Electron Microscopic Immunogold Localization of Salivary Mucins MG1 and MG2 in Human Submandibular and Sublingual GlandsMarco Piludua, Sean A. Raymentb, Bing Liub, Gwynneth D. Offnerc,d, Frank G. Oppenheimb,c, Robert F. Troxlerb,c, and Arthur R. Handea Departimento di Citomorfologia, Universita Degli Studi di Cagliari, Cagliari, Italy b Department of Periodontology and Oral Biology, Goldman School of Dental Medicine, Boston University, School of Medicine, Boston, Massachusetts c Departments of Biochemistry, Boston University, School of Medicine, Boston, Massachusetts d Medicine, Boston University, School of Medicine, Boston, Massachusetts e Department of Pediatric Dentistry, School of Dental Medicine, University of Connecticut, Farmington, Connecticut Correspondence to: Arthur R. Hand, Dept. of Pediatric Dentistry, U. of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-1610. E-mail: hand@nso1.uchc.edu The human salivary mucins MG1 and MG2 are well characterized biochemically and functionally. However, there is disagreement regarding their cellular and glandular sources. The aim of this study was to define the localization and distribution of these two mucins in human salivary glands using a postembedding immunogold labeling method. Normal salivary glands obtained at surgery were fixed in 3% paraformaldehyde0.1% glutaraldehyde and embedded in Lowicryl K4M or LR Gold resin. Thin sections were labeled with rabbit antibodies to MG1 or to an N-terminal synthetic peptide of MG2, followed by gold-labeled goat anti-rabbit IgG. The granules of all mucous cells of the submandibular and sublingual glands were intensely reactive with anti-MG1. No reaction was detected in serous cells. With anti-MG2, the granules of both mucous and serous cells showed reactivity. The labeling was variable in both cell types, with mucous cells exhibiting a stronger reaction in some glands and serous cells in others. In serous granules, the electron-lucent regions were more reactive than the dense cores. Intercalated duct cells near the acini displayed both MG1 and MG2 reactivity in their apical granules. In addition, the basal and lateral membranes of intercalated duct cells were labeled with anti-MG2. These results confirm those of earlier studies on MG1 localization in mucous cells and suggest that MG2 is produced by both mucous and serous cells. They also indicate differences in protein expression patterns among salivary serous cells. (J Histochem Cytochem 51:6979, 2003) Key Words: salivary glands, mucous cells, serous cells, intercalated ducts, immunohistochemistry/ postembedding, immunogold labeling
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