Dendritic Cells: A Novel Cellular Component of the Rat Incisor Enamel Organ Appearing in the Late Stages of Enamel Maturation

Abstract

Immunocompetent cells in the enamel organ of rat incisors were examined immunohistochemically using OX6, ED1, and ED2 monoclonal antibodies known to recognize the Class II MHC molecules, a monocyte-macrophage lineage, and residential macrophages, respectively. The OX6 immunopositive cells (MHC cells) were located exclusively in the enamel maturation zone. MHC cells increased in number in the incisal direction and occasionally extended cytoplasmic processes deep into the ameloblast layer. Migration of MHC cells in the ameloblast layer were also encountered. MHC cells lacked phagolysosomes and could be distinguished from typical macrophages. ED2 immunopositive cells were not seen in the enamel organ. ED1 positive cells displayed identical localization to MHC cells except that some appeared in the transitional zone. MHC cells could not be seen in the enamel organ of rat molar tooth germs. Our data confirmed the presence of a large population of "dendritic" immunocompetent cells in the enamel organ of rat incisors and characterized the ultrastructural features of these cells. Biological significance of the immunocompetent cells in the enamel organ during amelogenesis needs to be clarified.

Effects of a Macrolide Antibiotic on Enamel Formation in Rat Incisors-Primary Lesion of Ameloblast at the Transition Stage

“…During enamel maturation, a considerable number of ameloblasts are lost, as well as the transition stage [10,18,20]. In the transition stage, about 25% of ameloblasts show degeneration and necrosis and are phagocytosed by intermediate layer cells or macrophages [9,10,18].…”

Presence of Anti-cystatin C–positive Dendritic Cells or Macrophages and Localization of Cysteine Proteases in the Apical Bud of the Enamel Organ in the Rat Incisor

“…Dendritic cells in the enamel organ of the maturation zone of rat incisors are scarce in juvenile animals, whereas numerous dendritic cells are present in the adult animals (Takano et al 1996). This study showed the presence of round cystatin C-positive cells in the incisor apical bud of the newborn rat.…”

“…Because of its bulbous morphology, the proliferation zone has been proposed as the apical bud (Ohshima et al 2003), and this latter terminology is used in this report. In more advanced zones of the enamel organ of rat incisor, that is the transition and maturation zones, many dendritic cells invade the epithelial layer (Nishikawa and Sasaki 1996;Takano et al 1996). In particular, in the late maturation zone, numerous dendritic cells are localized in the epithelial papillary layer (Takano et al 1996).…”

“…Dendritic cells from the transition and maturation zones bind anti-MHC Class II antibodies (OX6) (e.g., antigen-presenting cells) and anti-lysosomal membrane protein antibodies (ED1) (e.g., macrophages and dendritic cells). These dendritic cells, however, do not bind ED2, antibody for resident macrophage protein (Takano et al 1996;Nishikawa and Sasaki 2000).…”

“…In more advanced zones of the enamel organ of rat incisor, that is the transition and maturation zones, many dendritic cells invade the epithelial layer (Nishikawa and Sasaki 1996;Takano et al 1996). In particular, in the late maturation zone, numerous dendritic cells are localized in the epithelial papillary layer (Takano et al 1996). Dendritic cells in the transition zone ingest apoptotic ameloblast fragments and enamel matrix remnants in the papillary layer and thus may function in clearing unnecessary cells and materials and in acquiring immunotolerance Sasaki 1996,1999).…”