Which of the following are common counterstains used in immunohistochemistry?

• A. Mayer Hematoxylin, Methyl Green, Nuclear Fast Red
• B. Eosin Y, Aniline Blue
• C. Safranin O, Fast Green
• D. Crystal Violet, Carbol Fuchsin

Answer: (A)

In immunohistochemistry, a counterstain provides visible contrast to the chromogenic signal and helps define tissue architecture, especially the nuclei. A good nuclear counterstain is compatible with the chromogen and highlights nuclei without masking the specific stain. Mayer Hematoxylin stains nuclei blue and is a classic choice; Methyl Green offers a green nuclear stain often used in certain IHC protocols; Nuclear Fast Red gives pinkish-red nuclei and can provide strong contrast alongside brown DAB signal. Together, these three are common nuclear counterstains used in IHC to delineate nuclei and overall tissue context.

The other options mix stains that are not standard nuclear counterstains in IHC—such as eosin-like stains that color cytoplasm, or stains used for other histology techniques that don’t provide the same crisp nuclear contrast or compatibility with chromogenic IHC signals.