Drug-induced thrombocytopenia: localization of the binding site of GPIX-specific quinine-dependent antibodies

Abstract

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 quininedependent 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 GPIb␣ and GPIb␤ 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

Drug-induced thrombocytopenia: MIBS trumps LIBS

“…4 Although the introduction of RIC regimens has resulted in a decrease in the high incidence of TRM associated with myeloablative conditioning, an intense debate is currently ongoing regarding the question of whether patients should be subjected to the substantial morbidity, especially graft-versushost disease (GVHD), and the risk of mortality associated with RIC allo-SCT as part of first-line therapy compared with the relatively safe procedure of auto-SCT. [5][6][7][8][9][10][11] Lokhorst et al performed a donor versus no-donor analysis of patients included in the phase 3 HOVON-50 MM trial. 1 After a single auto-SCT, eligible patients were randomized according to the availability of an HLA-identical sibling to receive either maintenance therapy consisting of thalidomide or ␣-interferon or RIC allo-SCT after low-dose 2 Gy total body irradiation.…”

“…In contrast, different mechanisms have been described for other immune drug-induced thrombocytopenias. 3,7,8 Here, Bougie and colleagues directly investigated this issue and found that patient antibodies did not recognize LIB determinants as previously expected but instead recognized conformational changes in ␣ IIb ␤ 3 induced by the drug. 1 In the majority of patients with eptifibatide-and tirofiban-induced thrombocytopenia (30 of 43 patients), antibody binding was drug specific and only occurred when the For personal use only.…”

Flow cytometry in the diagnosis of drug‐induced thrombocytopenia: Two illustrative cases

“…This might be particularly true for flow cytometry, because of its wide availability in clinical laboratories and its potential suitability to identify several different drugs. The only comparison between flow cytometry and MAIPA for detecting quininedependent antibodies in 13 patients showed a lower sensitivity of flow cytometry [11], and thus MAIPA remains the gold standard test.…”

“…Drug binding to platelet surface can form a new epitope or cause the exposure of a neo-epitope. Glycoprotein Ib-IX and GP IIb/IIIa are most frequently involved in drug binding, which leads to the formation of new epitopes that appear to be very specific for each different drug [6][7][8][9][10][11][12][13][14]. The development of drug-dependent antiplatelet antibodies may thus cause accelerated platelet clearance in vivo and induce severe thrombocytopenia.…”

“…An immunological mechanism is postulated for many drugs, but so far there is clear evidence of drugdependent antiplatelet antibodies only for a few of them (rifampicin, abciximab, quinine, ranitidine, vancomycin, teicoplanin, sulfonamide, tamoxifene, heparin, and few others) [2,[6][7][8][9][10][11][12][13][14][15][16]. Drug binding to platelet surface can form a new epitope or cause the exposure of a neo-epitope.…”