The myeloma cell line U266 was incubated with primary anti-BMP6 antibody and secondary PE-labeled antibody, pre-incubated with BMP6, or pre-incubated with BMP6 plus heparin, respectively. Light grey line: control, black line: BMP6, primary and secondary antibody ± heparin. A strong labeling of U266 was found, whereas binding is reduced by incubation with heparin.