Complement-dependent inhibition of degradation of soluble immune complexes and immunoglobulin aggregates by thioglycollate-stimulated peritoneal macrophages.

Previous studies have shown that the degradation of soluble immune complexes or aggregates (AIgG) by normal peritoneal macrophages can be enhanced by complement. The enhancement of degradation was shown to be at least in part dependent on the number of C3b molecules bound per complex. The present investigations indicate that the enhanced degradation is not found with thioglycollate-stimulated macrophages, and that at high concentrations of complement, inhibition may even occur. The Fc receptor-mediated degradation of soluble immune complexes and AIgG by stimulated macrophages was at least twice as high as that by normal macrophages. This increase was compatible with the increased number of Fc receptors on the stimulated macrophages. The inhibitory effect of high concentrations of serum, as a complement source, on the degradation of AIgG was dependent on the number of C3b molecules bound per AIgG. Although there was also a two-fold increase in the number of C3b receptor sites on the stimulated macrophages, more than 11 C3b molecules per AIgG40 caused significant inhibition of degradation. This phenomenon may be dependent on shielding of Fc-Fc receptor interaction by varying numbers of C3b molecules per complex.