Temporal adaptation of human neutrophil metabolic responsiveness to the peptide formylmethionyl‐leucyl phenylalanine: A comparison between human neutrophils and granule‐depleted neutrophil cytoplasts

When polymorphonuclear leukocytes (neutrophils) and soluble or particulate matter interact, the cells produce superoxide anions (O2−) and hydrogen peroxide (H2O2). The chemotactic peptide formylmethionyl-leucylphenylalanine (FMLP) induced a very weak response in normal neutrophils. The cellular response was changed, however, as a result of in vitro aging of the cells, i.e. the magnitude of the response was increased following storage of the cells at 22°C for up to 120 min, in the absence of any stimulus, and before the addition of the peptide. When phorbol myristate acetate was used as a stimulus, there was a pronounced production of O2− and H2O2, but no change in magnitude as a result of in vitro aging. When neutrophil cytoplasts (granule-free vesicles of cytoplasm enclosed by plasmalemma) were exposed to the peptide FMLP of PMA, the vesicles produced both O2− and H2O2. There was, however, no increase in oxidative metabolite production in cytoplasts as a result of in vitro aging when either FMLP or PMA was used as a stimulus. The results thus indidate that mere incubation at room temperature primed the cells to increase their production of oxidative metabolites as a result of spontaneous exposure of hidden receptors. The fact that no such effects were observed with cytoplasts indicates that spontaneous receptor recruitment is a granule-dependent process.