Thionins from Viscum album L: Influence of the viscotoxins on the activation of granulocytes

Background: Extracts from European mistletoe (Viscum album L.) are applied in adjuvant cancer treatment, and some components, especially the mistletoe lectins (ML) have been immunologically characterised, but not the thionins , termed viscotoxins (VT). Materials and Methods: The influence of the VT o n human granulocytes was studied by flow cytometry: E.coli co-stimulated re spiratory burst by oxidation of dihydrorhodamine 123 to rhodamine 123 and p hagocytosis by ingestion of FITC-labelled E.coli., Results: VT (25 and 250 mu g/ml), in contrast to ML, significantly enhanced phagocytosis and burst activity. VT-rich mistletoe extracts also exerted significant effects. In a ddition E.coli-activated granulocytes positively stain with Annexin-V and p ropidium iodide only due to 250 mu g/ml VT incubation, suggesting that at t his concentration burst activity was induced by the physiological activity of granulocytes after microbial ingestion and also by cytotoxic effects. Co nclusion: Viscotoxins exert yet unknown strong immunomodulatory effects on human granulocytes, which might be of benefit for tumour patients, in addit ion to their cytotoxic properties.