Mast cell ultrastructure and staining in tissue.

Mast cells are bone marrow-derived cells that are widely distributed in the tissue. They are found predominantly in the subepithelial tissue near blood vessels and nerves and usually are sprinkled diffusely without forming clusters. In tissue sections stained with hematoxylin and eosin, normal mast cells usually display a round-to-oval nucleus with clumped chromatin and indistinct or no nucleoli.