Interleukin-8 primes oxidative burst in neutrophil-like HL-60 through changes in cytosolic calcium

In response to a variety of stimuli, neutrophils release large amount of reactive oxygen species (ROS) generated by NADPH oxidase. This process known as the respiratory burst is dependent on cytosolic free calcium concentration ([Ca2+]i). Proinflammatory cytokines such as interleukin-8 (IL-8) may modulate ROS generation through a priming phenomenon. The aim of this study was to determine the effect of human IL-8 on ROS production in neutrophil-like dimethylsulfoxide-differentiated HL-60 cells (≠HL-60 cells) and further to examine the role of Ca2+ mobilization during the priming. IL-8 at 10 nM induced no ROS production but a [Ca2+]i rise (254 ± 36 nM). IL-8 induced a strongly enhanced (2 fold) ROS release during stimulation with 1 μM of N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLF). This potentiation of ROS production is dependent of extracellular Ca2+ (17.0 ± 4.5 arbitrary units (A.U.) in the absence of Ca2+ versus 56.6 ± 3.9 A.U. in the presence of 1.25 mM of Ca2+). Also, IL-8 enhanced fMLF-stimulated increase in [Ca2+]i (375 ± 35 versus 245 ± 21 nM, 0.1 μM of fMLF). IL-8 had no effect on ≠HL-60 cells in response to 1 μM of thapsigargin (472 ± 66 versus 470 ± 60 nM). In conclusion, Ca2+ influx is necessary for a full induction of neutrophil priming by IL-8.