Immunostaining is a general term in biochemistry in that applies to any use of an antibody and some colouring agent to detect a specific protein in a sample. The most common applications are after gel electrophoresis or within tissue slices in immunohistochemical staining.

Antibodies that detect the protein of interest are generated by a foreign host species (a polyclonal antibody) or cultured immune cell clones (monoclonal antibodies). After exposure to the foreign protein, the antibodies can be harvested and used as very specific and sensitive detection agents. Antibodies so generated are known as "primary antibodies," as they bind directly to the protein of interest.

Some immunostaining agents can be applied in a single stage, where the primary antibody is directly linked to a colouring agent. Usually this is not the case, and the primary antibody is targeted by a "secondary" antibody, targeting a species-specific part of the structure of the primary antibody.

This alternative is advantageous in many ways. Most importantly, the signal is amplified, as multiple secondary antibodies will bind to a primary antibody. It also allows for a high variety of primary antibodies - researchers can make their own antibodies and not have to conjugate them to a colouring agent themselves. Finally, it means that a variety of colouring agents can be conjugated to any given species of secondary antibody, and are available in ready supply. This has opened the door to "double-labelling" experiments, where several proteins can be co-localised through the use of antibodies for different proteins raised in different species.

See also Western blot and immunohistochemical staining.

Immunology | Protein methods | 免疫染色