Immunoelectron microscopic analysis of CD11c-positive dendritic cells in the periapical region of the periodontal ligament of rat molars.

To increase understanding of structural and phenotypic characteristics of dendritic cells (DCs) in the periapical region of the periodontal ligament (PDL) of rat molars, we performed immunoelectron microscopy for CD11c, a previously untested DC marker. Results demonstrated that CD11c clearly recognized DCs, although it also labeled certain macrophage subpopulation(s). In the normal PDL, resident DCs that extended several long cytoplasmic processes from their oval to slender cell body were identified. When the PDL was bacterially challenged by three days of unsealed pulp exposure, relatively small, irregularly shaped DCs with many thin and short cytoplasmic processes, most likely representing newly recruited DCs, were detected. The ratio of DCs in CD11c+ cells was significantly higher than that in ED1 (anti-macrophages and DCs)-positive and OX6 (anti-major histocompatibility complex class II molecules)-positive cells in normal and challenged PDL.