A fluid‐phase endocytotic capacity and intracellular degradation of a foreign protein (horseradish peroxidase) by lysosomal cysteine proteinases in the rat junctional epithelium

Abstract

We investigated the co-localization of lysosomal cathepsins B, H and L, and horseradish peroxidase (HRP) in junctional epithelial (JE) cells both as a fluid-phase endocytotic marker to demonstrate the fluid-phase endocytotic capacity of JE cells, and to understand the morphological relationships of the endocytosed foreign substances to lysosomal cathepsins in these cells. The diaminobenzidine (DAB) histochemical and cytochemical methods and immunohistochemical avidin-biotin-peroxidase complex and immunocytochemical post-embedding colloidal gold methods were used. Under light microscopy, DAB reaction products based on HRP were found in JE but were rare or absent in the oral sulcular epithelium and oral epithelium. Immunolabeling for cathepsins B and H was found in the granular structures of the cells, but no cathepsin L was identified. With electron microscopy, DAB reaction products, which indicated both HRP and the azurophil granules of neutrophils, were endocytosed into JE cells. Using a post-embedding technique, gold particles indicating HRP were present on the plasma membrane of JE cells, at the periphery of electronlucent vacuoles, and in the electrondense granules. Gold particles indicating cathepsin B or H were found in the electrondense granules. With different sizes of colloidal golds, the co-localization of cathepsin B or H with HRP was indicated only in the electrondense portion of the larger vacuoles consisting of electronlucent and -dense parts. This study provided the first morphological data which indicate that JE has a fluid phase endocytotic capacity, and which suggest that the lysosomal cathepsins B and H are involved in the intracellular degradation of foreign substances invading through the gingival sulcus in JE cells.

Biological Sealing and Defense Mechanisms in Peri-Implant Mucosa of Dental Implants

“…These ultrastructural characteristics support the idea that the PIE acts as a pathway not only for foreign molecules penetrating into the sub-epithelial connective tissue of the peri-implant mucosa (Ikeda et al, 2002), but also for the flow of peri-implant cervicular fluid from the sup-epithelial tissue (Eley et al, 1991). Both inward (McDougall, 1971;Romanowsky et al, 1988;Yamaza et al, 1997) and outward (Golub et al, 1976;Tanaka 1984;Tanaka and Sakano, 1987) flow are also recognized in the junctional epithelium. The PIE cells also contain tonofilaments (Figure 5a) that associate with desmosomes and hemidesmosomes (Schroeder, 1986).…”

“…At the natural interface, abundant HRP is stopped at the coronal region of the junctional epithelium and IBL (Yamaza et al, 1997). In contrast, high levels of horseradish peroxidase are widely distributed from the upper to middle regions of the PIE around the dental implants (Ikeda et al, 2002) (Figures 10a, 11a).…”

“…They infiltrate into the PIE (Ikeda et al, 2002), suggesting that they are resident or transient leukocytes in the PIE, as well as in the natural junctional epithelium (Yamaza et al, 1997), and function effectively to prevent peri-implant inflammation/disease by their phagocytotic capacity (Ikeda et al, 2002). Junctional epithelial cells have the ability to endocytose foreign substances (Tanaka et al, 1984;Yamasaki et al, 1985;Ayasaka & Tanaka, 1989;Yamaza et al, 1997).…”

“…Various mechanisms of peripheral host defense have been demonstrated in this epithelium (Schroeder & Listgarten, 1997) (Figure 9): (1) phagocytosis and anti-bacterial activity of neutrophils infiltrating into the junctional epithelium (Yamasaki et al, 1979, Tanaka et al, 1988, (2) outward flow of gingival sulcular fluid through the junctional epithelium (McDougall, 1970;Tanaka, 1984;Tanaka and Sakano, 1987), (3) fast turnover or apoptosis of junctional epithelial cells (Schroeder, 1986, Ekuni et al, 2005, (4) continuous epithelial attachment via the IBL throughout the enamel surface (Squier, 1991;Bartold, et al, 2000), (5) endocytotic capacity of junctional epithelial cells for external pathogens (Yamasaki et al, 1979;Tanaka 1984;Tanaka & Sakano, 1987;Ayasaka et al, 1989, Yamaza et al, 1997, and (6) neurotrophic modulation in the junctional epithelium (Kondo et al, 1995;Tanaka et al, 1996;Kido et al, 1999). Fig.…”

An Experimental Study on the Features of Peri-Implant Epithelium: Immunohistochemical and Electron-Microscopic Observations

“…Ayasaka et al 6) reported that the lysosomal enzymes cathepsins B, D, and H exist locally in the junctional epithelium component cells, and Yamaza et al 41) reported that there is an intracellular resolution in the endosome/ lysosome system in the junctional epithelium. Further, elimination of xenobiotica by neutrophil phagocytosis in the intercellular space seems to supplement the defense of the junctional epithelium.…”