Interferon-gamma enhances superoxide production by HL-60 cells stimulated with multiple agonists

The production of superoxide anion (O2-) by phagocytic cells plays an important role in host defenses and inflammatory processes. Interferon-gamma (IFN-gamma) primes neutrophils for increased O2- release stimulated by various agonists. This study examines if myeloid differentiated HL-60 cells also serve as a model for IFN-gamma-induced priming, and examines mechanism by which this priming occurs. IFN-gamma enhanced HL-60 cell superoxide production in response to F-Met-Leu-Phe (FMLP) in a concentration-dependent manner. Following a 4-h exposure, an increase in O2- production was seen with IFN-gamma at 0.1 U/ml, with optimal priming at 100 U/ml. The time course of priming by 100 U/ml IFN-gamma showed that at least a 1-h exposure was required, and a maximal effect was seen at 24 h. Priming after a 4-h exposure to 100 U/ml IFN-gamma was completely inhibited by 1 micrograms/ml cycloheximide. HL-60 cells cultivated with 100 U/ml IFN-gamma produced increased O2- when exposed to 25 mM NaF (containing AIF4) or 10 nM phorbol myristate acetate, agonists that trigger the respiratory burst independent of receptor stimulation. These results indicate that IFN-gamma primes the HL-60 cell respiratory burst in a concentration and time-dependent manner similar to its effect on neutrophils. The data are consistent with the hypothesis that IFN-gamma primes HL-60 cells, in part, by stimulating synthesis of proteins that participate in NADPH oxidase activation distal to the FMLP receptor.