Immunohistochemical localization of EpoR in CAM. Immunoperoxidase staining of an 8-day-old chick embryo CAM using polyclonal antibodies to factor VIII (A) and anti-EpoR (B). Note the coexpression of factor VIII and EpoR on vascular endothelial cells. The negative control (preimmune serum replacing the primary antibody) is shown in (C). Bar for (A) through (C) is 5 μm.