Differential binding patterns of 3 Siaα2-6–binding proteins to RBCs. RBCs from 9 human volunteers with blood types A, B, and O (3 from each group) were incubated with subagglutinating concentrations of Siglec-2-Fc-QDs, 1918SC-QD complex, or biotinylated SNA, followed by streptavidin-conjugated QDs. (A,C) Binding density of Siglec-2-Fc and SNA was unique to each blood type (P < .001 and P < .003, respectively). (B) No significant difference was observed in 1918SC hemagglutinin binding to the 3 blood groups (P ≫ .1). (D) Enzymatic treatment of type A and B RBCs with A- and B-Zyme, respectively, significantly decreased SNA density (P < .002). No significant difference was found between B-Zyme–treated and type O RBCs (P = .71). The experiment was repeated 3 times, and representative results for a single volunteer from each blood group are shown. Statistical significance was determined by an unpaired, 2-tailed t test. n = number of cells in each group.