The cells with the rose-violet cytoplasm shown are most likely which cell type?

• A. Mast cells
• B. Basophils
• C. Langerhans cells
• D. Macrophages

Answer: (A)

Staining reveals granule-rich cells by color, and the key here is metachromasia. Mast cells in connective tissue contain large granules rich in sulfated proteoglycans like heparin. When a metachromatic stain such as toluidine blue is used, these granules shift color from blue to rose-violet. The prominent rose-violet cytoplasm you’re seeing fits a cell loaded with these granules, which is characteristic of mast cells.

Basophils also have granules that stain with basic dyes, but they are circulating leukocytes with dense, dark granules and aren’t typically described as having rose-violet cytoplasm in tissue sections. Langerhans cells are dendritic antigen-presenting cells with pale cytoplasm and do not exhibit metachromatic granules. Macrophages have more diffuse, often foamy or finely vacuolated cytoplasm and lack these dense metachromatic granules.

So the rose-violet staining points to mast cells due to their metachromatic granules responding to the dye.