Immunoblotting

The western blot (sometimes called the protein immunoblot) is a widely used analytical technique used in molecular biology, immunogenetics and other molecular biology disciplines to detect specific proteins in a sample of tissue homogenate or extract.

Artificial antibodies are created that react with a specific target protein. The sample to be tested is prepared and put together with these antibodies on a membrane – if the specific protein sought for is present, after a gel electrophoresis step this will result in an accordingly stained band on the western blot.

Other related techniques include dot blot analysis, and where antibodies are used to detect proteins in tissues and cells by immunostaining, and enzyme-linked immunosorbent assay (ELISA).

The name western blot is a play on the eponymously-named Southern blot, a technique for DNA detection developed earlier by Edwin Southern. Similarly, detection of RNA is termed northern blot and was developed by James Alwine, David Kemp, and George Stark at Stanford. The term "western blot" was given to the technique by W. Neal Burnette, although the method itself originated in the laboratory of Harry Towbin at the Friedrich Miescher Institute.

The confirmatory HIV test employs a western blot to detect anti-HIV antibody in a human serum sample. Proteins from known HIV-infected cells are separated and blotted on a membrane as above. Then, the serum to be tested is applied in the primary antibody incubation step; free antibody is washed away, and a secondary anti-human antibody linked to an enzyme signal is added. The stained bands then indicate the proteins to which the patient's serum contains antibody.

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