Individual monoclonal anti-HEL antibodies do not induce antigen loss. C57BL/6 mice were passively immunized with the indicated anti-HEL monoclonal antibodies. Control mice received no antibody. Mice were transfused with a mixture of mHEL RBCs labeled with DiI and C56BL/6 RBC labeled with DiO. Three days after transfusion, peripheral blood was obtained, stained with polyclonal anti-HEL antiserum followed by fluorescently labeled anti-mouse IgG, and anti-HEL staining was measured by flow cytometry. This experiment was reproduced 3 times with similar results. Representative flow plots and histograms are shown.