Two distinct mechanisms for stimulation of oxygen-radical production by polymorphonuclear leucocytes

Oxygen-radical production stimulated from rat polymorphonuclear leucocytes by either unopsonized latex particles (diameter = 1.01 microM) or chemotactic peptide (N-formyl-Met-Leu-Phe) was monitored by using luminol-dependent chemiluminescence. Azide inhibited by more than 80% the luminescence response induced by chemotactic peptide whether added before or after stimulation. However, the luminescence response to latex particles was progressively less susceptible to azide inhibition if the azide was added after the stimulus. Cytochalasin B, which was shown to abolish phagocytosis of the latex beads, also abolished the chemiluminescence response. However, the same cells showed a greatly enhanced response to chemotactic peptide. Cytochalasin B-treated cells secreted approx. 45% of total cellular myeloperoxidase in response to chemotactic peptide, but there was no detectable secretion in response to unopsonized latex particles. Microperoxidase equivalent to 20% of cellular peroxidase activity added to the cells before addition of the stimulus had no effect on the response to latex particles but increased approx. 2-fold the peak rate of chemiluminescence induced by chemotactic peptide. It was concluded that the unopsonized latex particles stimulated oxygen-radical production by the mechanism that involved endocytosis, whereas chemotactic peptide stimulated production by a mechanism that involved exocytosis of myeloperoxidase, the latter mechanism requiring an increase in intracellular free [Ca2+].