Demonstration of specifically sensitized lymphocytes in patients treated with an aqueous mistletoe extract (Viscum album L.)

Summary

Lymphocytes of 25 patients treated with an aqueous mistletoe extract (Viscum album L.) for up to 6 months (group 1), up to 2 years (group 2), and more than 2 years (group 3) were examined in 3- and 7-day cultures for specifically sensitized lymphocytes. The whole extract (HM), the lectin-polysaccharide fraction (HM-LP), and the ‘viscotoxin’ fraction (HM-V) were added at concentrations ranging from 0.5 μg to 12.5 mg extract/ml. Lymphocytes from four of the nine group 2 patients and five of the ten group 3 patients reacted specifically with HM and HM-LP at an optimal dose of 5.0 mg/ml, but did not react with HM-V. Stimulation indices varied between 1.6 and 16. In the patients of group 3 this effect was observed only when their lymphocytes were costimulated in the 3-day cultures with phytohem-agglutinin (PHA), in contrast to the four patients of group 2 who reacted only in the 7-day cultures with HM-LP without PHA co-stimulation.

Patients' lymphocytes had to be protected from mistletoe lectin-induced cytotoxicity by the addition of their own sera containing anti-mistletoe lectin antibodies. Lymphocytes from tumor patients (n=18) never treated with mistletoe extracts and healthy individuals (n=18) showed no specific proliferative response when tested in 3- and 7-day cultures. The production of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-γ (IFN-γ) was measured in the supernatants of lymphocyte cultures from all 25 patients and 36 controls exposed to HM, HM-LP, and HM-V in 3- and 7-day cultures. An increase of GM-CSF (up to 140%) was found only in those patients who responded specifically to the extract, while none of them produced increasing amounts of IFN-γ. These findings imply that a sub-population of T-helper cells may have been stimulated in the course of mistletoe therapy.