DEVELOPMENT, SIGNIFICANCE, AND HETEROGENEITY OF MAST-CELLS WITH PARTICULAR REGARD TO THE MAST CELL-SPECIFIC PROTEASES CHYMASE AND TRYPTASE

Mast cells are one of the major effector cells in the pathogenesis of the immediate-type hypersensitivity reaction in a number of non-allerg ic immune disorders as web as in normal physiological processes, In ad dition, it has been shown recently that mast cells also play a signifi cant role in a hfe-saving host response to bacterial reactions. But as much as the immunopathological role of mast cells has been acknowledg ed, these cells have also aroused much controversy and confusion, By n ow it is clear that one explanation for the sometimes even contradicto ry opinions on mast cell function arise from mast cell heterogeneity, This heterogeneity can express itself as differences in histochemical, biochemical, and functional characteristics, Ttl vitro systems provid ed a powerful tool for the investigation of the basic mechanisms for m ast cell development and differentiation and helped to demonstrate tha t mast cell heterogeneity can be traced back to certain cytokine patte rns that are present in different microenvironments. In this context i t has also been shown that the growth factors required for human mast cell differentiation are somewhat different than those for rodents, Tn rodents, the atypical, T cell-dependent mucosal type mast cell can be distinguished from the T cell-independent connective tissue-type mast cell, Tn humans, the strict classification into mucosal and connectiv e tissue-type mast cells is not possible and the content of mast cell- specific proteases chymase and tryptase is the main criterion for mast cell subtypes in humans, The large quantities of tryptase and chymase that are synthesized by mast cells suggest and emphasize the signific ance of these proteinases in mast cell function and stimulated investi gations about the biological properties of these mast cell-specific pr oteases, Comparing their biological activities it becomes clear that t hey share some activities, On the other hand, tryptase seems to partic ipate in proinflammatory mast cell function, whereas chymase seems to be more involved in inflammatory reactions, This review provides a sho rt overview of the discovery, origin, development, and biological sign ificance of mast cells and will then concentrate on mast cell heteroge neity in rodents and humans with respect to the mast cell proteases tr yptase and chymase and their function.