Independent Effects of IgG and Complement upon Human Polymorphonuclear Leukocyte Function

Abstract

Particle ingestion by polymorphonuclear leukocytes (PMN) is promoted by cell surface recognition and binding of fragments of the third component of complement (C3) and Fc regions of certain immunoglobulin (IgG) molecules. In order to determine the influence of these specific ligand-surface membrane interactions upon other PMN functions, we have employed nonphagocytosable particles (serum-treated Sepharose beads) coated with fragments of C3 and/or IgG, and have investigated whether these provide a sufficient stimulus for the metabolic changes and degranulation that ordinarily accompany phagocytosis by PMN. Sepharose 4B activates complement in fresh normal serum and consequently is coated with fragments of C3 (confirmed by immunoelectrophoretic evidence of factor B and C3 conversion and by immunofluorescence). Adsorbed IgG could be removed from serum-treated Sepharose by boiling in 2 M NaCl without significantly influencing bound complement. We have found that normal human PMN recognize and adhere to Sepharose beads coated with fragments of C3 and consequently are stimulated to increase their oxidative metabolism (measured as superoxide anion generation). This PMN response occurred in the absence of IgG but could be amplified if this immunoglobulin was also present on the bead surfaces. Both adherence and metabolic stimulation could be blocked by treatment of the beads with F(ab′)₂ anti-C3. In contrast to metabolic stimulation, degranulation (selective extracellular release of lysosomal constituents) was observed only when PMN encountered both C3 fragments and IgG on the beads. This response could be blocked by treating beads with either F(ab′)₂ anti-C3 or F(ab′)₂ anti-IgG. These results indicate that cell surface stimulation of PMN is not an “all or none” phenomenon and that certain vital functions of these cells may be mediated or modulated independently by immunoglobulins and complement.