Functional mapping of the FcγRII binding site on human IgG1 by synthetic peptides

Receptors specific for the Fc part of IgG (FcγR) are expressed by several cell types and play diverse roles in immune responses. Impaired function of the activating and inhibitory FcγRmay result in autoimmunity. Thus, the modulation of IgG‐FcγR interaction can be a target for the development of treatments for some autoimmune and inflammatory diseases. This study addresses the localization and functional characterization of linear sequences in human IgG1 which bind to FcγRII. Peptides with overlapping sequences derived from the CH2 domain of human IgG1 between P234 and S298 were synthesized and used in binding and functional experiments. Binding of the peptides to FcγR was assayed in vitro and ex vivo, and peptides foundto interact were functionally tested. The shortest effective peptide was T256–P271, which bound to soluble recombinant FcγRIIb with Kd=6×106 M–1. The biotinylated peptides R255–P271 and T256–P271 complexed by avidin exhibited functional activity; they induced FcγRIIb‐mediated inhibition of the BCR‐triggered Ca2+ response of human Burkitt lymphoma cells, and inflammatory cytokine production (TNF‐α and IL‐6) by the human monocyte cell line MonoMac. In conclusion, our results suggest that the selected peptides functionally represent the FcγRII‐binding part of IgG1.