Immune defense mechanisms of the dentin/pulp complex: Immunohistochemical analysis on the heterogeneity and kinetics of dendritic cells

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This study investigated dendritic cell (DC) subpopulations and co-stimulatory molecule-expressing cells in pulpitis and apical periodontitis by means of immunohistochemistry and transmission electron microscopy.(1) Pulpitis and apical periodontitis were induced in rat molars by making unsealed pulp exposures, and kinetics of DCs was investigated by means of immunoelectron microscopy for MHC class II molecules, CD11c, CD86 and OX62 (a marker for rat DC subpopulation). Results demonstrated that DCs in normal periodontal ligament and periapical lesions consisted of two subpopulations: the subpopulations differently expressed CD11c and OX62 and might differ in lineage, state of maturation and function. In the induced periapical lesions, CD86-expressing cells, comprising approximately 10% of MHC class II molecule-expressing cells, were frequently distributed in the vicinity of nerve fibers, suggesting the involvement of mature DC-nerve interaction in the development of periapical lesions. Moreover, kinetics of DCs during wound healing process of exposed rat molar pulps was investigated after 1VITA-capping, which constantly induced pulp healing with dentin bridge formation. It was demonstrated that DC-like cells showed an accumulation subjacent to the wound surface during initial healing process of the exposed pulps.(2) Immunohistochemistry and electron microscopy for human apical periodontitis revealed that DCs expressing BLA-DR were mainly distributed in lymphocyte-rich areas. By means of laser microdisection and RT-PCR analysis, it was demonstrated that upregulation of CD83 and CD86 on DCs and CD28 on T lymphocytes occurred in the lymphocyte-rich areas. These findings may indicate that DCs act as antigen presenting cells that stimulate T lymphocyte activation.