Immunocytochemical localization of a kallikrein-like serine protease (esterase A) in rat salivary glands.

Light and electron microscopic (EM) immunocytochemical methods have been used to localize arginine esterase A, a kinin-generating enzyme immunologically similar to tissue kallikrein, in rat salivary glands. Both polyclonal and monoclonal antibodies to arginine esterase A were used in these studies. By means of a polyclonal antiserum, esterase A was found in granular tubules of submandibular glands and in striated ducts of all three major salivary glands, in a distribution similar to that of tissue kallikrein. With recently developed specific monoclonal antibodies to esterase A, this enzyme was localized in the granules of some (but not all) granular convoluted tubule cells (GCT) and along the basal membranes (but not in apical granules) of striated ducts. By an EM immunoperoxidase method, esterase A was localized subcellularly in granules of some GCT cells and along the basal cell membranes of the tubule and duct system. Thus, this enzyme is found in some sites (GCT granules) shared with tissue kallikrein, but in some unique sites, i.e., basal membranes of striated ducts. The polyclonal antibody used in the present study cross-reacted with tissue kallikrein, but when absorbed with kallikrein, it gave the staining pattern characteristic of monoclonal antibody to esterase A.