Near-complete removal of the KEL glycoprotein antigen on RBCs occurs in wild-type, but not FcγR KO × C3 KO (double-KO), recipients treated with anti-KEL immunoprophylaxis. (A) KEL RBCs labeled with the lipophilic dye DiO were recovered from recipients transfused in the absence or presence of anti-KEL immunoprophylaxis 10 minutes, 1 hour, and 24 hours after transfusion and incubated directly with fluorescently conjugated anti–mouse IgG (P < .05 at 1 hour and 24 hours after transfusion by 2-way ANOVA between double-KO and other recipients treated with immunoprophylaxis). (B) Side-by-side comparison of the KEL antigen detection signal versus the signal of RBCs incubated directly with fluorescently conjugated antibody 24 hours after transfusion, in FcγR × C3 (double-KO) recipients treated with anti-KEL immunoprophylaxis. (C) Western blot data of membrane preps from RBCs recovered from wild-type (B6) or FcγR × C3 (double-KO) mice 24 hours after transfusion, in the absence or presence of treatment with anti-KEL immunoprophylaxis. The data in A and B are representative of 2 to 3 independent experiments with 3 mice per group per experiment; error bars indicate SD. The data in C are representative of 2 independent experiments with 2 mice per group per experiment.