Modulation of cellular and humoral immune responses during exposure of healthy individuals to an aqueous mistletoe extract.

Mistletoe extracts have been shown to exert immunomodulatory properties. However, little is known about changes in different immunological parameters during therapy. Aim of our study was, therefore, to investigate the influence of subcutaneous treatment in 8 volunteers who were exposed to an aqueous mistletoe extract (Viscum album Mali; VM) for 8 weeks. During in vivo exposure, VM induced the production of anti-ML-1 antibodies of the IgG-type. A pronounced proliferation of peripheral blood mononuclear cells (PBMC) could be observed in 6 volunteers. However, the activity and time of maximal response varied from one individual to the other. There was no correlation between the cellular and the humoral reactivity and different antigens present in this mistletoe extract may be operative at different levels of the immune system. In order to define more precisely the type of immune response, cytokines were measured in the supernatants of VM-stimulated cell cultures. VM induced the secretion of Th1- (IFN-gamma) or Th2- (IL-4) related cytokines and also the release of TNF-alpha and IL-6. All these different immunological phenomena can be best explained by presentation of mistletoe-related antigens to T- and B-cells via antigen presenting cells in the draining lymph nodes.