Effect of monocyte depletion on platelet count and thrombosis in the HIT model. (A) Platelet counts after induction of HIT in the FcγRIIA⁺/hPF4⁺ mice model. Clodronate- or PBS-laden liposomes were injected intravenously. Twelve hours later (Time 0), KKO 2.5 mg/kg was administered intraperitoneally. The first platelet count was measured 4 hours later. Animals receiving no liposomes (○) or PBS-laden liposomes (▩) had modest thrombocytopenia compared with the same mice receiving clodronate-laden liposomes (♦). N ≥ 3, each in duplicate. Mean ± 1 SE are shown. *P < .05 for platelet drop after KKO in mice with depleted monocytes versus control mice. (B) Same as panel A but animals received NaCl (open symbols) or GdCl₃ (black symbols) 32 hours prior to the KKO 10 mg/kg intraperitoneal injection (diamonds) or controls without KKO (circles). N ≥ 3, each in duplicate. Mean ± 1 SE are shown. *P < .05 for platelet drop in mice treated with GdCl³ followed by KKO versus mice treated with NaCl followed by KKO. (C) Times to complete occlusion in a photochemical carotid artery model in FcγRIIA⁺/hPF4⁺ mice under conditions noted in the figure are shown as mean ± 1 SE. The platelet counts at the time of study are indicated above each bar and is per 10⁹/mL. N values are noted in the figures. *P < .001 for time to occlusion relative to mice not receiving either KKO or liposomes.