THE GLYCOSYLPHOSPHATIDYLINOSITOL-LINKED FC-GAMMA RECEPTOR-III REPRESENTS THE DOMINANT RECEPTOR STRUCTURE FOR IMMUNE-COMPLEX ACTIVATION OF NEUTROPHILS

Polymorphonuclear neutrophils (PMN) express constitutively two low-affinity Fc-gamma receptors, Fc-gamma-RII and Fc-gamma-RIII. Fc-gamma-RII is a transmembrane molecule, and Fc-gamma-RIII is linked via a glycosylphosphatidylinositol (GPI) anchor to the membrane. The role of each of these receptors in activation of PMN is still unclear. We used specific cross-linking of Fc-gamma-RII via Fab fragments of IV.3 (anti-Fc-gamma-RII, CDw32) and of Fc-gamma-RIII using F(ab')2 fragments of 3G8 (anti-Fc-gamma-RIII, CD16) to activate PMN. Stimulation of Fc-gamma-RIII was significantly more effective in inducing a respiratory burst than cross-linking of Fc-gamma-RII. A synergistic effect was observed after simultaneous activation of Fc-gamma-RIII. We could demonstrate that both Fc-gamma-R mobilize calcium as intracellular signal in spite of their different membrane linkage. The kinetic of calcium mobilization after Fc-gamma-R stimulation is delayed in comparison to formyl-methionyl-leucyl-phenylalanine activation. In addition Fc-gamma-R induced increase of cytoplasmic calcium is pertussis toxin insensitive. When monoclonal IgG1-aleph complexes were used for stimulation calcium mobilization and hydrogen peroxide (H2O2) production could also be demonstrated. Inhibition studies of this activation using monoclonal antibodies suggested that this immune complex activation was predominantly mediated via Fc-gamma-RIII. Only in Fc-gamma-RIII-deficient PMN from paroxysmal nocturnal hemoglobinuria patients could a decreased H2O2 production be demonstrated to be Fc-gamma-RII dependent. In normal PMN the GPI-anchored Fc-gamma-RIII structure is the predominant receptor.