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Mucin stains

There are a variety of mucin stains, all attempting to demonstrate one or more types of mucopolysaccharide substances in tissues.

The types of mucopolysaccharides are as follows:

  • Neutral – These can be found in glands of the GI tract and in prostate. They stain with PAS but not with Alcian blue, colloidal iron, mucicarmine, or metachromatic dyes.
  • Acid (simple, or non-sulfated) – Are the typical mucins of epithelial cells containing sialic acid. They stain with PAS, Alcin blue at pH 2.5, colloidal iron, and metachromatic dyes. They resist hyaluronidase digestion.
  • Acid (simple, mesenchymal) – These contain hyaluronic acid and are found in tissue stroma. They do not stain with PAS, but do stain with Alcian blue at pH 2.5, colloidal iron, and metachromatic dyes. They digest with hyaluronic acid. They can be found in sarcomas.
  • Acid (complex, or sulfated, epithelial) – These are found in adenocarcinomas. PAS is usually positive. Alcian blue is positive at pH 1, and colloidal iron, mucicarmine, and metachromatic stains are also positive. They resist digestion with hyaluronidase.
  • Acid (complex, connective tissue) – Found in tissue stroma, cartilage, and bone and include substances such as chondroitin sulfate or keratan sulfate. They are PAS negative but do stain selectively with Alcian blue at pH 0.5.

Common stains for mucin:

  • Colloidal iron (“AMP”) – Iron particles are stabilized in ammonia and glycerin and are attracted to acid mucopolysaccharides. It requires formalin fixation. Phospholipids and free nucleic acids may also stain. The actual blue color comes from a Prussian blue reaction. Tissue can be pre-digested with hyaluronidase to provide more specificity.
  • Alcian blue – The pH of this stain can be adjusted to give more specificity.
  • PAS (peroidic acid-Schiff) – Stains glycogen as well as mucins, but tissue can be pre-digested with diastase to remove glycogen.
  • Mucicarmine – Very specific for epithelial mucins.