Different mast cell mediators produced by different mast cell phenotypes.

The activation of mast cells results in the release of a large variety of inflammatory mediators, many of which are preformed and stored within the secretory granules. Exocytosis of the secretory granule contents releases a macromolecular complex composed of proteoglycan and the neutral proteases. The proteases include both endo- and exopeptidases, suggesting the possibility of a concerted action on unknown substrates. Different proteases are expressed by different mast cells originally defined by histochemical and ultrastructural criteria. From adoptive transfer experiments it appears that the mast cell phenotype is profoundly influenced by the microenvironment. Understanding the development and regulation of the mast cell phenotype is being approached by the development of: (1) An in vitro system of differentiation using in vitro-differentiated mast cells which upon co-culture with fibroblasts demonstrate a phenotypic shift; (2) Kirsten virus-transformed mast cells exhibiting a spectrum of phenotypes. These reagents have allowed the isolation and characterization of the cDNAs of the various preformed protein mediators including the secretory granule proteoglycan peptide core, serine proteases and carboxypeptidase. These cDNAs have provided the first probes for the molecular characterization of the mast cell-associated proteoglycan peptide core, a carboxypeptidase A and a 28,000 Mr serine protease.