PROCEEDINGS |
While the enzymatic procedure alpha d napthol chloroacetate esterase identifies all mast cells (MC) in tissue sections of aldehyde fixed glycolmethacrylate embedded tissue, no histochemical staining procedure does the same. MC in connective tissues stain within five minutes with aqueous toluidine blue, pH 2.5, while intraepithelial, mucosal MC do not. Because cationic dyes alone are commonly used to identify MC, those MC with intraepithelial characteristics evade detection. The difference in staining of the various MC populations is attributed to the heparin matrix of the MC secretory granules in connective tissue versus other sulfated glycosaminoglycans in the granules of intraepithelial MC. We present here a simple modification of the congo red staining procedure developed for eosinophils (Grouls and Helpap, Stain Technol. 56:323, 1981) which will also stain MC granules orange. Thus the application of toluidine blue and separately, congo red, stain 100% of the MC identified by the chloroacetate esterase procedure. The selective staining properties of the mouse MC's are also generally associated with the protease phenotypes of MC established in earlier studiesthe congo red positive intraepithelial MC abundantly expressing mMCP-1 and -2 and the MC in connective tissue generally expressing high levels of the chymases mMCP-4 and -5, the tryptases mMCP-6 and -7, and the exopeptidase, carboxypeptidase-A. This complementary toluidine blue and congo red staining protocol for MC applies over a wide range of normal, transgenic, nematode and bacteria-infected, and knock-out mice examined.