Interferon-γ Enhances Superoxide Production by HL-60 Cells Stimulated with Multiple Agonists

Abstract

The production of superoxide anion (O⁻ ₂ ) by phagocytic cells plays an important role in host defenses and inflammatory processes. Interferon-γ (IFN-γ) primes neutrophils for increased O⁻ ₂ release stimulated by various agonists. This study examines if myeloid differentiated HL-60 cells also serve as a model for IFN-γ-induced priming, and examines mechanism by which this priming occurs. IFN-γ 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 O⁻ ₂ production was seen with IFN-γ at 0.1 U/ml, with optimal priming at 100 U/ml. The time course of priming by 100 U/ml IFN-γ 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-γ was completely inhibitied by 1 μg/ml cycloheximide. HL-60 cells cultivated with 100 U/ml IFN-γ produced increased O⁻ ₂ 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-γ 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-γ primes HL-60 cells, in part, by stimulating synthesis of proteins that participate in NADPH oxidase activation distal to the FMLP receptor.