PLATELETS AND THROMBOPOIESIS Role of molecular mimicry of hepatitis C virus protein with platelet GPIIIa in hepatitis C–related immunologic thrombocytopenia

Patients with HIV-1 immune-related thrombocytopenia (HIV-1–ITP) have a unique Ab against platelet GPIIIa49-66 capable of inducing oxidative platelet fragmentation in the absence of complement. HIV-1– seropositive drug abusers are more prone to develop immune thrombocytopenia than non–drug abusers and have a higher coinfection with hepatitis C virus (HCV) than non–drug abusers (90% vs 30%). Molecular mimicry was sought by screening a phage peptide library with anti– GPIIIa49-66 antibody as bait for peptides sharing homology sequences with HCV. Several phage peptide clones had 70% homology with HCV protein. Sera from dually infected thrombocytopenic patients with HCV and HIV-ITP reacted strongly with 4 nonconserved peptides from HCV core envelope 1. Reactivity correlated inversely with platelet count (r2 0.7, P < .01). Ab raised against peptide PHC09 in GPIIIa / mice induced thrombocytopenia in wild-type mice. Affinity-purified IgG against PHC09 induced oxidative platelet fragmentation in vitro. Drug abusers dually infected with HCV and HIV-1 had a greater incidence and severity of thrombocytopenia as well as titer of anti–GPIIIa49-66/PHC09 Ab. NZB/W F1 mice injected with recombinant core envelope 1 developed Ab versus PHC09 and significantly decreased their platelet count (P < .001). Thus, HCV core envelope 1 can induce thrombocytopenia by molecular mimicry with GPIIIa49-66. (Blood. 2009;113:4086-4093)