Immunocytochemical localization of MG1 mucin in human bulbourethral glands

Salivary mucins MG1 and MG2 have been found in the oral cavity where they perform several functions such as the formation of the mucous layer covering the oral mucosa and teeth. Recent studies have demonstrated their presence in other organs and tissues. The aim of this study was to determine their expression in human bulbourethral (Cowper's) glands. Normal bulbourethral glands were obtained at surgery and fixed in a mixture of 1% paraformaldehyde-1.25% glutaraldehyde in 0.1 m cacodylate buffer and embedded in Epon 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 were intensely reactive with anti-MG1, whereas no labeling was detected for MG2. These results indicate that MG1 is not exclusively a salivary component and furthermore show that bulbourethral glands represent a significant source of the MG1 detected in human seminal plasma.