Gene-dose effect of CD47 on inhibition of FcγR-mediated phagocytosis of Ox-RBCs. Ox-RBCs from WT (□), CD47^+/− (), or CD47^−/− (■) mice were opsonized with mAb 34-3C, washed, and incubated with RPM in the presence or absence of 10% FCS for 30 minutes at 37°C. Following lysis of uningested RBCs, phagocytosis was determined as described in the legend to Figure 1. Equal opsonization was confirmed following labeling of opsonized RBCs with anti–mouse IgG FITC, using flow cytometry, showing the following mean fluorescence intensity (MFI) values: WT Ox-RBCs = 135.1, CD47^+/− Ox-RBCs = 134.0, and CD47^−/− Ox-RBCs = 134.4. Data are mean plus or minus SEM for 4 separate coverslips per group in one representative experiment. *P < .05; **P < .01; and ***P < .001, using the Student t test for paired comparisons. ns indicates not significant.