Phenytoin potentiates accessory cell dependent DNA-synthesis in human lymphocytes in vitro

The effect of phenytoin and its major metabolite p-HPPH on concanavalin A (ConA) induced DNA-synthesis of human lymphocytes was studied in vitro. In lymphocyte cultures depleted of phagocytizing cells by iron treatment PHT and p-HPPH, in pharmacologic concentrations, caused a depression of the mitogen response measured as uptake of 3H-thymidine. In contrast, the presence of phagocytizing mononuclear cells during ConA-stimulation in the presence of PHT and p-HPPH caused a potentiation of ConA induced DNA-synthesis. These effects of phenytoin on immunocompetent cells may be of significance in the pathogenesis of the PHT-induced gingival overgrowth, since earlier we have reported the presence of large infiltrates of lymphocytes, mainly T-lymphocytes in gingival biopsies from clinically non-inflamed PHT-induced gingival overgrowth.