ANTIIDIOTYPIC ANTIBODIES AGAINST AN ANTIBODY TO THE PLATELET GLYCOPROTEIN (GP) IIB-IIIA COMPLEX MIMIC GP IIB-IIIA BY RECOGNIZING FIBRINOGEN

作者：ABRAMS CS; RUGGERI ZM; TAUB R; HOXIE JA; NAGASWAMI C; WEISEL JW; SHATTIL SJ

来源：Journal of Biological Chemistry, 1992, 267(4): 2775-2785.

Binding of the adhesive ligand fibrinogen and the monoclonal antibody PAC1 to platelet glycoprotein (GP) IIb-IIIa is dependent on cell activation and inhibited by Arg-Gly-Asp (RGD)-containing peptides. Previously, we identified a sequence in a hypervariable region of PACI (mu-CDR3) that mimics the activity of the antibody. Here we examine whether monoclonal antibodies to this idiotypic determinant in PAC1 can mimic GP IIb-IIIa by binding to fibrinogen. Mice were immunized with a peptide derived from the mu-CDR3 of PAC1. Four antibodies were obtained that recognized fibrinogen as well as a recombinant form of the variable region of PAC1. However, they did not bind to other RGD-containing proteins, including von Willebrand factor, fibronectin, and vitronectin. Several studies suggested that these anti-PAC1 peptide antibodies were specific for GP IIb-IIIa recognition sites in fibrinogen. Three such sites have been proposed: two RGD-containing regions in the A-alpha-chain, and the COOH terminus of the gamma-chain (gamma-400-411). Two of the antibodies inhibited fibrinogen binding to activated platelets, and all four antibodies bound to the fibrinogen A-alpha-chain on immunoblots. Antibody binding to immobilized fibrinogen was partially inhibited by monoclonal antibodies specific for the two A-alpha-chain RGD regions. However, the anti-PAC1 peptide antibodies also bound to plasmin-derived fibrinogen fragments X and D100, which contain gamma-400-411 but lack one or both A-alpha(RGD) regions. This binding was inhibited by an antibody specific for gamma-400-411. When fragment D100 was converted to D80, which lacks gamma-400-411, antibody binding was reduced significantly (p < 0.01). Electron microscopy of fibrinogen-antibody complexes confirmed that each antibody could bind to sites on the A-alpha and gamma-chains. These studies demonstrate that certain anti-PAC1 peptide antibodies mimic GP IIb-IIIa by binding to platelet recognition sites in fibrinogen. Furthermore, they suggest that the gamma-400-411 region of fibrinogen may exist in a conformation similar to that of an A-alpha(RGD) region of the molecule.

• 出版日期1992-2-5