Macrophage phagocytosis of Ox-RBCs is dependent on serum and SRs. Phagocytosis of Cu/ascorbate-treated Ox-RBCs (), or PBS-treated RBCs (□), by RPM (A), or bone marrow–derived macrophages (B). (C) Phagocytosis of Ox-RBCs by RPM is strongly inhibited in the absence of FCS. (D) Macrophage phagocytosis of Ox-RBCs is inhibited by the SR ligands dextran sulfate (100 μg/mL), fucoidan (100 μg/mL), carrageenan (100 μg/mL), and poly-I (50 μg/mL), but not by the non-SR ligands poly-A (50 μg/mL), poly-C (50 μg/mL), or chondroitin sulfate (100 μg/mL). (E) Functional blocking antibodies to SR-A or CD36 (25 μg/mL) do not inhibit phagocytosis of Ox-RBCs by RPM. (F) Phagocytosis of Ox-RBCs is not affected in the presence of 10% IgG-depleted FCS. In panels D-F, control refers to incubation in DMEM with 10% FCS. In phagocytosis experiments, RBCs were incubated with adherent macrophages for 60 minutes at 37°C. Following lysis of noningested RBCs and fixation/staining, the number of ingested RBCs was counted in 200 to 300 macrophages per coverslip and expressed as a phagocytosis index (number of ingested RBCs/100 macrophages). Data are mean plus or minus SEM for 3 to 6 separate experiments. *P < .05 and **P < .01, compared with control, using the Student t test for paired comparisons.