University of Virginia Health System

Mast cell

(a) Normal mast cell- Bone marrow aspirate smear, Wright-Giemsa stain, 1000x

(b) Spindle-shaped mast cell- Bone marrow aspirate smear, Wright-Giemsa stain, 1000x

Description:

Mast cells are tissue-based cells derived from hematopoietic stem cells through the common myeloid progenitor (CMP) and the granulocyte/macrophage progenitor (GMP) pathways. They are not derived from circulating basophils, and rarely ever are seen on a peripheral blood smear from a normal subject. The mast cell precursor cells migrate from the bone marrow through the peripheral blood to tissue and organ sites, and differentiate to mature mast cells. Mast cells are most abundant in the skin, gastrointestinal and genitourinary tracts, and often are located in the perivascular areas, for the most part. The mast cell precursors are not identifiable by light microscopy in the bone marrow or peripheral blood on Wright-Giemsa stained specimens. The morphologic features of a mature mast cell are very distinct. Most are round (a) but some may have an elongated or spindle shape (b). The nucleus is located in the center of the cell and is either round or oval. The cytoplasm is usually packed with coarse, basophilic granules, many of which overlie and partially obscure the nucleus.

Function:

The major function of mast cells is similar to that of basophils, namely participation in the immediate-type hypersensitivity reactions such as asthma, allergic rhinitis and urticaria (hives). They have high-affinity receptors for IgE but differ from basophils in having receptors (c-Kit) for the stem cell factor (SCF, c-Kit ligand). They also participate in the adaptive immune response to parasites through their IgE receptors by binding IgE-coded parasites.

The content of mast cell granules is similar to basophils but differs in having a high content of tryptase, especially in those located in mucosal areas when compared to those that are in connective tissue.

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