In fluorescence immunohistochemistry, which component is attached to the antibody to enable detection?

• A. A fluorochrome attached to the antibody
• B. An enzyme label attached to the antibody
• C. A colorless dye attached to the antibody
• D. A radioactive tracer attached to the antibody

Answer: (A)

Fluorescence immunohistochemistry detects the target by tagging the antibody with a fluorochrome. When the labeled antibody binds its antigen in the tissue, exposure to specific light excites the fluorochrome, which then emits light that can be seen with a fluorescence microscope. This allows visualization of the antigen’s location and, if multiple fluorochromes are used, even multiple targets simultaneously. Enzyme labels produce colorimetric signals, not fluorescence; a colorless dye wouldn’t emit detectable light; and a radioactive tracer requires autoradiography, not standard fluorescent detection.