EVIDENCE FOR THE ACTIVATION OF MYELOPEROXIDASE BY F-METH-LEU-PHE PRIOR TO ITS RELEASE FROM NEUTROPHIL GRANULOCYTES

Activity and release of myeloperoxidase (MPO) was measured in heparini zed whole blood samples after activation of neutrophil granulocytes by the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP) us ing two different methods: (i) by determination of the amount of MPO r eleased into the blood plasma using a MPO enzyme-immunoassay, and (ii) simultaneously, by measuring the remaining activity within the neutro phils by how cytometry using the Bayer Technicon H3. Although a part o f MPO was released immediately after addition of fMLP, remaining MPO a ctivity 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-macrophag e colony stimulating factor (GM-CSF) enhanced MPO activity in neutroph ils. These results indicate that MPO is present in resting granulocyte s in an inactive or only partially active form and is activated by fML P and GM-CSF. (C) 1997 Academic Press.