INTERFERON-GAMMA AFFECTS PROTEIN-KINASE-C ACTIVITY IN HUMAN NEUTROPHILS

Interferon-gamma (IFN-gamma) is a priming agent of polymorphonuclear neutrophilic granulocyte (PMN) oxygen metabolism, and protein kinase C (PKC) is traditionally believed to play a central role in activation of this oxygen metabolism, In the present study, we have shown that the PKC activity in PMN is affected by IFN-gamma. After only 2 minutes exposure to IFN-gamma (100 U/ml), PKC activity was significantly increased in the noncytosolic fraction of the cells, This increase was transient, but toward the end of the priming period of 2 h, the membrane-associated PKC activity increased again to about 152% of control, In the cytosolic fraction, a small and hardly detectable decrease in PKC activity was observed, Treatment of PMN with granulocyte-macrophage colony-stimulating factor (GM-CSF), another PMN priming agent, showed no signficant effects on the PKC activity, When the cells were stimulated with the bacterial peptide fMLP after a priming period with IFN-gamma or GM-CSF for 2 h, no significant difference between treated and control cells could be observed. PMN oxygen metabolism, measured by flow cytometry as an accumulation of the fluorescent compound dichlorofluorescein, was in these experiments significantly primed by IFN-gamma, both at baseline and when stimulated with fMLP, The protein kinase C inhibitors H7 and Ro31-8220 blocked the fMLP responses to some extent, but not completely, However, no significant difference between fMLP responses in control and IFN-gamma-treated cells could be detected after administration of inhibitors. Our data therefore show that IFN-gamma affects the PKC activity in human PMN and that PKC probably play some role in the IFN-gamma priming of PMN oxygen metabolism,