Mistletoe extract-induced effects on immunocompetent cells: in vitro studies

Cytotoxic as well as immunomodulatory effects of mistletoe extracts and their components have been described and seem to depend upon the host tree, the manufacturing process and the composition of the different components present in the extracts. In vitro studies showed that a fermented mistletoe extract derived from Viscum album L. grown on pine trees was less cytotoxic to peripheral blood mononuclear cells (PBMC) than other preparations. This finding could be related to its very low content of mistletoe lectins. Furthermore, this extract stimulated PBMC from healthy and especially allergic donors who had never received any mistletoe treatment. By analysing these in vitro reactions, an involvement of CD4+ T helper cells and CD14+ monocytes/macrophages was observed, suggesting an interaction of the specific and nonspecific immune system. In the supernatants of stimulated PBMC from healthy individuals, type-1 (interferon-gamma and interleukin-2) and type-2 (interleukin-4 and interleukin-5) associated cytokines were detected in about 20%. In patients with colorectal tumours, however, reduced frequency, suggesting a functional impairment of certain immunocompetent cells in these patients. These studies may help to evaluate properties of the natural and the specific immune system.