Which statement best describes the LSB method?

• A. It uses enzyme-labeled streptavidin to detect bound biotinylated primary antibody on the tissue section
• B. It uses direct enzyme-labeled secondary antibodies
• C. It relies on fluorescent dye-labeled antibodies only
• D. It omits the use of biotin in the detection system

Answer: (A)

LSB hinges on a biotin-streptavidin detection strategy. A primary antibody is biotinylated and binds the target antigen in the tissue. Then an enzyme-labeled streptavidin binds to the biotin on that antibody. The attached enzyme (often HRP or alkaline phosphatase) catalyzes a chromogenic substrate to produce a visible stain. This setup provides signal amplification because streptavidin can bind multiple biotin sites and carry enzyme activity at the binding site, increasing sensitivity compared with direct antibody labeling.

This differs from options that use direct enzyme-labeled secondary antibodies (no biotin involved) or rely solely on fluorescent dyes (which would be a fluorescence-based method, not the chromogenic, enzyme-driven LSB). And it wouldn’t work if biotin were omitted, since biotin is the anchor for streptavidin-enzyme binding.