Localization of mistletoe lectins ML I-III in Viscum album L. by immunofluorescent and immunogold labeling

Abstract

Purpose: Because of their immunomodulatory and cytotoxic ffectsmistletoe extracts play an important role as phytotherapeuic adjuvants in cancer therapy.Mistletoe lectinsML I-III contribute ssentially to the in vivo activity of mistletoe preparations. They onsist of two chains: the B chain is necessary for binding to speific carbohydrate epitopes at the surface of target cells whereas he A chain is responsible for the inhibition of translation. The ocalization of bioactive lectins in Viscum album L. is of significance o understand the distribution and physiological role of lectins in he plant itself and to optimize the production of pharmaceutical reparations. Methods: The cellular distribution of lectins in different parts nd tissues of mistletoe plants was investigated by immunofluoescent labeling. Thin sections of leaves and internodes of shoots f Viscum album L. were treated with a monoclonal antibody irected against the A-chain of mistletoe lectins I–III. A secondary uorescent-labeled antibody was added and the sections were nalyzedby confocal laser scanningmicroscopy. Intracellular localzation of lectins was performed by immunogold labeling and ransmission electron microscopy. Results: The mistletoe lectins I–III in internodes were located ainly in cells of the parenchyma of the cortex, in sclerenchyma issue next to the vascular bundles and in the companion cells of he phloem. Especially in parenchyma cells of the third and fourth nternode a high content of lectins could be detected, whereas arenchyma cells of the leaves showed weak labeling only. Within arenchyma cells lectins could be detected inside of vacuoles, ostly in close contact with protein bodies. Conclusions: Mistletoe lectins are mainly located in shoots of he plant, whereas leaves only contain minor amounts of them. mmunolabeling could be shown to be a sensitive method for the xact localization of mistletoe lectins in plant tissues and may also e used to investigate the distribution and specific binding of ML –III in animal or human tissues. Acknowledgements: We thank Rottapharm|Madaus GmbH, oln, for financial support.