cyto 5

• Special stains


  Stains designated to distinguish from the routine stain, H&E. Sometimes requested after examining the H&E to demonstrate the presence or lack of a particular feature.
• Mucins


  High molecular weight glycoproteins found dispersed throughout the epithelia of the gastrointestinal, respiratory and reproductive tract. Composed of a central protein core with multiple chains of carbohydrates (polysaccharides) attached.
• Proteoglycans


  Glycoprotein molecules which share structural similarities with mucins, but have a different protein core structure.
• Classification of mucins


  • Charged or "acid" mucins (contain carbohydrates with carboxylate or sulphonate groups)
  • Neutral mucins (lack acidic groups and carry no net charge)
• Periodic Acid Schiff (PAS) stain


  Versatile and widely used technique for demonstrating glycoproteins, carbohydrates and mucins. Recognizes neutral mucins.
• PAS stain principle


  1. Oxidation of 1,2 glycols to form Schiff reactive aldehyde groups

  2. Schiff reagent reacts with aldehyde groups to form bright red magenta end product
• PAS stain


  • Sensitive for detection of neutral mucins and acid mucins with sialic acid
  • Also used for detection of glycogen and glycoproteins
  • Valuable for visualizing basement membranes
• PAS-D stain


  Diastase (α-amylase) depolymerizes glycogen, which is then washed out of the section
• Alcian blue - PAS stain

  Combination used to distinguish neutral mucins (stain magenta with PAS) from acid mucins (stain deep blue with Alcian blue)
• Characteristics of neutral mucins

  • Stain with PAS
  • Do not stain with Alcian blue, colloidal iron, mucicarmine, or metachromatic dyes
• Characteristics of acid (simple, mesenchymal) mucins

  • Contain hyaluronic acid
  • Stain with Alcian blue pH 2.5, colloidal iron, and metachromatic dyes
  • Digest with hyaluronidase
• Characteristics of acid (complex, connective tissue) mucins

  • Found in tissue stroma, cartilage, and bone
  • Include chondroitin sulfate and keratan sulfate
  • PAS negative, stain selectively with Alcian blue pH 0.5
• Characteristics of acid (complex, sulfated, epithelial) mucins

  • Found in adenocarcinomas
  • PAS usually positive
  • Stain with Alcian blue pH 1, colloidal iron, mucicarmine, and metachromatic stains
  • Resist hyaluronidase digestion
• Clinical significance of mucins

  • Increased production in many adenocarcinomas
  • Over-expressed in lung diseases like asthma, bronchitis, or cystic fibrosis
  • Membrane mucins MUC1 and MUC4 have pathological implications
  • Potential as diagnostic markers
• PAS staining can be used to assist in the diagnosis of several medical conditions