Toluidine Blue staining is used to demonstrate which cell type?

• A. Mast Cells
• B. Fibroblasts
• C. Adipose cells
• D. Smooth muscle cells

Answer: (A)

Toluidine blue demonstrates mast cells because it is a metachromatic basic dye. Mast cell granules are rich in acidic sulfated glycosaminoglycans (like heparin), which cause a strong metachromatic shift when stained. The granules pick up the dye and change color from the dye’s normal blue to a purple or reddish-purple, making mast cells stand out against the blue-stained tissue background. Other cell types such as fibroblasts, adipose cells, or smooth muscle lack these densely acidic granules, so they do not show metachromasia and appear in the usual blue hue or with background staining instead.