Induction of human monocyte-mediated tumor cell killing by a plant lectin, wheat germ agglutinin.

Human peripheral blood monocytes from healthy donors were separated by discontinuous gradient centrifugation and adherence to yield highly purified adherent cell populations (greater than 99% monocytes). Five different plant lectins were tested for ability to induce lectin-dependent monocyte-mediated cytotoxicity (LDMC). Only one lectin, wheat germ agglutinin (WGA), induced significant and reproducible LDMC activity. All the tumor target cells tested were sensitive to variable extents to cytotoxicity mediated by WGA-treated monocytes. Pretreatment of monocytes with WGA did not result in development of LDMC. N-Acetylglucosamine, which specifically binds WGA, inhibited WGA-dependent monocyte-mediated cytotoxicity. Treatment of adherent monocyte-rich monolayers with monoclonal anti-natural killer cell antibody (anti-Leu-11b) and complement did not affect the LDMC activity induced by WGA. These results indicate that the plant lectin WGA, which binds specifically to both human monocytes and tumor cells, renders human blood monocytes cytotoxic to human tumor cells.