What is the primary reason for using the LSB method in immunohistochemistry?

• A. This method uses an enzyme-labeled streptavidin to detect the bound biotinylated primary antibody on the tissue section
• B. It uses direct labeling of the primary antibody with a fluorescent tag
• C. It replaces the ABC method entirely with no signal enhancement
• D. It uses avidin directly conjugated to an enzyme without biotin

Answer: (A)

Signal amplification through the biotin–streptavidin interaction is the key idea behind the LSB method. In this approach, the primary antibody (or its tag) provides biotin, and an enzyme-conjugated streptavidin binds tightly to that biotin, delivering the enzyme to the site of the antigen. The extremely strong biotin–streptavidin bond makes the enzyme signal stronger and more detectable than direct labeling, boosting sensitivity. This is why LSB is used: it enhances signal rather than just labeling the antibody, unlike direct labeling approaches. It’s a different amplification strategy from the ABC method, which uses a biotin–avidin complex with more layers, but the essential point is the same: leveraging the biotin–streptavidin interaction to bring the enzyme to the antigen for a robust chromogenic readout.