Macrophages are necessary for hFcγRI-dependent thrombocytopenia. (A) hFcγRI^tg 5KO (black) or 5KO (gray) mice were pretreated with the indicated reagents before being injected intravenously with antiplatelet mAb (α-PLA). Platelet counts were acquired in blood at the indicated times presented as curves (left) or at t = 4 hours presented as histograms (right) after α-PLA injection (n = 3). (B) hFcγRI^tg 5KO mice were pretreated with the indicated reagents and platelet counts acquired in the blood at t = 4 hours after α-PLA injection (n = 3). (C-E) 5KO mice (small histograms in insets) or anti-FcγRIV–treated hFcγRI^tg 5KO mice (large histograms, left in each panel) were pretreated with the indicated reagents or splenectomized when indicated and platelet counts were acquired in the blood at t = 4 hours after α-PLA injection (C-D: n = 3; E: n ≥ 3). Data are representative of at least 2 independent experiments and are represented as means ± SEM.