Modulation of Human Neutrophil Apoptosis by Immune Complexes

Abstract

In the present study we examined whether immune complexes (IC) are able to modulate human neutrophil apoptosis. We observed different effects depending on the type of IC employed. Precipitating IC (pIC) and Ab-coated erythrocytes (E-IgG) triggered a marked stimulation of apoptosis, while heat-aggregated IgG and soluble IC, significantly delayed spontaneous apoptosis. Blocking Abs directed to Fcgamma receptor type II (FcgammaRII), but not to FcgammaRIII, markedly diminished the acceleration of apoptosis triggered by either pIC or E-IgG, supporting a critical role for FcgammaRII in apoptosis stimulation. This phenomenon, on the other hand, does not appear to involve IC phagocytosis or the participation of CR3. Acceleration of neutrophil apoptosis triggered by either pIC or E-IgG seems to require the activation of the respiratory burst, as suggested by 1) the ability of catalase to prevent apoptosis stimulation; 2) the effect of azide, an heme enzyme inhibitor, which dramatically enhanced apoptosis induced by pIC or E-IgG; and 3) the inability of pIC or E-IgG to accelerate apoptosis of neutrophils isolated from CGD patients. It is well established that IC affect the course of inflammation by inducing the release of inflammatory cytokines, proteolytic enzymes, oxidative agents, and other toxic molecules. Our results suggest that IC may also affect the course of inflammation by virtue of their ability to modulate neutrophil apoptosis.