Immune status of mice tolerant of living cells. III. Presence and evolution of cells cytotoxic to the tolerated strain.

Spleen cells from CBA mice neonatally rendered highly tolerant to A/Jax (keeping a skin graft in perfect shape for more than 1 year and without detectable hemagglutinating or cytotoxic antibodies) contain cells cytotoxic for YAC 222 (A/Jax) in Cr release assay. The degree of the cytotoxicity depends on the age of the mouse, following a curve lower than, but parallel to, the one followed by the cytotoxicity of cells from CBA rendered immune by injecting them with A/Jax cells 1 week previously. The maximum of the cytotoxicity curve is reached during the 9th and 10th weeks. Normal CBA cells themselves are moderately cytotoxic to YAC 222. This "natural" cytotoxicity, significantly less intense and presumably directed against Moloney virus-related determinants, does not follow the same time pattern. The cytotoxic indices from both immune and tolerant cell populations are significantly reduced by CBA and anti-A/Jax immune serum. The tested sera of the tolerant mice did not contain hemagglutinating or in vitro-blocking antibodies in the Cr release assay (only the sera from unsuccessfully treated mice, having rejected their skin grafts, had some degree of blocking activity). However (and in agreement with previous experiments), these sera often contained synergistic hemagglutinins and in vivo enhancing properties of A/Jax tumors (Sal) grafted on CBA recipients.