VCAM-1⁺, F4/80^hibone marrow macrophages ingest transfused old RBCs. (A) Gating strategy for identifying bone marrow macrophages (VCAM-1⁺, F4/80^hi, CD11b^lo) that phagocytose transfused RBCs (GFP⁺). (B) Frequency of phagocytosis of old RBCs at 2 hours posttransfusion by bone marrow macrophages, Ly6C^hi monocytes and granulocytes; although macrophages ingest some transfused RBCs, no such phagocytosis is seen with Ly6C^hi monocytes or granulocytes. (C-D) Frequency of ingested GFP⁺ RBCs at 2 and 24 hours posttransfusion in circulating Ly6C^hi monocytes and granulocytes. Data representative of 3 experiments with at least 3 mice per group. *P < .05; ANOVA with Tukey or Sidak multiple comparison test. ns, not significant.