Human alveolar macrophages: wheat germ agglutinin-dependent tumor cell killing

Human alveolar macrophages (AM) obtained by bronchoalveolar lavage from healthy donors were examined for ability to cause lectin-dependent tumor cell killing. Of five plant and two animal lectins tested, only one lectin, wheat germ agglutinin (WGA), induced significant and reproducible lectin-dependent macrophage-mediated cytotoxicity (LDMC) against human bladder cancer (T-24) cells. There was no significant difference between the LDMCs of AM and blood monocytes. All 6 tumor cell lines tested were sensitive to various extents to LDMC induced by WGA. Quantitative analysis with WGA-FITC conjugate showed the presence of various levels of receptors for WGA on the surface of AM, monocytes and tumors. A relatively good correlation was found between the sensitivities of the tumor cells to LDMC mediated by AM and the numbers of receptors for WGA. Pretreatment of AM or monocytes with LPS did not affect their LDMC. These results indicate that a plant lectin, WGA which binds to both human AM and tumor cells, renders human AM cytotoxic to allogeneic tumor cells by a different mechanism(s) from that involved in the nonspecific tumor cytotoxicity of activated macrophages.