Evaluation of the immunomodulatory effects of five herbal plants

A group of medicinal plants including, Silybum marianum, Matricaria chamomilla, Calendula officinalis, Cichorium intybus and Dracocephalum kotschyi which grow in Iran, were extracted with ethanol 70% and the mitogenic activity was examined both on human peripheral blood lymphocytes and thymocytes. Effect of these extracts on proliferative responsiveness of human lymphocytes to phytohemagglutinin (PHA) and on the mixed lymphocyte reaction (MLR) was also investigated. The results obtained indicated that none of the extracts had a direct mitogenic effect on human lymphocytes or thymocytes (stimulation index, SI<0.07). Among the plants studied, C. intybus and C. officinalis showed a complete inhibitory effect on the proliferation of lymphocytes in the presence of PHA (SI range 0.01-0.49). A dose dependent inhibitory effect was obtained in the case of D. kotschyi. Extract of M. chamomilla showed almost no stimulatory effect. A significant decrease in proliferation assay due to 0.1-10 microg/ml of S. marianum was observed (SI<0.46, P<0.05). In MLR, a markedly stimulatory effect with some lower concentrations of all the extracts except Dracocephalum was detected. The highest stimulatory effect was due to 100 microg/ml of S. marianum (SI 2.82). Treatment of mixed lymphocytes with 0.1-10 microg/ml of C. officinalis (SI range 1.34-1.80) and 10 microg/ml of M. chamomilla and C. intybus (SI 2.18 and 1.70, respectively) strongly increased the cell proliferation. In conclusion, this in vitro study revealed the capacity of all the extracts except Dracocephalum to enhance the proliferation of lymphocytes after stimulation with the allogenic cells.