Cooperative stimulatory effects of tumor necrosis factor and granulocyte-macrophage colony-stimulating factor on the particular respiratory burst activity in human neutrophils: synergistic priming effect on concanavalin A-induced response, no interactive priming effect on the chemotactic peptide-induced response and additive triggering effect.

Tumor necrosis factor (TNF), granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) rapidly primed human neutrophils for enhanced superoxide (O2-) release, and membrane depolarization stimulated by chemotactic peptide (N-formyl-methionyl-leucyl-phenylalanine), interleukin 8, concanavalin A (Con A) and ionomycin. Combined stimulation of human neutrophils with the optimal concentrations of TNF plus GM-CSF showed no additive or synergistic effects according to the subsequent stimuli and within the parameters tested. Particularly, a high synergistic priming effect of these two cytokines was observed when Con A was used as a triggering agonist of O2- release. The priming of human neutrophils with the optimal concentrations of TNF plus G-CSF, however, always resulted in the same effect as TNF alone. TNF and GM-CSF triggered O2- release directly in human neutrophils for prolonged time periods, and combined stimulation of human neutrophils with the optimal concentrations of TNF plus GM-CSF triggered an added amount of O2- release. TNF and GM-CSF by themselves induced an increase in cytoplasmic pH (intracellular alkalinization), an important signaling event for functional activation of neutrophils, though combined stimulation of human neutrophils with the optimal concentrations of the two cytokines had no additive effects on cytoplasmic pH. The present results show cooperative interaction between TNF and GM-CSF in their stimulatory effects on particular functions in human neutrophils, and these synergistic effects are probably mediated via a mechanism distal to or independent of intracellular alkalinization.