Antibodies are important research tools, diagnostic reagents and therapeutic drugs. As reagents they are used in a variety of different immunoassay formats including western blot, immunohistochemistry (IHC), ELISA, sandwich immunoassay, immunoprecipitation, flow cytometry, and functional assays. The way in which an antibody is made determines the form of antigen it binds, the site of binding, the strength of binding, crossreactivity, and the type of assay in which the antibody will work. Therefore, it is necessary that antibodies be developed and selected in a manner consistent with the intended purpose.