The effects of an alcoholic extract (EtOH/H2O, 1:1 v/v) of Dendrostellera (Thymelaeceae) and one of its purified component (MW=663) was evaluated on the growth behavior of two human leukemia cell lines (CCRF-CEM and K562) in the presence and absence of isolated human monocytes. A 50% growth inhibition was observed in both cell lines using 160 ?L of the 1:100 dilution of the crude extract (containing 0.5 g plant powder per mili-liter) or 1.4?M of the purified component. In the co-culture of the isolated human monocytes and each of the leukemia cell lines, however, a four fold of increase in growth inhibition was observed, possibly due to the secretion of TNF-? by the cultured monocytes, under the effect of D.lessertii. The plant extract or its purified component were not only capable of enhancing TNF-? secretion but also they were capable of quenching the number of TNF-? receptors in the cultured monocytes, in less than two hours, in a dose dependent manner. These data, with similarity to Taxol effects on human monocytes and macrophages, may suggest a similar mechanism, down regulation of TNF-? receptors, for the Dendrostellera extract and its purified component.
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