Twenty dentulous subjects undergoing clinical
therapy for severe
periodontitis were used to determine the longitudinal effects of bacterial plaque reduction in vitro lymphocyte transformation. The
therapy consisted of either complete extractions or partial extractions and periodontal surgery combined with rigorous
oral hygiene. Prior to
therapy lymphocytes from these subjects responded significantly to
Streptolysin O (SLO) but were not transformed significantly by solubilized
dental plaque. However, after
therapy lymphocytes from these same subjects responded significantly to both solubilized
dental plaque and SLO. This indicates that the severe
periodontitis patients were specifically unresponsive to solubilized
dental plaque prior to
therapy. The mechanism of the unresponsiveness is not clear, but probably does not involve serum factors because supplementation of the lymphocyte cultures with pooled homologous plasma from individuals with
gingivitis or moderate
periodontitis (instead of the patient's autologous plasma) did not significantly change the mean lymphocyte responses to solubilized
dental plaque. In addition, lymphocytes from eleven long-term (5--18 yr) edentulous subjects, who were free of oral
inflammation, were significantly transformed by solubilized
dental plaque. The latter lymphocyte responses and those of the treated
periodontitis patients could be due either to the presence of low levels of oral bacteria in the
edentulous mouth or to the lymphocyte transformation assay being a measure of previous
antigen sensitization rather than current disease status. In either case, lymphocyte transformation to solubilized
dental plaque is not a useful diagnostic tool in
periodontitis, but should continue to be a valuable research tool for investigating pathological mechanisms in
periodontitis.