Diaminobenzidine histochemistry in light microscopy

Basically the DAB-technique localizes 3 enzymes, i.e. peroxidase, catalase, and cytochrome oxidase, but also pseudoperoxidatic activity of hemeenzymes (hemoglobin, myoglobin, etc.). Although at the ultrastructural level, i.e. in cytochemistry, the appropriate conditions for specific identification of each of these enzymatic activities have been extensively studied and reported in the literature, the subject remains open to investigation. In light microscopy DAB staining has been less thoroughly studied. Since DAB histochemistry might have practical interest in daily diagnostic pathology, it appeared worthwhile to work out a method convenient for paraffin embedded tissues. The method consisted of a prolonged incubation 48 h) of small tissue blocks, which had been prefixed for 1 h in 4% formaldehyde. Dehydration and rehydration occurred in graded ethanols; counterstain was obtained by toluidine blue. Although further experiments are needed to specify the physico-chemical conditions for the three enzymatic activities, the results are morphologically superior to that of frozen sections.