KEL RBC transfusions induce boostable anti-KEL alloantibodies, which result in adverse pregnancy outcomes. (A) Control animals were transfused 3 times with KEL RBCs, with anti-KEL IgG subtypes and IgM measured in pooled serum and compared with pooled serum from 12 females alloimmunized through pregnancy. (B) Anti-KEL IgG measured in transfusion recipients 2 weeks after each transfusion. (C) Naïve or transfused females were bred to KEL males, with total pups born enumerated. (D) percentage of pups alive at weaning evaluated, and (E) percentage of KEL-positive pups determined. (B) Results are representative of 3 independent experiments. (C-E) Results are a compilation of 37 pregnancies. *P < .05.