Age-related changes in the immunoreactivity of the monocyte/macrophage system in rat molar pulp

Defence reactions of the dental pulp potentially involve a variety of immunocompetent cells, particularly class II major histocompatibility complex (MHC)-expressing cells and macrophages. In order to examine how the immunodefence potential of the pulp changes as a function of age, phenotypic distribution of pulpal cells expressing immunoreactivity to monoclonal antibody ED1 (reactive with nearly all macrophages and dendritic cells) was examined immunohistochemically in the lower first molars of developing (new-born to 10-week-old), adult (14-24-week-old) and aged (1-1.5-yr-old) Wistar rats. During tooth development, increasing numbers of ED1+ cells in the pulp also expressed immunoreactivity to ED2 (reactive with a differentiation-related antigen present on resident macrophages). ED1+ and ED2+ cells were distributed throughout the pulp before the tooth formation was completed. OX6+ (class II MHC-expressing) cells started to increase in number shortly after the eruption of the tooth and the increase continued even after the tooth formation had been completed. In aged rats, the density of the pulpal ED1+ cells was maintained at a relatively high level, whereas a significant decrease in the density of OX6+ cells was observed. These results indicate that the density and composition of pulpal cells expressing macrophage-associated antigens vary with increasing age, which most probably is related to changes in the immunological defence potential of the pulp against infection.