Effect of recombinant HCV core envelope 1 injection on mouse platelet counts. NZB/W F1 mice were challenged with multiple control (A) or rHCV core envelope 1 (B) injections. At 90 days, the platelet count had decreased in 8 of 8 NZB/W F1 mice (x-axis: b and a refer to before and after immunization, respectively; n = 8, P < .001) (B). No decrease in platelet count was found in the comparison group immunized with control protein (A). The serum titer to peptide PHC09 was elevated in NZB/W F1 mice immunized with rHCV core envelope 1 (HCV; C), whereas the control protein (control) had no effect. (D) Correlation between percentage platelet count decrease and serum titer versus PHC09 in NZB/W F1 mice. Percentage platelet decrease correlated inversely with serum titer versus PHC09 (r² = 0.63, n = 16, P < .05). · and ○ refer to NZB/W F1 mice immunized with rHCV core envelope 1 or control protein, respectively. (E) In vivo induction of thrombocytopenia in mice injected with affinity-purified anti-PHC09 IgG derived from NZB/W F1 mice immunized with rHCV core envelope 1. Purified control mouse IgG (Ctl IgG), and mouse IgG against PHC09 (HCV IgG; 25 μg/mouse) were injected intraperitoneally into Balb/c mice (n = 4 per group). SEM is given.