The effect of blends of monoclonal HEL-specific antibodies on the AMIS effect. Monoclonal HEL-specific antibodies reactive with different (A-B,E) or blocking epitopes (C-D) were assessed for RBC binding (A,C) and AMIS induction (B,D-E). C57BL/6 (B) or FcRγ^−/− (E) mice were transfused with 10⁷ HOD RBCs in the presence of 0.5 µg of individual monoclonal antibodies that bind to different epitopes on the HEL protein (4B7 and 2F4) or with a blend (0.25 µg of each monoclonal antibody) of 4B7 and 2F4. C57BL/6 mice were transfused with 10⁷ HOD RBCs in the presence of 0.5 µg of individual monoclonal antibodies that block each other’s binding to the HEL protein (5B9, 8E12, or 4B7) or with a blend (0.16 µg of each monoclonal antibody) of 5B9, 8E12, and 4B7 (D). HOD RBCs alone (10⁷ per mouse) and untreated mice (Nil) were used as controls in the AMIS experiments. Mice were bled for serum on day 0 (1 hour after transfusion) and on day 7. IgM antibodies with specificity for HEL were evaluated by ELISA. The binding of the individual monoclonal antibodies or their mixtures with the HOD RBCs was assessed by flow cytometry (A,C). HOD RBCs incubated with secondary antibody only (Control-2nd Ab) were used as negative staining control. Data represent the mean ± SEM of 3 different experiments. MFI, mean fluorescence intensity. *P < .05; **P < .01; ***P < .001; ****P < .0001.