Induction of tumor associated macrophage-mediated lysis of autologous tumor cells by lectins.

Lectin dependent cell mediated cytotoxicity (LDCC) to autologous tumor cells (ATC) by the tumor associated macrophages (TAM) was studied by 4 h 51Cr release assays at early and late stages of growth of a murine transplantable ascites tumor, S-180, in presence of different concentrations of wheat germ agglutinin (WGA) and Concanavalin A (Con A). Induction of LDCC by the unstimulated resident macrophages (RM) to S-180 tumor cells was also assayed. Both WGA and Con A induced significant tumoricidal activity in the TAM at different states of activation and in RM in a dose-dependent manner, the activated TAM showing expression of cytotoxicity with the lowest doses of the lectins used. Addition of N-acetylglucosamine (NAcGle) or D-mannose (D-man) in the assay completely inhibited LDCC induced by WGA and Con A, respectively. Effector-target contact alone not sufficient for inducing lysis in LDCC was evident from the observations that low doses of the lectins augmented target binding by the inactivated TAM and RM with no subsequent cytolysis.