Abstract
Direct fast scarlet 4BS (DFS) is a commonly used staining reagent for amyloid. It stains amyloid relatively specifically, but we sometimes experience insufficient amyloid staining and undesirable positive staining of collagen fiber. To prevent such inappropriate staining, several methods of adding salt to the DFS reagent had been reported so far. In this study, we focused on the types and combinations of salts added to the DFS reagent. We prepared seven types of DFS reagent using the following salts: sodium chloride, sodium carbonate, sodium sulfate, a combination of two out of these three types of salt. The reagent without salt was used as a control. Then, we serially sectioned a paraffin block of liver tissue obtained from an autopsy case of systemic amyloidosis (type AA). The slides were stained with the seven DFS reagents mentioned above. On each slide, staining of amyloid and collagen fiber was evaluated. In the assessment of staining quality, we adopted not only the conventional visual method, but also the quantification of stained color using the CIE 1976 L*a*b* color difference formula. There was neither visual nor numerical difference in amyloid staining among the different types of added salt. However, staining of collagen fiber was significantly reduced in the reagents with sodium carbonate. These results suggest that the addition of sodium carbonate to the DFS reagent could be valuable in reducing undesirable staining while maintaining favorable amyloid staining.
