPO due to its binding to neutrophils and increases the accuracy of the method of registration of degranulation of neutrophil azurophilic granules based on determination of the MPO concentration or its peroxidase activity in cell supernatants.