Distinct KEL founders produce RBCs that express distinct levels of the KEL antigen. (A) Representative flow plot and histogram for distinct KEL RBC donor populations, including forward (FSC) and side scatter (SSC) profile gating strategy, staining for the KEL antigen with anti-KEL antibodies, and the level of Ter119 observed in each population. (B) Quantification of FSC profile, KEL antigen levels, and Ter119 staining in KEL^hi, KEL^med, and KEL^lo RBCs. *KEL^lo vs B6, P < .001; **KEL^med vs B6, P < .0001; and KEL^med vs KEL^lo, P < .001; ***KEL^hi vs B6, P < .0001; KEL^hi vs KEL^lo, P < .0001; and KEL^hi vs KEL^med, P < .0001. (C) Titration of anti-KEL polyclonal antibody against KEL^hi, KEL^med, and KEL^lo RBCs followed by flow cytometric examination. (D) Examination of antibody binding to KEL^hi, KEL^med, and KEL^lo RBCs following incubation with serum isolated from recipients that were passively immunized with the indicated doses of anti-KEL antibody. Error bars represent mean ± SEM. n = 3-5 mice per group. Each panel represents data reproduced 3 times.