Anti-GFP antibody does not mediate enhancement of anti-HOD antibody formation. (A) Flow cytometric analysis of B6 RBCs, GFP RBCs, HOD × GFP RBCs, and B6 RBCs chemically coupled with recombinant GFP after staining with serum from GFP primed recipients. (B) Experimental schematic of passive immunization and evaluation of antibody deposition, antigen levels, RBC clearance, and alloimmunization. (C) Percent survival of HOD × GFP RBCs after transfusion into nonimmunized controls or into recipients who were passively immunized with anti-GFP antibodies or anti-Duffy. (D-F) Assessment of IgG antibody binding (D), detection of RBC surface HOD (E), or detection of RBC surface Ter119 (F) one hour after transfusion of HOD × GFP RBCs into nonimmunized, anti-GFP antibody, or anti-Duffy immunized recipients. (G) Anti-HOD IgG detected at 14, 21, or 28 days after transfusion into nonimmunized passively immunized recipient as indicated. Error bars represent mean ± SD. ∗∗∗∗ P ≤ .0001. ns, not significant.