ABSTRACT
Lectins from different types of mistletoe (Viscum album, VA) have cytotoxic and immunomodulatory properties that may be relevant in the inhibition of tumor growth. The mechanism of this anti-tumoral activity remains unknown, although recent investigations point out the induction of anti-tumoral cytotoxic T cell activation. In this study therapeutically available mistletoe extracts (Iscador) prepared from Quercus (VA-Q), apple (Malus, VA-M) or pine (Pinus, VA-P) were used to investigate their capacity to induce tumor regression through the modulation of another T helper-1 (Th-1)-mediated anti-tumoral activity: the activation of macrophages. Macrophages are essential targets for both pro- or anti-inflammatory drugs and constitute an essential member of the anti-tumoral immune response. Freshly isolated human monocyte-derived macrophages are activated and various VA extracts are directly incorporated to cultures to assay their properties on the inflammatory and/or tumor cytotoxic responses. The data indicate that immunomodulatory activities of VA extracts differ according to their origin. VA-M and VA-P were able to increase anti-tumoral activity of activated human macrophages, with a possible role for nitric oxide in this effect.
