Immunohistochemistry and Immunocytochemistry

Immunochemistry is the demonstration of a particular antigen (typically a protein) in a histological tissue section (immunohistochemistry, (IHC)) or in a cytological preparation (immunocytochemistry, (ICC)) using an antibody that specifically binds to that antigen. The binding of the antibody is visualized using an appropriate reporter label, which can be either the precipitated end product of an enzyme/substrate reaction or fluorescent. Amplification systems can simply consist of a reporter label directly conjugated to a ‘secondary’ antibody that recognizes and binds to the species and antibody subclass of the primary antibody, through to more complex amplification systems such as the avidin-biotin complex (ABC) or compact polymer, which offer a greater degree of sensitivity. There are four common specimen formats for immunochemistry, namely paraffin embedded, frozen, free floating and cytological. Glutaraldehyde molecules are also relatively small, consisting of two aldehyde groups separated by a flexible chain of three methylene bridges.