Wild-type and hGPA-Tg-mRBCs were incubated with distilled water as a positive control (defined as 100% hemolysis) or with guinea pig serum alone as a negative control (defined as background hemolysis). Test samples contained guinea pig serum as a source of complement and defined concentrations of purified mAbs. Hemolysis was determined by spectrophotometric evaluation of absorbance at 414 nm of the supernatant of each reaction and the results are presented as percent hemolysis compared to the distilled water control. All samples were tested in duplicate and the average results are presented. Binding of the mRBC-specific J11d anti–CD24 IgM mAb led to hemolysis of both types of mRBCs; the E4 anti–hGPA IgM mAb only hemolyzed hGPA-Tg-mRBCs.