Which cell type in connective tissue houses metachromatic granules?

• A. Mast cells
• B. Adipocytes
• C. Fibroblasts
• D. Macrophages

Answer: (A)

Metachromasia with basic dyes identifies mast cells. These cells store cytoplasmic granules rich in heparin and other sulfated glycosaminoglycans. When stained with a metachromatic dye like toluidine blue, the high content of these acidic polymers causes the granules to shift color from blue to purple or reddish-purple, making the granules stand out against the surrounding tissue. Adipocytes lack such granules; fibroblasts don’t contain metachromatic granules as part of their normal role (they synthesize extracellular matrix); and macrophages, while rich in lysosomes, do not show the characteristic metachromatic granules of mast cells. Thus, mast cells are the cell type that houses metachromatic granules.