Neutral mucins are negative with which stains?

• A. Alcian blue
• B. Colloidal iron
• C. Mucicarmine
• D. Alcian blue, colloidal iron, and mucicarmine

Answer: (D)

Neutral mucins lack the acidic groups (carboxyl and sulfate) that these stains target, so they don’t bind them. Alcian blue at pH 2.5 stains acidic mucins blue, leaving neutral mucins unstained. Colloidal iron detects acidic mucopolysaccharides, so neutral mucins also remain negative with this method. Mucicarmine highlights mucins, but its affinity is strongest for acidic mucins in tissue; neutral mucins do not take up the stain appreciably. To visualize neutral mucins, use PAS, which stains neutral mucins magenta, or combine PAS with Alcian blue to differentiate between mucin types.