The stimulation of human peripheral blood lymphocytes by solubilized dental plaque: macrophage and T-cell dependence

This study compared the ability of human peripheral blood lymphocyte subpopulations from individuals with moderate periodontitis to proliferate in response to stimulation with solubilized dental plaque, phytohemagglutinin (PHA), pokeweed mitogen (PWM) and purified protein derivative (PPD). Unseparated mononuclear lymphocytes and recombined purified T and B lymphocytes (4/1) responded significantly to all of the stimulants. DNA synthesis in response to solubilized dental plaque was maximal after 6 to 7 days of culture; the optimum dose was usually 10 to 20 micrograms/ml. T lymphocyte subpopulations purified by rosetting with sheep red blood cells and density gradient centrifugation responded well to PHA and PWM, but were unresponsive to solubilized dental plaque and PPD unless supplemented with 2% autologous macrophages, demonstrating that T cell responses to solubilized dental plaque and to PPD are macrophage-dependent. T cell-depleted enriched B lymphocyte subpopulations were poorly responsive to all of the tested stimulants; however, the responses of these cells to solubilized dental plaque and to the known T cell-dependent B cell mitogens PWM and PPD were increased significantly by the presence of 10% mitomycin C-treated T cells, demonstrating that B cell proliferation to solubilized dental plaque is T cell-dependent. Thus, cellular interactions between macrophages, T lymphocytes and B lymphocytes are required to obtain optimal proliferative lymphocyte responses to solubilized dental plaque. Since both T and B lymphocytes respond to dental plaque stimulants, they both have the potential to mediate periodontal inflammation and tissue destruction whenever dental plaque stimulants gain entrance into the periodontal tissues.