The presence of activating FcγRs affects antibody-induced alterations in RBC alloimmunization. (A) Schematic of the experimental design. Anti-Duffy–antibody immunized or nonimmunized B6 or FcγR KO mice were exposed to different doses (10⁷ or 10⁹) of HOD followed by evaluation of anti-HOD antibody formation. (B-C) Anti-HEL IgM (B) and IgG (C) antibody responses were measured in anti-Duffy–immunized or nonimmunized B6 or FcγR KO mice after exposure to 10⁷ and 10⁹ HOD RBCs at various time points, as indicated; n = 5 mice per group. All plots show mean values ± standard deviation. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; and ∗∗∗∗P < .0001. These results are representative of 2 independent experiments.