Biochemical characterization of a component in extracts of VISCUM ALBUM enhrancing human NK cytotoxicity

Journal/Book: Immunopharmacology 17, 11-18. 1989;

Abstract: Enhancement of human NK cytotoxicity in the presence of fresh Viscumalbum extract and some commercial V. album extracts Iscador correlatedstrictly with an increased formation of lytic effector cell/K562 tumorcell conjugates in the single-cell assay. Both activities werecompletely destroyed by pretreatment of V. album extracts withpectinase, hemicellulase, amyloglucosidase and alpha-glucosidase, butnot with proteases and RNase, i.e., the activities are linked to apolysaccharide. The active component in V. album extract wasnon-dialysable at a molecular weight cutoff of 10,000. Inhibition ofboth activities was observed with D-galacturonic acid, poly-galacturonicacid and pectins. The site of galacturonic acid-specific interactioncould be identified on the effector cells. The rate of effectorcell/tumor cell conjugate formation in the presence of V. albumextracts, as well as the abrogation of both activities by pretreatmentof V. album extracts with exoglycosidases specific for sugars other thangalacturonic acid indicated an action of the NK cytotoxicity-enhancingcomponent on the basis of a bridging mechanism. However, no conclusiveresults could be obtained for the structural specificity of the siteinteracting with the target cells. Author.

Keyword(s): BINDING-SITES

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