ABSTRACT
Aqueous or ethanol extracts obtained from the leaves of Mikania glomerata (Asteraceae) and different species of Kalanchoe (Crassulaceae) or Alternanthera (Amaranthaceae) and from seeds of Paullinia cupana (Sapindaceae) blocked the capacity of human lymphocytes to proliferate in vitro. In all cases, a proliferative response induced by cocultivation of lymphocytes with phytohemagglutinin was inhibited even after depletion of phagocytic mononuclear cells by adherence. A flavonoid-enriched fraction from K. pinnata and an ethyl acetate fraction from A. tenella were 10 to 20-fold, respectively, more potent in inhibiting lymphocyte proliferation than their original crude extracts. In contrast, these fractions had no inhibitory action on human natural killer activity. Lymphocyte suppression by the extracts was not due to a cytotoxic effect. Pre-incubation with the highest extract concentrations did not affect the capacity of lymphocytes to proliferate, after removal of extracts from the medium. These results indicate a direct action of the extracts on lymphocytes. They also suggest that these medicinal plants may contain potential immunosuppressive substances that selectively act on activation steps of the cells of the immune system.
