CD47 concentration on normal and 4.2-deficient RBCs. (A) Fluorescence image intensity analysis of 4.2-Nippon RBCs (n = 60 each) labeled with 6H9 shows a mean CD47 level that is 17% of normal with significant variation among both normal and 4.2-Nippon cells. (B) FC measures of CD47 expression for 2 homozygous RhD (R2R2), 2 heterozygous RhD (R2r or R1r), and 4 RhD-negative RBC samples. CD47 levels for R2R2 and Rh-negative RBCs are statistically different (P < .001). Cells were stained with the antibodies F8D8 (RhD) or BRIC 126 (CD47) and a fluorophore-conjugated antihuman or antimouse secondary antibody.