Protein A (Staphylococcus aureus) and Protein G (Streptococcus species) are used as general reagents for binding primary antibodies or surface IgG in mammalian tissues. Protein G is recommended for most species, including mouse and rat.
Protein A is recommended for cat and guinea pig. Neither is recommended for detection of IgA or IgM, for detection of Fab fragments, or for detection of avian IgG. When bound to a resin like agarose, Protein A and Protein G may be used to affinity purify immunoglobulins from serum or ascites fluid. Protein L (Peptostreptococcus magnus) has an affinity for Κ light chains from various species and will detect monoclonal or polyclonal IgG, IgA, and IgM as well as Fab, F(ab’)2, recombinant single-chain Fv (scFv) fragments that contain kappa light chains, and chicken IgG. However, Igs from species such as bovine, goat, sheep, and horse contain almost exclusively lambda chains, and will not bind well, if at all, to Protein L. The capacity of these proteins for IgG varies with the species.