Evidence for the Activation of Myeloperoxidase by f-Meth-Leu-Phe Prior to Its Release from Neutrophil Granulocytes

Abstract

Activity and release of myeloperoxidase (MPO) was measured in heparinized whole blood samples after activation of neutrophil granulocytes by the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP) using two different methods: (i) by determination of theamountof MPO released into the blood plasma using a MPO enzyme-immunoassay, and (ii) simultaneously, by measuring the remainingactivitywithin the neutrophils by flow cytometry using the Bayer Technicon H3. Although a part of MPO was released immedi ately after addition of fMLP, remaining MPO activity within the neutrophils surprisingly increased during the first minutes after incubation. Subsequently, MPO activity dropped due to a continuous release of MPO. In addition to fMLP, granulocyte-macrophage colony stimu lating factor (GM-CSF) enhanced MPO activity in neutrophils. These results indicate that MPO is present in resting granulocytes in an inactive or only partially active form and is activated by fMLP and GM-CSF.