KKO-induced thrombocytopenia in hPF4 mice. (A) Platelet counts in mice after intraperitoneal injection of KKO. The first time point is at 3 hours after injection. Filled circles indicate hPF4^high mice, 200 μg KKO; and open circles, FcγRIIA transgenic mice, 200 μg KKO. Diamonds indicate hPF4^high/FcγRIIA double-transgenic mice. Open diamonds, light gray diamonds, dark gray diamonds, and filled diamonds indicate 50, 100, 200, and 400 μg KKO intraperitoneally, respectively. The mean of 3 experiments, each performed in triplicate, is shown. (B) Animals were all hPF4^high/FcγRIIA double-transgenic mice. ○ indicates 200 μg TRA, intraperitoneally; ♦, 200 μg RTO, intraperitoneally; and •, 200 μg KKO, intraperitoneally. The mean ± 1 SD of 3 experiments, each in triplicate is shown. *P < .05 (C) All animals received 200 μg KKO. • indicates hPF4^high mice, 200 μg KKO; ○, FcγRIIA transgenic mice, 200 μg KKO; ⋄, hPF4^low/FcγRIIA; , hPF4^mid/FcγRIIA; and •, hPF4^high/FcγRIIA. The mean ± 1 SD of 3 experiments, each performed in triplicate, is shown. *P < .05 from baseline value. (D) All animals received 200 μg KKO, intraperitoneally. • indicates hPF4^high mice, 200 μg KKO; , hPF4^mid mice; and •, hPF4^mid mice that also received 20 U heparin subcutaneously daily for 4 days as indicated by arrows. The mean ± 1 SD of 3 experiments, each performed in triplicate, is shown. *P < .05 of heparin treated from untreated hPF4^mid/FcγRIIA mice.