ABSTRACT
Protein A-gold (PAG) complex techniques were originally used for postembedding immunoelectron microscopy,17 as was the immunoglobulin G (IgG)-gold complex (IgG-gold) method, also referred to as immunogold staining (IGS).2 PAG is a complex of colloidal gold particles and protein A, a protein that is isolated from the cell wall of Staphylococcus aureus. Since protein A binds to the Fc fragment of IgG among different animal species, such as human, rabbit, guinea pig, mouse, horse, bovine, and others,3,11 PAG has proven useful as a secondary immunoreagent in immunohistochemistry (IHC) and immunocytochemistry (ICC). The preparation of PAG has been described in detail by Roth,20 and PAG labeled with various sizes of gold particles is commercially available.
