ACTIVATION OF HUMAN GAMMA-DELTA T-CELLS BY HEAT-TREATED MISTLETOE PLANT-EXTRACTS

Various microorganisms including mycobacteria, other bacteria, and par asites such as Plasmodium falciparum are known to activate human gamma delta T-cells in vitro. In this study, we demonstrate that heat-treat ed (but not untreated) mistletoe extracts similarly stimulate human ga mma delta T-cells during in vitro culture. The responding T-cells expr ess the variable T-cell receptor elements V gamma 9 and V delta 2. The gamma delta-stimulating activity of heat-treated mistletoe extracts i s sensitive to treatment with alkaline phosphatase but not with protei nase K, indicating that the ligands are non-proteinaceous phosphate-co ntaining compounds. Mistletoe-derived ligands share these features wit h the previously defined mycobacteria-derived ligands for gamma delta T-cells.