CD47 on Ox-RBCs effectively inhibits FcγR-mediated phagocytosis. Untreated RBCs or Ox-RBCs from WT mice (□) or CD47^−/− mice (■) were opsonized with mAb 34-3C, washed, and incubated with RPM (A) in the presence of 10% FCS, or (B) in the absence of FCS for 30 minutes at 37°C. Following lysis of uningested RBCs, phagocytosis was determined as described in the legend to Figure 1. Data are mean plus or minus SEM for 4 separate coverslips per group in one representative experiment of 3. Untreated WT RBCs (C), untreated CD47^−/− RBCs (D), WT Ox-RBCs (E), and CD47^−/− Ox-RBCs (F) were analyzed by flow cytometry to confirm equal opsonization, using FITC anti–mouse IgG. *P < .05; **P < .01; and ***P < .001, using the Student t test for paired comparisons. ns indicates not significant.