Mast cells in peripheral blood smear (human)

Stain: May-Grnwald-Giemsa (MGG). Mast cells (1) from two different smears. (2) Monocyte. Mast cells or tissue basophils are normally present in small numbers in bone marrow smears. They must not be confused with developing basophils. Mast cells are large cells (20-30 m in diameter) with an irregular outline. The cytoplasm is packed with dark-purple stained granules (marked metachromatic in toluidine blue staining) which do not obscure the centrally located, small and round nucleus. The granules contain vasoactive amines such as histamines, lipid mediators, cytokines and enzymes, that are involved in vascular leak, bronchoconstriction, intestinal hypermotility, inflammation and tissue damage. The cells contain IgE receptors which trigger the release of granules upon aggregation with allergen.