title: Antibodies causing thrombocytopenia in patients treated with RGD-mimetic platelet inhibitors recognize ligand-specific conformers of αIIb/β3 integrin.
abstract: Arginine-glycine-aspartic acid (RGD)-mimetic platelet inhibitors act by occupying the RGD recognition site of α(IIb)/β(3) integrin (GPIIb/IIIa), thereby preventing the activated integrin from reacting with fibrinogen. Thrombocytopenia is a well-known side effect of treatment with this class of drugs and is caused by Abs, often naturally occurring, that recognize α(IIb)/β(3) in a complex with the drug being administered. RGD peptide and RGD-mimetic drugs are known to induce epitopes (ligand-induced binding sites [LIBS]) in α(IIb)/β(3) that are recognized by certain mAbs. It has been speculated, but not shown experimentally, that Abs from patients who develop thrombocytopenia when treated with an RGD-mimetic inhibitor similarly recognize LIBS determinants. We addressed this question by comparing the reactions of patient Abs and LIBS-specific mAbs against α(IIb)/β(3) in a complex with RGD and RGD-mimetic drugs, and by examining the ability of selected non-LIBS mAbs to block binding of patient Abs to the liganded integrin. Findings made provide evidence that the patient Abs recognize subtle, drug-induced structural changes in the integrin head region that are clustered about the RGD recognition site. The target epitopes differ from classic LIBS determinants, however, both in their location and by virtue of being largely drug-specific.
authors.affiliation: Blood Research Institute, BloodCenter of Wisconsin, Milwaukee, WI 53201, USA. dan.bougie@bcw.edu
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Bougie
authors.forename: Mark
authors.initials: M
authors.lastname: Rasmussen
authors.forename: Jieqing
authors.initials: J
authors.lastname: Zhu
authors.forename: Richard H
authors.initials: RH
authors.lastname: Aster
mesh_terms: D000818:Animals; D000906:Antibodies / Q000009:adverse effects* / Q000276:immunology / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D000077542:Eptifibatide; D006801:Humans; D008024:Ligands; D051379:Mice; D008807:Mice, Inbred BALB C; D008954:Models, Biological; D009842:Oligopeptides / Q000737:chemistry / Q000276:immunology; D010455:Peptides / Q000627:therapeutic use; D010975:Platelet Aggregation Inhibitors / Q000737:chemistry / Q000627:therapeutic use; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D011485:Protein Binding / Q000276:immunology; D011487:Protein Conformation; D051381:Rats; D013379:Substrate Specificity; D013921:Thrombocytopenia / Q000188:drug therapy / Q000209:etiology* / Q000276:immunology; D000077466:Tirofiban; D014443:Tyrosine / Q000031:analogs & derivatives / Q000627:therapeutic use
chemical_list: D000906:Antibodies; D008024:Ligands; D009842:Oligopeptides; D010455:Peptides; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; C047981:arginyl-glycyl-aspartic acid; D000077466:Tirofiban; D000077542:Eptifibatide