Modulation of interleukin-15-induced human neutrophil responses by the plant lectin Viscum album agglutinin-I

The plant lectin Viscum album agglutinin-I (VAA-I) and the interleukin-15 ( IL-15) cytokine are two molecules with potential therapeutic properties kno wn to modulate neutrophil functions when used separately. This study was co nducted in order to better understand the mode of action of VAA-I and to el ucidate how VAA-I could modulate IL-15-induced neutrophil responses. We fou nd that VAA-I cannot induce phosphorylation events in human neutrophils. Ho wever, it enhances phagocytosis by itself without altering IL-15-induced ph agocytosis. VAA-I was found to reverse the ability of IL-15 to delay neutro phil apoptosis and this was correlated with an inhibition of IL-15-induced de novo protein synthesis. In addition, we also found that IL-15 cannot rev erse or attenuate the caspase-induced gelsolin fragmentation observed durin g apoptosis as assessed by immunoblotting. We conclude that VAA-I can be us ed to modulate some, but not all, IL-15-induced neutrophil responses and th at it acts independent of phosphorylation events. (C) 2001 Academic Press.