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Immunoelectron microscopic identification of lysozyme-expressing cells in human labial salivary glands
T Miyazaki1, T Fujiki, Y Inoue
1Department of Oral Histology, Nagasaki University School of Dentistry, Sakamoto, Japan. miyazaki@net.nagasaki-u.ac.jp
Insights
Human labial glands contain lysozyme, a bactericidal enzyme, produced by immature mucous-type cells. These cells, previously unvisualized, should be reclassified as seromucous cells based on ultrastructural and immunogold labeling evidence.
Area of Science:
- Cell Biology
- Histology
- Glandular Secretion
Background:
- Human labial gland secretions contain the bactericidal enzyme lysozyme.
- The presence and origin of serous cells in labial glands remain unclear at the ultrastructural level.
- Previous studies classified labial gland secretory cells as exclusively mucous-type.
Purpose of the Study:
- To identify lysozyme-expressing cells in human labial glands using advanced electron microscopy techniques.
- To elucidate the ultrastructural characteristics and secretory pathways of labial gland cells.
- To re-evaluate the classification of labial gland secretory cells based on lysozyme production.
Main Methods:
- Utilized microwave fixation and Epon-Araldite embedding for optimal ultrastructural preservation and antigenicity.
- Performed post-embedding immunogold labeling to detect lysozyme localization.
- Employed periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) staining for mucus detection.
Main Results:
- Identified two immature mucous-type cells (I, II) and two mature mucous-type cells (I, II) with distinct ultrastructural features.
- Immunogold labeling revealed specific lysozyme presence in immature-type cells, localized to secretory granules, Golgi apparatus, and rough endoplasmic reticulum.
- Mature-type cells and duct cells showed no specific lysozyme labeling, despite mucus reactivity in mature cells.
Conclusions:
- Human labial glands possess immature-type cells that produce lysozyme, challenging the exclusive mucous-type classification.
- These lysozyme-producing immature cells correspond to serous demilune or acinar cells observed at the light-microscopic level.
- The findings indicate that these immature cells should be reclassified as seromucous cells, contributing both mucus and lysozyme to secretions.
Abstract:
Although human labial gland secretions contain serous components such as the bactericidal enzyme, lysozyme, the presence of serous cells in this gland has yet to be clearly visualized under the electron microscope. The present study identifies lysozyme-expressing cells of the labial glands using microwave-fixed, Epon-Araldite-embedded specimens, which showed excellent preservation of both ultrastructural detail and antigenicity for post-embedding immunogold labeling of lysozyme. Ultrastructurally, all of the secretory cells of the glands appeared to be a mucous-type and have a serial maturation relationship, consistent with a previous report by TANDLER et al. (1969a): their secretory granules were electron-lucent and exhibited reactivity for mucus staining by the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) method. We classified them into two immature types (I, II) and two mature types (I, II). Their distinctive features were the following: 1) relatively small (0.5-1 microm) secretory granules and well-developed basal rough endoplasmic reticulum for the immature types; 2) larger (1-2 microm) secretory granules and well-developed Golgi apparatus, which showed intense PA-TCH-SP reactivity in the 2-3 trans-cisterns, for the mature types; 3) few secretory granules in the immature type I; and 4) the darkest appearance for the mature type II. Immunogold labeling with anti-lysozyme showed specific labeling of the two immature-type cells, in which gold particles were found mainly over the secretory granules and Golgi apparatus, and moderately over the rough endoplasmic reticulum. In the secretory granules, the labeling was distributed throughout the contents and was present even if they showed strong PA-TCH-SP reactivity; in the Golgi area, it was seen over the stacked cisternae, trans-Golgi networks, and condensing vacuoles. No specific labeling was seen in the mature-type cells or in the duct cells. These immature- and mature-type cells were almost equivalent to the "serous demilune or acinus" and "mucous tubule" cells, respectively, at the light-microscopic level. These results indicate that the traditional "immature mucous-type cells" of the human labial glands produce lysozyme and should be classified as seromucous cells.