Characterization and localization of T cells in the oral mucosa

Objectives: Periodontal disease (PD) affects the majority of the population and has a negative impact on oral health, dental care costs and has been linked with systemic diseases. PD is the result of a breakdown in the balance between the host response and oral bacteria. For this reason, the mainstay of periodontal treatment - mechanical disruption of the dental plaque biofilm - is only partially successful, as the immune response is not altered. Potential roles for various T helper subsets have been suggested. However, how the phenotype and location of T cells changes throughout disease and contributes to PD pathogenesis remains to be fully elucidated. We sought to determine the phenotype and location of T cells in the oral mucosa in health and periodontal disease.Methods: Mice (n=5/group) were orally infected with Porphyromonas gingivalis or sham-infected with carboxymethyl cellulose and gingival tissue extracted at different times following infection. The extracted tissue was digested to generate a single cell suspension from which T cells were phenotyped by flow cytometry. The location of cells within intact gingival tissue was investigated by whole-mount immunohistochemistry. Gingival tissues were fixed in paraformaldehyde, stained using fluorescently labelled antibodies, then visualised by confocal microscopy.Results: Around 20% of viable CD45+ cells in the gingiva are CD4+ T cells; 4% comprise CD8+ T cells and 0.3% are CD4+CD8+ T cells. The proportions of cells were unchanged following oral infection. T cells and B cells could be visualised in apparently organized aggregates within the intact gingiva in both health and following infection.Conclusions: CD4+ T cells are relatively abundant in the intact oral mucosa. It appears that T cells accumulate around aggregates of B cells, thereby suggesting the presence of lymphoid aggregates in health, however, the role of these remain to be determined.