Mast cell polymorphisms. Present concepts, future directions.

Although mast cells are widely distributed in the body, their functions are poorly known. The elucidation of mast cell function is complicated by growing evidence that mast cells are heterogeneous. Recent studies of mast cell ontogeny suggest that microenvironmental stimuli control the phenotypic expression of parts of the genome leading to subtype differences in a common lineage. Mast cells influence cell proliferation, differentiation, and activation in a range of target cells, although until recently they were considered important only in immediate hypersensitivity. However, they function in delayed-type hypersensitivity, potentiate cytotoxicity of eosinophils and macrophages, and are cytotoxic for certain targets themselves. Mast cell mediators influence blood flow and vascular permeability and facilitate angiogenesis. Numerous mast cell mediators are immunoregulatory. In vitro experiments have begun to investigate the role of mast cells in fibrotic diseases. Further knowledge of mast cell heterogeneity will provide the basis for new therapies in inflammatory diseases of the intestine and other organs.