Direct comparison of the sensitivity of enzyme histochemical and immunohistochemical methods: cathepsin B expression in human colorectal mucosa

Immunohistochemical localization of the proteinase cathepsin B has been com pared directly with localization of cathepsin B activity with a catalytic ( enzyme) histochemical method. The 2 approaches demonstrate principally diff erent aspects of an enzyme. The immunohistochemical method localizes the en zyme protein whether it is active or not whereas the catalytic method visua lizes the functionally active enzyme only. Sensitivity of both approaches t o localize low amounts of enzyme protein or activity has never been compare d. Tn the present study, we show that cathepsin B protein has a wider distr ibution pattern than cathepsin B activity in human colorectal mucosa, which means that inactive cathepsin B protein is present. With respect to sensit ivity of the methods, it is shown that cathepsin B protein could only be de monstrated properly when strong signal amplification was applied by using N anogold with silver enhancement, whereas activity could be demonstrated wit h a simple and direct fluorogenic histochemical assay. It is concluded that catalytic histochemical methods are relatively simple methods for the loca lization of activity of enzymes in tissues and cells and that their sensiti vity is high in comparison with immunohistochemical methods.