Solid tumor-derived target cell susceptibility to macrophages and natural killer/natural cytotoxic cells in the rat

Cytotoxic capacity of rat macrophages (Mø) and natural killer (NK)/natural cytotoxic cells (NC) against adherent growing, solid tumor-derived target cells was evaluated, modulating the activation status of effector cells and growth conditions of target cells.Testing a panel of target cells, cytotoxicity of NK/NC and Mø was strikingly correlated so that besides of target-cell binding structures basic lysability seems to be of influence with respect to cytotoxicity rates. Varying the in vivo growth conditions of target cells altered their lysability by Mø and NK/NC cells in the sense that ascitic versus subcutaneously (sc) grown tumors were more resistant to lysis. On the other hand, in vitro culturing did not influence susceptibility for Mø, but with some tumor lines increased lysis by NK/NC cells was observed.In the rat, the activation status of Mø and NC was not age-dependent, and NK cell activity only declined slowly with age. But cytotoxic potential of Mø obviously presents a strain characteristic, different from NK/NC cell activity, only the latter two correlating in different rat strains. Experiments to augment natural cytotoxic capacity revealed that application of Corynebacterium parvum (CP) activated Mø and NK/NC cells, while sc tumor implantation only resulted in increased NK/NC cell cytotoxicity, leaving Mø activity unaltered.