Human neutrophil aggregation and increased adherence to human endothelial cells induced by heat-aggregated IgG and immune complexes.

Several types of IgG-dependent phagocytic stimuli independent of complement were investigated for their property to induce human polymorphonuclear neutrophil leucocyte (PMN) aggregation and adherence to human endothelial cells (EC) in culture. A Coulter counter method was employed for the detection of cell aggregation. Aggregated IgG, ovalbumin-anti-ovalbumin (OV anti-OV) immune complexes (both insoluble and soluble) and opsonized latex particles induced a significant degree of PMN aggregation which was detectable as early as 2 min after exposure of PMN to these stimuli. This aggregation was dependent on divalent cations (Ca++, Mg++). The same phagocytic stimuli furthermore significantly increased adherence of PMN to cultured human EC and serum-coated plastic. Controls consisting of native IgG, and OV anti-OV complexes prepared from Fab')2 antibody failed to induce either aggregation or increased adherence of PMN. These data suggest that exposure of PMN to IgG-dependent phagocytic stimuli induces increased adhesiveness of PMN and that interaction between the Fc-receptor of PMN and the Fc-portion of phagocytic stimuli is essential for this effect.