Merkel Cells in Malassez Epithelium
Recent findings indicate that Malassez epithelium (ME) consists of a heterogeneous epithelial cell population. The aim of this study was to investigate the identity of these cells using light and electron microscopy, using protein gene product 9.5 (PGP-9.
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Summary Recent findings indicate that Malassez epithelium (ME) consists of a heterogeneous epithelial cell population. The aim of this study was to investigate the identity of these cells using light and electron microscopy, using protein gene product 9.5 (PGP-9.5). Positive PGP-9.5 immunoreactive (IR) products were recognized in the ground substance of the epithelial cells in both human and cat periodontal ligament (PDL). These immunopositive cells in the cat ME shared the ultrastructural features of Merkel cells (MCs). No neural elements were observed in the vicinity of the cat ME. However, a close relationship between PGP-9.5 IR nerves and immunopositive epithelial cells in the human ME was revealed. This ultrastructural evidence demonstrates the existence of non-innervated MCs in cat ME and suggests the existence of innervated MCs in human ME.
Introduction The epithelial cells, known as ME, in the PDL are remnants of Hertwig's epithelial root sheath. They exist as strands close to the cementum surface after tooth eruption (Hamamoto et al. 1989). Morphological studies have shown that ME in humans and rats is composed of light and dark cells (Brice et al. 1991; KaK. I. Baumann et al. (eds.), The Merkel Cell © Springer-Verlag Berlin Heidelberg 2003
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neko et al. 1999), and there are cytoskeletal similarities between the basal junctional epithelium and ME (Peters et al. 1995). These data imply a non-uniform, heterogeneous structure of ME which has been reported. Recent study of cat PDL confirms the cellular diversity of ME. The cat ME has been demonstrated to contain cells immunoreactive to CGRP, VIP and SP (Kvinnsland et al. 2000). Furthermore, a double immunolabelling for PGP-9.5 and cytokeratin (CK) 20 of cells within ME and gingival epithelium gives strong support to the hypothesis that ME also includes Merkel-like cell properties (Tadokoro et al. 2002). The aim of this study was to investigate the ultrastructure of PGP-9.5 immunopositive cells in human and cat ME and gingival epithelium using light and electron microscopy.
Materials and Methods Specimens from teeth and tooth-supporting tissues in human and cat were used in this study. Human PDL tissue including maxillary incisors was fixed in formalin, rinsed in phosphate buffer and decalcified in formic acid. The cats were anaesthetised with s Nembutal and perfused with paraformaldehyde. The jaws were excised, post-fixed and decalcified in EDTA. After demineralisation, the teeth were cut sagittally at 30 /liD. For immunohistochemical purposes, a standard procedure was used. A polyclonal antibody to PGP-9.5 was used and the antigen detection was determined with the ABC method. Final visualisation was performed by DAB, with or without nickel ammonium sulphate. Following confirmation of the DAB reaction, some cat sections were post-fixed in 1% Os04, dehydrated and then embedded in epoxy resin. Ultrathin sections were examined under a transmission electron microscope.
Results The observation demonstrated the presence of PGP-9.5 IR cells an
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