Measurement of 1E-SU-IgG binding to cells expressing chimeric receptors. CHO cells transduced with retroviral vectors expressing hamster (AAAA, green), human (UUUU, red) or chimeric (AAUA, orange; AAAU, blue) Xpr1 receptor proteins were incubated with (solid lines) or without (dashed lines) purified 1E-SU-IgG, with fluorescent anti-IgG secondary antibody, and were analyzed by flow cytometry. All analyses were performed in the same experiment with the same FACS settings. Each histogram represents ~13,000 live cells (cells that exclude propidium iodide). The experiment was repeated once with similar results.