Flow cytometry analysis of human or baboon IgG/IgM binding to erythrocytes. A 4-fold serial dilution of human or baboon sera was used to label erythrocytes from Dom, GGTA1 KO and GGTA1/CMAH KO pigs, as well as baboons, chimpanzees, and humans. Bound human and baboon antibody was detected with fluorescently conjugated anti-human IgG or IgM antibodies. Erythrocytes from each group were treated with secondary antibody only as a control. Histograms shown are representative of 3 experiments (Panel A). IgG/IgM binding was assessed after normalization with the MFI of erythrocytes incubated with only secondary antibody. The results from individual experiments using 6.3% final sera are expressed as mean ± SEM, n=3 and *p<0.05 (Panel B).