Therapeutic intervention in HIT model. KKO (200 μg) was given intraperitoneally at baseline preceded by either intravenous heparin (100 U/kg) or protamine sulfate (2 mg/kg). Platelet counts were measured at the times noted. Subsequent therapeutic interventions at 21 and 45 hours are denoted by vertical gray arrows. (A) hPF4^mid/FcγRIIA animals. (B) hPF4^high/FcγRIIA animals. indicate animals that received only KKO; ▵, KKO plus heparin; and ♦, KKO plus protamine sulfate. At least 4 animals were studied per time point. The means ± 1 SD are shown. *P < .05 versus animals receiving KKO alone.