Natural Killer Cell Activity in a Population of Leukemia-Prone Wild Mice (mus Musculus).

Natural cell‐mediated cytotoxicity against YAC‐1 targets was measured in splenocytes from leukemiaprone wild mice trapped near Lake Casitas (LC) in southern California. Cytotoxicity was mediated by cells that were non‐adherent to nylon wool, non‐phagocytic and resistant to thy‐1.2 antiserum plus complement. Natural MuLV viremia in LC mice did not impair splenic cytotoxicity against YAC‐1 target cells. Cells infected with amphotropic and ecotropic MuLV of wild mouse origin were not appreciably lysed by LC splenic effectors. Although variable levels of cytotoxicity were detected against YAC‐1 by normal LC spleen cells, consistently low levels of cytotoxicity against allogenic LC lymphoma, sarcoma and carcinoma targets were found using the same splenocytes. These results indicate that LC mice possess splenocytes with the characteristics of natural killer (NK) cells as defined in inbred mice. The resistance of LC‐derived targets to lysis by LC NK cells suggests that NK cells may not be involved in natural tumor immunosurveillance or that the development of spontaneous tumors may involve escape from NK‐mediated effector mechanisms.