ABSTRACT
Nearly all antibodies used in immunocytochemistry and related techniques belong to the immunoglobulin G class, the remainder being IgM antibodies. In polyclonal antisera, antibody subpopulations of different specificities and different avidities occur. However, as polyclonal antisera vary so much in their biological properties, it is not possible to define a minimum dilution of them. Antibodies to single amino acids and related molecules may, however, differ in their reactivity with different chemical groups so that a variant of region-specific immunocytochemistry can be executed. Antibodies may therefore be used as either biochemically defined detection reagents in true immunocytochemical techniques or as anatomically defined immunohistological stains. Thus, many antisera contain antigen-antibody complexes, with the antigen component being introduced during the immunization or being of endogenous animal origin. In indirect immunocytochemical methods, which employ labeled antibodies or other labeled proteins as secondary detection reagents, the saturable mechanism could primarily cause unspecificity through binding of the second or third antibody.
