Which stain demonstrates the cytoplasmic granules of mast cells by metachromasia, turning them a reddish-purple colour distinct from the dye itself?

• A Periodic acid Schiff
• B Masson trichrome
• C Toluidine blue ✓
• D Verhoeff van Gieson

Explanation

Mast cell granules contain heparin, a highly sulphated glycosaminoglycan that shifts the absorption spectrum of toluidine blue, giving purple-red metachromatic granules on a blue background. Periodic acid Schiff stains glycogen, mucins and basement membranes magenta but does not show metachromasia. Masson trichrome differentiates collagen from muscle, and Verhoeff van Gieson stains elastic fibres black, so neither targets mast cell heparin. Metachromasia reflects the polyanionic nature of the granule contents.

Reference: Junqueira's Basic Histology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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