Toluidine Blue staining is used to demonstrate which connective tissue cell type?

• A. Fibroblasts
• B. Mesenchymal
• C. Adipose
• D. Mast Cells

Answer: (D)

Toluidine blue demonstrates metachromasia, a color change that identifies certain granule-rich cells in connective tissue. Mast cells contain cytoplasmic granules packed with highly sulfated glycosaminoglycans (such as heparin). When toluidine blue binds to these granules, the color shifts from blue to a purple-reddish hue, making mast cells stand out against the blue background. Other connective tissue cells—fibroblasts, mesenchymal cells, and adipocytes—do not contain these metachromatic granules, so they do not show the distinctive color change.