Role of myeloperoxidase in the luminol-dependent chemiluminescence response of phagocytosing human monocytes.

The luminol-dependent chemiluminescence (CL)-response of phagocytosing declined steadily during in vitro differentiation and was approximately 10% of the initial value by the fourth day of culture. A parallel decline in myeloperoxidase (MPO)-activity of monocyte cell lysates was observed during the same period, and a close correlation was found between peak luminol-dependent CL-response and MPO-activity. The lucigenin-dependent CL-response of phagocytosing monocytes in parallel cultures declined to about 85% of the initial value during four days of in vitro culture. Chemiluminescence was determined in solutions of luminol or lucigenin subjected to fixed amounts of H2O2 or enzymatically generated fluxes of H2O2. Horseradish peroxidase (HRPO) markedly enhanced the luminol-dependent CL but not the lucigenin-dependent CL of this cell-free system. Similar results were obtained when a crude MPO extract was substituted for the HRPO. Despite this evidence that luminol-dependent CL is enhanced by peroxidases, addition of HRPO to the assay medium did not increase the luminol-dependent CL-response of four days old, phagocytosing monocytes.