Plasma cells can be demonstrated with which stain?

• A. Methyl Green-Pyronin
• B. Giemsa
• C. Sudan Black
• D. Crystal Violet

Answer: (A)

Plasma cells stand out when there is a stain that highlights their RNA-rich cytoplasm. Methyl Green-Pyronin does exactly this: methyl green binds DNA and stains nuclei green, while pyronin Y binds RNA and stains the cytoplasm pink to red. Because plasma cells produce lots of immunoglobulins, they have abundant rough endoplasmic reticulum and ribosomes, giving the cytoplasm lots of RNA. That makes the cytoplasm appear prominently pink/red, creating a clear contrast with the green-stained nuclei and allowing the characteristic plasmacytic morphology to be seen more easily.

Other stains aren’t as specific for this feature. Giemsa is good for general cellular detail but doesn’t emphasize RNA content in plasma cells the way Methyl Green-Pyronin does. Sudan Black targets lipids, not the RNA-rich cytoplasm, and Crystal Violet is a general dye that doesn’t selectively highlight plasma cells.