Mast cell (lung, golden hamster)

Electron microscopy. Mucosa mast cells (mastocytes) are frequently found perivascularly or perineurally. The mast cell shows long thin microvilli at the surface and the cytoplasm is stuffed with granules (1) varying in shape and size. At (2) a Golgi area and at (3) small mitochondria and some electron-dense lysosomes. The larger membrane-bound vesicles (so-called compound granules) show a metachromatic reaction in light microscopy and ultrastructurally a granule exhibits a heterogeneous content (different with species) e.g., osmiophilic granular, filamentous, whorl-like substances. The younger granules are less dense and show a more loosened reticular internal structure. The granules contain among others heparin, histamine, enzymes such as superoxide dismutase, beta-hexosaminidase, tryptase, factors such as neutrophil- and eosinophil-chemotactic factors, vasoactive mediators.