Antigen loss occurs in multiple different murine strains. C57BL/6, BALB/c or C3H mice were actively immunized with HEL/CFA. Mice were transfused with a mixture of mHEL RBCs labeled with DiI and C57BL/6 RBCs labeled with DiO. Four days after transfusion, peripheral blood was obtained and stained with polyclonal anti-HEL antiserum followed by fluorescently labeled anti–mouse IgG; anti-HEL staining was measured by flow cytometry. (A-C) Numbers in the upper left and lower right quadrants represent the percentage of circulating transfused B6 or mHEL RBCs, respectively. (D-F) B6 and mHEL histograms are shown individually and then overlaid. This experiment was reproduced 3 times with similar results. Representative flow plots and histograms are shown.