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Mast cells: a unique and functional diversity

In this issue ofClinical and Experimental Allergy , Rossiet al. [1] offer a review of the application of mast cell culture systems to our understanding of mast cell biology, and Kobayashi et al. [2] report the identification of IL-13producing mast cells isolated from the human lung. These papers illustrate the diverse nature of mast cells, and serve to remind us that although mast cells are often implicated in allergic diseases, the physiological purpose of these cells is not completely understood. Nonetheless, there may be an absolute requirement for mast cells in mammalian biology. This conclusion is drawn largely from the failure to identify individuals (normal or otherwise) that have a significant generalized deficiency of this cell type. Mast cells, among the haematopoietically derived cells, are unique in the extent of their functional diversity. These cells have a role in tissue homeostasis, and participate in both innate and acquired immunity (Fig. 1). Mast cells reside at specific locations within the microenvironment, often poised strategically in tissues that interface with the external environment, and next to blood vessels and nerves. These cells are capable of reacting both within minutes and over hours, with either local or systemic effects, to a variety of physical, biological, and chemical stimuli. Mast cells also react in a co-ordinated and graded manner which appears to ensure an appropriate response. There is also a more sinister side to these well-engineered residents of the microenvironment in that well-meaning effector mast cell functions may result in allergic inflammation and perhaps contribute to the pathology of autoimmune diseases.