Suppression of mitogen-induced proliferation of human peripheral blood lymphocytes by plant lignans

The effects of seven lignans and two neolignans derived from plants and herbs on the concanavalin A-induced proliferation of human peripheral blood lymphocytes in vitro were studied. All compounds showed inhibitory activity with an IC50, ranging from 0.02 to 4.30 micrograms/ml (1.6 x 10(-8) to 1.6 x 10(-5) M). Machilin A (2,3-dimethyl-1,4-dipiperonylbutane), a Lauraceae lignan, was the strongest inhibitor and was quite effective as the synthetic immunosuppressive glucocorticoid prednisolone. The viability of lymphocytes before and after treatment, as assessed by a dye exclusion test, indicated no change, and thus the lignans are not lymphocytotoxic but may inhibit DNA synthesis. The results suggest the value of further assessment of plant lignans as immunosuppressive agents.