Immunocytochemistry is the most diffuse technique to visualize and localize specific biochemical components in cell compartments and tissues. With this method the antigens are tagged by antibodies that can be visualized with appropriate markers attached directly (direct method) or indirectly (indirect method) to them. The colloidal gold marker system (1 ) is the most widespread immunoelectron microscopy label for postembedding immunocytochemistry. Sections of embedded tissue are incubated with a primary antibody against a particular antigen, which is exposed on the surface of the section, and then with a secondary antibody conjugated to colloidal gold particles of a particular size (indirect method). It is possible to enlarge the colloidal gold size with silver enhancement. This technique is ideal for labeling both intracellular and surface antigens and it can be used for multiple labeling experiments and quantitative studies (2 ).
