Inhibition of anti–GPIIIa49-66 Ab-induced oxidative platelet fragmentation by HCV peptides. (A) Effect of HCV peptides on anti–GPIIIa49-66 platelet reactivity. Patient IgG was preincubated with different peptides prior to incubation with gel-filtered platelets. CAPESIEF refers to positive control (CAPESIEFPVSEARVLED). Irrel refers to irrelevant peptide. , , □, ■ refer to molar Ab/peptide ratios of 1:100, 1:10, 1:5, and 1:2, respectively. Effect of IgG against HCV peptide (PHC09) on (B) platelet fragmentation and (C) oxidation. Affinity-purified IgG from 5 HIV-1/HCV-ITP patients with high reciprocal Ab titer to PHC09-induced platelet fragmentation (B) and oxidation (C) in vitro. C (□) indicates control human IgG; P (■), HIV-1-ITP patient IgG; and IVDA horizontal line, affinity purified anti-HCV peptide PHC09 IgG from dually infected drug abusers. The ■, , □ refer to doubling dilutions of isolated IVDA IgG (25, 12.5, and 6.25 μg/mL, respectively). (D) Presence of platelet fragments in patients with HCV-ITP. Immunoblots of serum immune complexes run on SDS-PAGE and immunoblotted with anti–GPIIIa49-66. (E) Effect of HCV IgG isolated from HCV immune complexes on (E) platelet fragmentation and (F) platelet DCFH oxidation. Pt refers to patient. ■, , refer to serial 1:2 dilutions of IgG, starting at 50 μg/mL. SEM is given.