Signal Amplification in Immunohistochemistry at the Light Microscopic Level Using Biotinylated Tyramide and NanogoldSilver StainingAngela Köhlera, Bjarne Lauritzena, and Cornelis J.F. Van Noordenba Department of Ecophysiology and Toxicology, Biologische Anstalt Helgoland in the Alfred Wegener Institute, Hamburg, Germany b Academic Medical Center, University of Amsterdam, Department of Cell Biology and Histology, Amsterdam, The Netherlands Correspondence to: Cornelis J.F. Van Noorden, Dept. of Cell Biology and Histology, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands. E-mail: c.j.vannoorden@amc.uva.nl Signal amplification techniques greatly enhance the sensitivity of immunohistochemical (IHC) and in situ hybridization (ISH) methods. In particular, catalyzed signal amplification (CSA) using labeled tyramide or Nanogoldsilver staining is an important signal amplification tool. We have applied a combination of both techniques, as has been introduced for ISH, for a further increase in sensitivity of an IHC method to detect cathepsin B. This lysosomal proteinase can also be expressed extracellularly, particularly in relation to cancer metastasis. Higher sensitivity of the IHC method was needed because existing methods failed to demonstrate cathepsin B protein where cathepsin B activity was found with a fluorescence enzyme histochemical method. Combined CSA and Nanogoldsilver staining provided the sensitivity that was required. Moreover, this signal amplification method enabled the use of a 10-fold lower concentration of primary antibody (1 µg/ml). Nonspecific background staining was low provided that endogenous biotin, avidin, and peroxidase were completely blocked. The method was reproducible when all steps, and particularly the silver enhancement step, were rigidly controlled. The method resulted in localization patterns of cathepsin B protein that were in agreement with those of cathepsin B activity in serial sections of rat liver containing colon cancer metastases. We concluded that combined application of CSA and Nanogoldsilver staining provides high sensitivity for immunohistochemical methods and that activity localization by an enzyme histochemical method is a very attractive alternative to IHC localization of an enzyme because it is at least as sensitive, it is rapid and simple, and it provides direct information on the function of an enzyme. (J Histochem Cytochem 48:933941, 2000) Key Words: tyramide, signal amplification, Nanogold, immunohistochemistry, enzyme histochemistry, proteinase, cathepsin B, colon cancer metastasis, liver, posttranslational processing
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