Characterization of an FcγRI-binding peptide selected by phage display

Abstract

The high-affinity IgG receptor, Fcγ receptor I (FcγRI), is expressed exclusively on myeloid cells, and there is a great interest in the targeting of vaccine antigens to FcγRI using anti-human FcγRI antibodies or fragments derived from such molecules. In order to reduce the size and complexity of the targeting reagent, we have searched for FcγRI binding peptides in peptide libraries displayed on phage. The human monocytic cell line U937 was used as target. Phages that displayed the consensus peptide CLRSGXGC were selected and revealed increased binding to IFN-γ stimulated versus non-stimulated U937 cells as well as to FcγRI transfected versus non-transfected IIA1.6 cells. Furthermore, they bound the extracellular domains of soluble FcγRI, but neither FcγRIIA, FcγRIIB nor FcγRIIIB. Binding was inhibited by a synthetic version of the peptide, whereas neither human IgG nor the FcγRI-specific monoclonal antibodies (mAb) mAb22 and 32.2 interfered. Flow-cytometry analysis and internalization studies showed that a synthetic biotin-conjugated peptide ADGACLRSGRGCGAAK-bio was able to target U937 cells and FcγRI transfected IIA1.6 cells, and further to promote internalization and vesicular degradation of streptavidin coupled to 1 μm magnetic beads. These peptides may have potential as FcγRI targeting reagents. © The Author 2006. Published by Oxford University Press. All rights reserved.