Localization and Phenotype of Resident Macrophages in the Dental Pulp during Rat Mandibular First Molar Development

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Many macrophages are recognized in dental pulp. However, their precise functional roles and the origin are not well understood.In this study, we analyzed the characterization and the localization of dental pulp macrophages during tooth development by immunohistochemistry and immunoelectron microscopy. The first mandibular molars at 1 week finished the tooth crown formation and the molars at 6 weeks finished the root formation. In the dental papilla of molars at 1 week, many CD68⁺ cells were detected. Some of CD68⁺ cells were invaded into the odontoblastic layer at the tip of cusp. A few MHC class II⁺cells were localized in the dental papilla. Most of CD68⁺ cells were CD68⁺/MHC class II^- cells. At 6 weeks, many CD68⁺ cells in the crown dental pulp were invaded in odontoblastic layer, while no CD68⁺ cells were detected at the odontoblastic layer in the root pulp.At this stage, most of CD68⁺ cells were CD68⁺/MHC class II⁺cells. These findings indicated the different distribution of dental pulp macrophages in the crown and the root areas, which suggested that the factors for the localization of macrophages might be different in crown and root pulp. Phenotypic changes of macrophages from CD68⁺/MHC class II^- to CD68⁺/MHC class II⁺ suggested the functional maturation of dental pulp macrophages within the tooth development.