We demonstrated that a common antigen (Golgi-associated antigen, GAA 108) is present in the Golgi apparatus of serous exocrine cells, using an immunohistochemical method with monoclonal antibodies (MAb) 108 (IgG1) and 18 (IgM), raised to the microsomal fractions of rat parotid gland. The MAb reacted with polypeptides of molecular weights in the 58-170 KD range in parotid gland on Western blot analysis. The Golgi apparatus of the following cells was immunostained with these MAb: acinar cells of parotid gland, pancreas, and exorbital lacrimal gland, serous cells of sublingual gland, chief cells of stomach, and epithelial cells of rat prostate. However, positive reaction occurred throughout the entire cytoplasm of submandibular gland acinar cells. Immunoelectron microscopy (IM) revealed antigen (GAA 108) localization in the medial and trans-Golgi cisternae and trans-Golgi network (TGN), including condensing vacuoles, in parotid, exorbital lacrimal, and pancreatic acinar cells, and serous acinar cells of sublingual gland. Lysosomes and apical cell membranes also stained positively in some cells. In the submandibular gland reactions were observed in the medial and trans- Golgi cisternae, condensing vacuoles, secretory granule contents, cell membrane, and in some duct lumens. These results suggest that although GAA 108 is found in the Golgi apparatus of most serous exocrine cells, it is secreted by a regulated pathway in the acinar cells of submandibular gland.
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