Comparison of human antibody binding to human, porcine, or chimpanzee cells. PBMC isolated from humans, chimpanzees, and GGTA1/CMAH KO pigs incubated with 25% serum collected from five humans. Levels of IgM or IgG binding were detected using fluorescently labeled anti-human IgM or IgG antibodies followed by flow cytometric analysis. Histogram profiles of human IgM and IgG antibody binding are shown for 3 humans (filled gray), 3 chimpanzees (black) and 3 GGTA1/CMAH KO pigs (red). Histogram profiles of PBMC incubated with fluorescently labeled anti-human IgM or IgG antibodies in the absence of human serum are shown to indicate background fluorescence (2° only).