Mechanisms involved in the binding of IgG immune complexes to sections of inflamed gingiva

The binding of particulate (sensitized sheep erythrocytes= EA) and soluble (horse radish peroxidase (HRP)‐anti‐HRP) IgG immune complexes to cryostat sections of inflamed human gingiva was studied. EA bound preferentially to inflammatory cell infiltrates in all biopsy specimens, and HRP‐anti‐HRP complexes were found to bind to the surface of mononuclear cells. Binding of EA was abolished by treatment of cryostat sections with 1 mM periodic acid (30 min) or 4% formaldehyde (10 min). Binding was also abolished by exposure of sections to cold ethanol for 5 min. No binding of fluorescein labelled, heat aggregated human IgG to sections of washed and ethanol‐fixed biopsies of inflamed human gingiva was observed. Results of inhibition experiments with rabbit and human native or heat aggregated IgG, rabbit and human IgG Fc and IgG F(ab′)2 fragments, human IgG 1 and IgG2, mildly reduced and alkylated human IgG and with rabbit anti‐human Clq, indicated that the binding is not due to activated C1 or to the presence of rheumatoid factors. Our findings are consistent with the concept that the binding is due to the presence of IgG Fc receptors (IgGFcR) on mononuclear cells. Ethanol fixation of specimens compromises any conclusions regarding IgGFcR activity in the tissues.