Quantitative studies of Fc receptors on human monocytes: characterization by binding of homologous and heterologous monomeric IgG and soluble immune complexes of different composition.
The binding of 125I-labelled monomeric human and rabbit IgG (H-IgG, R-IgG) and rabbit IgG immune complexes (IC) to monocyte-enriched human peripheral blood cells had been investigated quantitatively. Scatchard plots at 4 degrees demonstrated that R-IgG bound to the same number of Fc receptors per cell (19,000) as H-IgG, but with a lower affinity (2.4 +/- 0.9 X 10(8)/l/mol and 3.5 +/- 1.1 X 10(8)l/mol, respectively). Inhibition studies demonstrated that the two ligands could mutually inhibit each other, H-IgG having higher inhibitory efficiency versus R-IgG than the reverse. It seems likely that R-IgG reacts with the Fc receptor for the homologous IgG, although with lower affinity. Binding of soluble R-IgG anti-bovine serum albumin (BSA) IC, prepared at molar antigen:antibody (Ag:Ab) ratio of 2:1 and 12:1, showed quite different behaviour, the IC binding with association constants almost 10-fold lower than the affinity of monomeric R-IgG, but binding six- to seven-fold as many IgG molecules per cell at saturation.
D000818:Animals; D000936:Antigen-Antibody Complex / Q000378:metabolism*; D001667:Binding, Competitive; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D008970:Molecular Weight; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism; D011817:Rabbits; D011961:Receptors, Fc / Q000032:analysis*; D012710:Serum Albumin, Bovine / Q000276:immunology; D013045:Species Specificity
D000936:Antigen-Antibody Complex; D007074:Immunoglobulin G; D011961:Receptors, Fc; D012710:Serum Albumin, Bovine