What are the criteria for choosing primary and secondary antibodies in western blotting?

Choosing appropriate primary and secondary antibodies for western blotting is much like choosing antibodies for other types of assays—the primary antibody should be specific to the protein of interest and should be of a different host species than the sample, while the secondary antibody should be reactive against the host of the primary antibody. In addition, the primary antibody should be validated for use in western blotting, and should be specific for either the denatured or native conformation of the protein of interest, depending on the type of PAGE (SDS or native) performed.