Variable sensitivity of lymphoblastoid cells to apoptosis induced by Viscum album Qu FrF, a therapeutic preparation of mistletoe lectin.

BACKGROUND

Viscum album (VA) Qu FrF preparation consists of an aqueous extract of Viscum album, the European mistletoe. It has cytotoxic and immunomodulatory properties that support its usefulness in cancer therapy. However, only little information is available on the interaction between mistletoe lectin (ML) and the humoral compartment of the immune system.

METHODS

Inhibition of proliferation of cells was performed by incorporation of (3)H-thymidine, and cell viability was assessed by the uptake of propidium iodide. Detection of Bcl-2 and related molecules was performed by SDS-PAGE followed by immunoblotting.

RESULTS

We demonstrated that B lymphocyte lines are insensitive to VA Qu FrF-induced apoptosis. We showed, using Fas-sensitive and Fas-resistant cell lines, that VA Qu FrF-induced apoptosis is Fas independent. In both B and T lymphocytes, treatment of the cells with VA Qu FrF was associated with decreased levels of Bcl-2 and Bcl-X.

CONCLUSIONS

Our results suggest that B lymphocyte depletion is not involved in the modulation of humoral immunity by ML. These observations should be of value in appropriate designing of cancer therapy using compounds containing mistletoe extracts.