We prepared monoclonal antibodies (McAbs) against secretory granule membrane of the rabbit parotid gland. Two McAbs, IgG2a (McAb-116) and IgM (McAb-64), which were directed to the glycoprotein of 55-60 Kd which contained N-linked carbohydrate, were obtained. It was suggested that this glycoprotein was an integral membrane protein and localized on the luminal side of secretory granules. The following cells were immunostained with the McAbs: a) among exocrine cells, acinar cells of the parotid and submandibular glands, chief cells of the stomach and pancreatic exocrine cells; and b) among endocrine cells, parafollicular cells of the thyroid gland, adenohypophyseal cells, enterochromaffin cells of the digestive tract, adrenal medullary cells and juxtaglomerular cells of the kindney. These findings suggested that secretory granule specific antigen (SGSA), existed commonly in the secretory granules of both exocrine and endocrine cells. Immunoelectoron microscopy revealed that SGSA was localized exclusively along the membranes of secretory granules in the parotid acinar cells, exocrine pancreatic cells and adenohypophyseal cells. In parotid gland, SGSA was also recognized on the membranes of the Golgi lamellae and vacuoles and apical cell membranes. It is suggested that SGSA may play an important role in secretory granule formation and exocytosis in secretory cells. The two McAbs may provide a useful tool for investigating the formation, translocation and recycling of secretary granule membrane proteins.
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