Chapter 1 Applications of pathology /Fig 1.04.jpg

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The principles of immunohistochemistry. The aim of the technique is to identify any cell bearing a specific antigen. The cell in the centre has antigens on its surface which are recognized by antibodies, often raised in mice, directed against that antigen. These are the primary antibodies. To demonstrate where these antibodies have bound, a secondary antibody is applied to the section. This antibody is raised in another species, e.g. rabbit, and directed against the Fc component of the primary antibody and therefore binds to it. An enzyme or fluorescent label is bound to the secondary antibody so that a coloured signal is produced. The cells on the left and right bear different surface antigens which are not recognized by the primary antibody and so no signal is produced in relation to them.