Systemic Mastocytosis

Abstract

Mastocytosis is the condition of unknown etiology characterized by an abnormal accumulation of mast cells occurring in various tissue sites. Mast cells are normally located throughout the body in loose connective tissue with particularly high numbers found in the lungs, skin and gastrointestinal tract. In the lungs, mast cells are associated with large blood vessels and are located in the submucosa of the bronchi and bronchioles (10). In contrast, mast cells in the skin are associated with small blood vessels and also in close proximity to glandular ducts and nerves (28, 58). Mast cells in the gastrointestinal tract occur generally throughout the lamina propria in a random pattern (61). Other sites where mast cells and mast cell precursors are noted in high numbers are in the peritoneal cavity, the thymic capsule and in lymph nodes (50). The origin of mast cells is unclear. Although their presence in the connective tissue has suggested a relationship to fibroblasts, some experiments have suggested their derivation from T lymphocytes (33, 34, 45). These findings are not supported, however, by the presence of typical numbers of mast cells in athymic mice (nu/nu strain) which lack T lymphocytes (49). Other investigators have shown by bone marrow transplantation studies using Chediak-Higashi syndrome mice which have distinctive giant granules that mast cells can be derived from a marrow stem cell precursor (51). The relationship of mast cells to the bone marrow-derived and peripherally circulating basophilic leukocyte is also unknown. Both mast cells and basophils have Fc receptors for IgE on their surface (5, 57) and their granules contain histamine and stain metachromatically when treated with certain dyes such as toluidine blue. Mast cells are characterized by their content of large membrane-bound granules which contain a variety of chemical agents (eg histamine, heparin) which are important mediators of the immediate hypersensitivity reaction.