Distribution of Immunocompetent Cells in the Oral Mucosae

Objectives: The distribution and morphology of the immunocompetent cells were investigated in the rat oral mucosae, which show regional differences in their structure, by use of immunocytochemistry and histochemistry, focusing on their histological structures. Methods: The palatal mucosa (masticatory mucosa), buccal and sublingual mucosae (lining mucosa) and dorsal surface of tongue (specialized mucosa) were obtained from the mature rats. We used two antibodies to OX6 and ED1, which recognize rat Ia-antigen and macrophage/monocyte lineage, respectively. Ezymatic histochemistry for ACPase and ATPase was also employed to identify macrophages and Langerhans cells, respectively. Furthermore, double staining either with OX6/ED1 or with OX6/ACPase was carried out. Results: Many OX6-immunopositive cells, dendritic- or irregular-shape, were recognized in the lamina propria of oral mucosae: some cells extended their dendritic processes into the epithelial cell layer of the buccal and sublingual mucosae. The epithelial cells with dendritic profiles showed intense ATPase reaction, indicating they were categorized in Langerhans cells. A less number of ED1-positive cells existed in the lamina propria, but never in the epithelial cell layer. Double staining either with OX6/ED1 or OX6/ACPase could divide the immunocompetent cells in the lamina propria into three types; the OX6-positive cells without ED1/ACPase-reaction, the OX6-negative cells with ED1/ACPase-reaction, and the cells co-expressing OX6-ED1/ACPase, each of which possessed characteristic ultrastructual features as demonstrated with immunoelectron microscopy. These cells were regarded as the dendritic-like cells, the macrophage without ability to antigen-presentation, and the macrophage with ability to antigen-presentation, respectively. Conclusion: At least 4 types of the immunocompetent cells exist in the rat oral mucosae. Their region-specific distribution and density suggest the different immune-defense systems in the rat oral mucosae.