STIMULATION OF INTRACELLULAR CA2-COMPLEXES - FUNCTIONAL ACTIVATION OFFC-GAMMA-RIIIB DURING PRIMING( LEVELS IN HUMAN NEUTROPHILS BY SOLUBLEIMMUNE)

Soluble immune complexes bind to unprimed neutrophils and generate int racellular Ca2+ transients but fail to activate the NADPH oxidase. Fol lowing priming of the neutrophils with either tumor necrosis factor al pha of granulocyte-macrophage colony-stimulating factor, stimulation o f the cells with the soluble immune complexes leads to an enhanced Ca2 + signal and significant secretion of reaction oxidants. The enhanced Ca2+ signal observed in primed neutrophils results from the influx of Ca2+ from the external environment and is partly sensitive to tyrosine kinase inhibitors. This is in contrast to the Ca2+ signal observed in unprimed neutrophils, which arises from the mobilization of intracell ular stores. When the surface expression of Fc gamma RIIIb on primed n eutrophils was decreased wither through incubation with Pronase of pho sphoinositide-specific phospholipase C, the extra enhanced Ca2+ mobili zation seen in primed cells was significantly lowered, while the initi al rise in intracellular Ca2+ was unaffected. Depletion of Fc gamma RI IIb had no significant effect on the Ca2+ transients in unprimed neutr ophils. Cross-linking Fc gamma RII, but not Fc gamma RIIIb, induced in crease in intracellular Ca2+ in unprimed neutrophils, while cross-link ing either of these receptors increased Ca2+ levels in primed neutroph ils. The Fc gamma RII-dependent intracellular Ca2+ rise in primed cell s was unaffected by incubation in Ca2+-free medium, whereas the Fc gam ma RIIIb-dependent transient was significantly decreased when Ca2+ inf lux was prevented in Ca2+-free medium supplemented with EGTA. Cross-li nking wither Fc gamma RII or Fc gamma RIIIb in primed or unprimed cell s failed to stimulate substantial levels of inositol 1,4,5-trisphospha te production. These results indicate that following stimulation of pr imed neutrophils with soluble immune complexes the enhanced Ca2+ mobil ization observed is the result of a functional activation of the glyco sylphosphatidylinositol-linked Fc gamma RIIIb.