Natural cytotoxic cells against solid tumors in mice: a comparison with natural killer cells

From the comparison of the similarities and differences between lymphoid cells from normal mice capable of killing targets in vitro, derived from solid tumors (termed natural cytotoxic or NC cells), and those cells capable of killing target cells in suspension, mostly derived from lymphoid tumors (natural killer or NK cells), it is apparent that natural cell-mediated cytotoxicity (CMC) is mediated by a family of effector cells of still undefined lineage (i.e., neither T, B, nor macrophages) of which NC and NK cells may be examples. Natural CMC has unique properties not shared by conventional specific immune CMC and, although the structures in the target cells recognized by NC-NK cells are still undefined, they appear to be related to simple sugars of the membrane. Since the properties of both NC and NK cells appear to correlate well with in vivo resistance or susceptibility to tumors as well as with early responses to some infectious agents, it is probable that natural CMC may represent an early defense mechanism of physiological importance.