Mast cell

• Originates from progenitor cells common to basophils, monocytes, neutrophils, and eosinophils
• Their cytoplasm contains granules rich in histamine
• Stains with Leder (chloroacetate esterase), Toluidine blue, Giemsa, and Tryptase
• Their microscopic appearance resembles that of a fried egg
• Note that mast cells reach maturity after migrating into tissues