Obviously, crude plant extracts from mistletoe contain several distinct components with different biological properties. Interactions of compounds from Viscum album are not well described at present (see Stein and Schietzel, this book). Fischer et al. (1996b) reported an inhibition of ML-cytotoxicity by the vesicles from Viscum album. Furthermore, a synergistic effect was suggested with a mixture of ML and vesicles more effectively increasing uptake of [3H]-thymidine in the DNA of lymphocytes from VA-E-sensitised patients compared to ML and vesicles alone (Fischer, 1997a, b). This effect was suggested to be due to a binding of ML to glycolipids of the chloroplast membranes that form the vesicles. The responding cells were CD4+ T helper cells, but not CD8+ T suppressor/cytotoxic cells (Fischer, 1997a, b).
Preliminary results indicate that the polysaccharides from mistletoe berries induced IL-6 and IFN-y and proliferation of CD4+ T helper cells (Stein et al., 1999c). Simultaneous addition of ML I or ML III with the polysaccharides may enhance the uptake of the thymidine-analogue BrdU in the DNA of cells as compared to the polysaccharides or ML alone. However, these responses showed strong interindividual differences, as some persons responded with enhanced proliferation, while others showed a suppression of polysaccharide-induced BrdU uptake by the ML, and others did not respond at all.
These results indicate that the immune sytem may respond individually towards distinct stimuli. Although not fully understood, several compounds in Viscum album may interact to impact the biological properties of the drug. But this question has to be addressed in further studies.
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