Charakterisierung der immunmodulatorischen Wirkung von Mistelpräparaten auf Zellen des Immunsystems von Rindern

Mistletoe preparations (Viscum album) have immunomodulatory properties for human and murine cells. Up to now, no studies have been performed with bovine immune cells. Therfore this work focuses on such effects concerning three different mistletoe preparations (ABNOBAviscum Mali-2, Fraxini-2 und Pini-2) containing varying contents of mistletoe lectins and viscotoxins. The investigations covered the induction of cellular death, cellular proliferation and other functional properties of bovine blood leukocytes (neutrophilic granulocytes, PMN, and mononuclear cells, MNC). Inhibition assays revealed that specific sugars compete with binding of mistletoe compounds, proving that mainly lectins account for the binding to bovine leukocytes. Labelling studies proved that mistletoe lectins bind with comparable affinity and strength to all bovine leukocyte subsets. Mistletoe products reduced significantly the numbers of viable bovine mononuclear cells. The most potent appeared to be V. Fraxini and V. Mali, killing the cells significantly at 0.15 µg/mL, followed by V. Pini (effective concentration: 150 µg/mL). Neither MNC monoculture nor in coculture with PMN had effects on the killing induced by V. Pini. In cocultures V.Fraxini and V. Mali revealed a cytotoxic effect at a concentration higher than 1.5 µg/mL. The cytotoxic effect could be inhibited significantly by mistletoe lectin-specific sugars. Cytotoxicity at 1.5 µg/mL affected significantly CD14+ monocytes and CD8+ T cells, and at higher concentrations (5µg/mL) also CD4+ T cells and nonT/non-B cells. In contrast none of the mistletoe products showed cytotoxic effects on PMN whether they were cultured alone or in combination with MNC. In addition, the generation of reactive oxygen species after receptor independent stimulation with phorbol myristate acetate was only moderately reduced by high concentrations of mistletoe products. No effects were seen on the Fc receptor-dependent stimulation with opsonised bacteria. The in vitro transmigration towards recombinant human CXCL8 remained largely unaffected, whether mistletoe products were used in combination with cells in the upper chamber or with rhCXCL8 in the lower chamber. Quantitative flow cytometric analysis did not reveal a proliferation-enhancing effect of subapoptotic mistletoe product concentrations for in vitro stimulated MNC. However, analysis of cellular division rates after carboxy-fluorescein-succimidyl-ester labelling revealed that a low V. Fraxini concentration (0.15 µg/mL) enhanced the cellular division rate for superantigen-, but not for mitogen-stimulated MNC. These still preliminary data are pointing towards a modulation of the T-cell receptor-mediated stimulation by mistletoe lectins. The observed effects on MNC are in part comparable to published findings in humans, whereas the complete lack of PMN modulation seems to be unique for cattle. The differential modulation of activation, proliferation and apoptosis of cells of the adaptive immune response indicate that mistletoe products interfere with key structures in activating and sustaining immunological responses in cattle – eventually advantageous as novel adjuvant compounds in vaccines or as mediators of immune polarization as successfully proved in murine models.