Hemorrhage at sites of the reverse passive Arthus reaction in platelet-depleted mice. (A) Mice were subjected to rpA () in the presence and absence of platelets and killed at 4 hours. Erythema was seen in control mice (left), while massive petechial bleeding was observed only in thrombocytopenic animals (right). Bar = 5 mm. (B) Evans blue leakage into the tissue was measured to assess the size of the inflammatory area. No differences were found between control and platelet-depleted animals. (C) Hemoglobin content in biopsies of the inflamed and control skin. Induction of the rpA, but not the IgG control, led to significantly elevated Hb levels in thrombocytopenic mice (*P < .001; n = 4). Error bars represent SEM. (D) Skin sections stained with H&E revealed accumulation of RBCs () in the inflamed skin of thrombocytopenic mice. Bar = 100 μm.