The two immunoreactive cells are often close to or in contact with each other (B). the immunocompetent cells in a rat periodontium, indicating a functional interrelationship. It is possible that in a noninflammatory periodontium, the epithelial cells take action not independently, Deltasonamide 2 (TFA) but through conversation with immunocompetent cells. (J Histochem Cytochem 57:315C325, 2009) strong class=”kwd-title” Keywords: epithelial cells, immunocompetent cells, conversation, periodontium, immunohistochemistry Epithelial cell rests of Malassez (ERM) derive from Hertwig’s root sheath, which is a double-layer structure made of epithelial cells that is present round the tooth root. In the periodontal ligament (PDL) of mature teeth, the epithelial cells form strands close to and along the cementum (Diekwisch 2001; Rincon et al. 2006). In addition to epithelial cells, this area also houses several mesenchymal cells, such as cementoblasts and fibroblasts. The presence of abundant keratin filaments in the epithelial cell cytoplasm differentiates these cells from periodontal fibroblasts and cementoblasts (Gao et al. Deltasonamide 2 (TFA) 1988; Peters et al. 1995; Sculean et al. 2001). Therefore, cytokeratin (CK) immunohistochemistry has been used to demonstrate and identify the epithelial cells in the PDL (Kaneko et al. 1999; Fong and Hammarstr?m 2000; Kat et al. 2003). The distribution of the epithelial cell clusters in rat periodontium is usually well documented (Wentz et al. 1950), but the total distribution of the CK-immunopositive cells has not yet been fully characterized. Epithelial cells in the PDL are well known to be the main components of cysts and odontogenic tumors in the pathological state (Ten Cate 1972; Hamamoto et al. 1998; Rincon et al. 2006). In the normal PDL, however, ERM have been Deltasonamide 2 (TFA) regarded as a group of epithelial cells with low or no activity. It has recently been reported that ERM express hard-tissueCrelated proteins such as enamel and bone morphogenetic proteins during cementum repair (Hasegawa et al. 2003). It has also been exhibited that periodontal nerve endings and ERM have a close relationship (Lambrichts et al. 1993; Kvinnsland et al. 2000; Tadokoro et al. 2002,2003) and that an conversation between PDL-derived epithelial cells and fibroblasts regulates the expression of alkaline phosphatase, osteocalcin, and bone sialoprotein (Shimonishi et al. 2005,2008). These reports suggest that ERM function not independently, but through conversation with other cells or in response to extrinsic stimuli. Many bone marrowCderived, immunocompetent cells are known to be widely present in the PDL even under non-inflammatory, physiological conditions (Kawahara and Takano 1995; Vandevska-Radunovic et al. 1997). The presence of an intercellular relationship between epithelial cells and cells expressing class II molecules (OX6+ cells) has been verified (Tadokoro et al. 2008). The diversity of the ultrastructure of these immunopositive cells indicates possible involvement of several types of immunocompetent cells (Tadokoro et al. 2008). There are several immunohistochemical markers for the detection of immunocompetent cells. Cells immunoreactive to ED1, a general macrophage marker, are well known to be broadly distributed in the PDL (Kawahara and Takano 1995; Kan et al. 2001; Kaneko et al. 2008). ED1 antigen is usually localized around the membranes of the phagolysosomal apparatus of nearly all macrophages, and the expression correlates with their phagocytotic capacity (Dijkstra and Damoiseaux 1993; Damoiseaux et al. 1994). However, Deltasonamide 2 (TFA) the relationship between OX6+ and ED1+ cells to epithelial cells in the PDL remains unclear. Therefore, the aim of the present study was to investigate the total distribution and the relationship of epithelial cells immunoreactive to CK and the cells immunoreactive to ED1 and OX6 antibody in maxillary rat molars, by using double fluorescence immunohistochemistry and confocal laser microscopy, as well as transmission electron microscopy. Materials and Methods Animals Fourteen 6-week-old, male rats (Wistar strain), 150 g in excess weight, were used in this study. The rats were housed in polycarbonate cages in a specific pathogen-free environment. The Institutional Committee for Ethics and Animal Use and Care of Matsumoto Dental care University approved all protocols for the animal experiments. Rats were fixed in 4% paraformaldehyde, and the maxillary bone FBL1 containing the teeth was removed, followed by postfixation in the same fixative overnight. The fixed maxillary bone was decalcified in Deltasonamide 2 (TFA) 5% EDTA with 7% sucrose, and.