The binding epitopes of human CD16 (Fc gamma RIII) monoclonal antibodies. Implications for ligand binding.
Numerous mAbs have been generated against Fc gamma RIII (CD16), the low-affinity receptor for the Fc part of IgG. Most of the mAbs recognize both the receptor isoforms, transmembranous Fc gamma RIIIA, and glycosylphosphatidylinositol-linked Fc gamma RIIIB. Binding epitopes of some of the mAbs that differentiate between the two neutrophil Ag (NA) alleles of Fc gamma RIIIB (CLB-Gran11 against NA1; GRM1, BL-LGL/1 against NA2 allele) have been mapped on the first, membrane-distal domain of CD16. We demonstrate that mAbs 3G8, B88-9, CLB-Gran1, MEM-154, and LNK16 almost completely block the receptor's interaction with IgG. Using chimeric Fc gamma RIIIB/Fc epsilon RI receptors and molecular modeling, we localized the epitopes of 3G8 and B88-9 on the putative FG loop of the membrane-proximal Ig-like domain, which we have previously identified as the major binding site for IgG. The epitopes of CLB-Gran1 and MEM-154 are shown to reside in proximity to the FG loop (probably BC or C'E loop). The blocking mAb LNK16 was detected to be directed against the putative C' beta-sheet of the membrane-proximal domain, suggesting that additional residues may be involved in IgG binding of Fc gamma RIII.
Tamm
A
A
Department of Clinical Immunology, Hannover Medical School, Germany.
Schmidt
R E
RE
D000911:Antibodies, Monoclonal / Q000276:immunology*; D018076:DNA, Complementary / Q000235:genetics; D000939:Epitopes / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D007074:Immunoglobulin G / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D017452:Receptors, IgG / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000276:immunology
D000911:Antibodies, Monoclonal; D018076:DNA, Complementary; D000939:Epitopes; D007074:Immunoglobulin G; D008024:Ligands; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins