Drug-induced thrombocytopenia: localization of the binding site of GPIX-specific quinine-dependent antibodies.
Immune thrombocytopenia is a common complication of therapy with a large number of drugs. The most widely studied drug-induced immune thrombocytopenia (DIT) is caused by quinine. In most cases of DIT, antibodies bind to the platelet membrane glycoprotein (GP) Ib-IX complex in a drug-dependent fashion and bring about increased platelet clearance by the reticuloendothelial system resulting in thrombocytopenia. Here, we report the characterization of the quinine-dependent antibody activity of sera from 13 patients with quinine-induced thrombocytopenia. In our series of patients, GPIX was the most prevalent target of quinine-dependent antibodies. To identify the structural determinants of GPIX recognized by quinine-dependent antibodies, 4 chimeric mouse/human GPIX constructs and stable Chinese hamster ovary (CHO) cell lines that expressed the chimeras in association with GPIbalpha and GPIbbeta were produced. The analysis of 6 patient sera with the chimeric cell lines provided evidence for localization of the anti-GPIX quinine-dependent antibody binding site to the C-ext region (amino acid [aa] 64-135) of human GPIX. Further characterization of the C-ext region of the GPIX indicated that replacement of the Arg110 and Gln115 of the human GPIX with the corresponding residues from mouse (Gln and Glu, respectively) resulted in a significant reduction in the binding of GPIX antibodies in our series of patients, with Arg110Gln, giving a more pronounced effect than Gln115Glu. Hence, these 2 residues, particularly Arg110, play an important role in the structure of the antigenic site on GPIX recognized by anti-GPIX antibodies.
Department of Medicine, St George Clinical School, Level 2, Pitney Bldg, St George Hospital, Short St, Kogarah, NSW 2177, Australia.
Parisa
P
Asvadi
Zohra
Z
Ahmadi
Beng H
BH
Chong
D000293:Adolescent; D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000918:Antibody Specificity; D000962:Antimalarials / Q000009:adverse effects* / Q000276:immunology; D001665:Binding Sites / Q000276:immunology; D001792:Blood Platelets / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D008969:Molecular Sequence Data; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D011803:Quinine / Q000009:adverse effects* / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000962:Antimalarials; D019038:Platelet Glycoprotein GPIb-IX Complex; D011993:Recombinant Fusion Proteins; D011803:Quinine