The increasing power of immunohistochemistry and immunocytochemistry.

Since its introduction in the early 1940s, immunostaining technology has developed in a remarkable way, and the applicability of immunohisto/cytochemical probing methods will unquestionably continue to increase in several directions. Immunofluorescence remains the most powerful and reliable immunohistochemical approach for multicolour staining to evaluate co-localization of two or more antigens in an objective manner. Moreover, the fluorescent colour signals exhibit a relatively consistent relationship to the actual antigen concentration in the test preparation and are hence better suited for quantitative computerized image analysis than light-microscopic observations of immunoenzyme staining. On the other hand, immunoenzyme methods are more economical with regard to reagent consumption and are therefore ideal for the use in semiautomatic staining machines. In addition, the superior morphological correlate provided by the latter methods, makes them more attractive and adequate for most purposes in diagnostic pathology laboratories. However, multicolour immunoenzyme staining provides an easily obtainable and reliable result only when the antigens are known a priori to be separately located, both because of technical problems and because imbalanced colour mixing is difficult to evaluate in the light microscope. All these aspects of immunohistochemistry are briefly reviewed in this historical perspective coloured by the author's own experience.