Natural cytotoxic cells against solid tumors in mice: blocking of cytotoxicity by D-mannose.

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Abstract
Natural cytotoxic (NC) and natural killer (NK) cells have been defined by their ability to lyse certain solid or lymphoid tumor targets in vitro, without prior sensitization. An attempt to characterize the structures involved in the effector-target recognition leading to tumor cell lysis is described. Addition of the monosaccharide D-mannose to the NC cell assay significantly blocked cytotoxicity of the T [thymus-derived] fibrosarcoma Meth A cells target by the effector cells at 50 mM and lower concentrations. D-Galactose showed blocking activity only at 50 mM. L-Fucose, D-glucose and N-acetyl-D-glucosamine did not affect NC cell cytotoxicity at similar concentrations. All of the sugars tested inhibited NK cell lysis of the [mouse Moloney lymphoma virus-induced] YAC-1 cells target. None of the sugars affected killing of the appropriate target by allosensitized cytotoxic T [thymus-derived] lymphocytes. The blocking of NC-mediated cytotoxicity was not due to a direct toxic action of the sugars on the effector cells. In the NC system, recognition probably involves lectin-like structures with a specificity for D-mannose (or D-galactose or both); in the NK system, such lectin-like structures are less restricted. Such structures appear not to be involved in the specific cytotoxicity mediated by T cells.