Immunostimulation of some Thai medicinal plant extracts

Abstract

Screens for in vitro immunostimulating activity of 15 Thai medicinal plant extracts on rat splenic lymphocyte proliferation and J774A.1 macrophage phagocytosis. The effects of plant extracts on cytokine production were also evaluated. Five crude ethanolic plant extracts were found to stimulate lymphocyte proliferation at the concentration of 12.5 ug/ml. These were the extracts of Harpullia arborea, Limnophila rugosa, Mitrephora maingayi, Pseuduvaria setosa and Stelechocarpus cauliflorus. Furthermore, Harpullia arborea and Pseuduvaria setosa showed phagocytosis enhancement at the same concentration. The ethanolic extract of Limnophila rugosa has not been further purified due to the limitation of the plant material. It demonstrated the highest stimulation activity on rat lymphocyte proliferation without an effect on macrophage phagocytosis. This plant extract also exhibited the highest inducing effect on IL-12 secretion from J774A.1 cells. The other active plant extracts were further submitted to fractionation and purification process to yield the immunostimulant compounds. Kaurenoic acid and [beta]-sitosterol was obtained from the hexane fraction of Mitrephora maingayi and Stelechocarpus cauliflorus, respectively. Both compounds exhibited maximum stimulation effect to rat splenic lymphocytes at the concentration of 41.4 uM (37.7 +-0.9 % stimulation), and 60.4 uM (41.4 +-6.8 % stimulation), respectively. Quebrachitol, isolated from the aqueous fraction of Harpullia arborea showed maximum lymphocyte proliferation stimulation at the concentration of 257.7 uM with 45.7 +-1.5 % stimulation and enhanced the phagocytic activity of J774A.1 cells at the concentration of 515.5 uM (40.1 +-3.6 % phagocytosis). 1,2,3-trimethoxy-4,5-dioxo-6a,7-dehydroaporphine and ouregidione obtained from the chloroform fraction of Pseuduvaria setosa maximum stimulated splenic lymphocyte proliferation at the concentration of 18 uM (78.4 +-5.6 % stimulation) and 37.2 uM (88.1 +-15.2 %stimulation), respectively. In addition, both compounds enhanced the phagocytic activity of J774A.1 cells at the same concentration. The isolated pure compounds, i.e., kaurenoic acid, [beta]-sitosterol, quebrachitol, and ouregidione were capable to enhanced IL-12 secretion from J774A.1 cells, except 1,2,3-trimethoxy-4,5-dioxo-6a,7-dehydroaporphine could not induce the IL-12 production. Among all isolated compounds, only kaurenoic acid could weakly induced the IL-2 production from rat splenic lymphocytes. The results from this work could provide preliminary information on the immunomodulating effect of some Thai medicinal plants, which may be of benefit in increasing the immunity for the treatment of AIDS, infectious disease and cancer.