Activation of human gamma delta T-cells by heat-treated mistletoe plant extracts.

Various microorganisms including mycobacteria, other bacteria and parasites such as Plasmodium falciparum are known to activate human gamma delta T-cells in vitro. In this study, we demonstrate that heat-treated (but not untreated) mistletoe extracts similarly stimulate human gamma delta T-cells during in vitro culture. The responding T-cells express the variable T-cell receptor elements V gamma 9 and V delta 2. The gamma delta-stimulating activity of heat-treated mistletoe extracts is sensitive to treatment with alkaline phosphatase but not with proteinase K, indicating that the ligands are non-proteinaceous phosphate-containing compounds. Mistletoe-derived ligands share these features with the previously defined mycobacteria-derived ligands for gamma delta T-cells.