Factors affecting suppressor cell activity in tumor-allosensitized mice.

Adult C57BL/6 mice inoculated with P-815 mastocytoma cells developed splenic suppressor cells. These suppressor cells were assayed in mixed lymphocyte cultures. Suppressor cells appeared earlier and became more active after sensitization with low doses of allogeneic tumor. After low doses of tumor cells, the suppressor cell activity developed before cytotoxic activity, whereas after higher doses of tumor cells, suppressor and cytotoxic activity appeared simultaneously. The suppressor cells were not H-2 restricted but did express their activity stronger in the presence of the specific (H-2d) alloantigen. Neonatally thymectomized adult C57BL/6 mice failed to develop splenic suppressor cell activity after tumor allosensitization. This suggested that the thymus is a source for suppressor precursor cells. These precursor cells remained active in the spleen up to 3 1/2 months after adult thymectomy. Suppressor factor was released in cultures of tumor-allosensitized spleen cells. The presence of a specific (H-2d) alloantigen improved the relase of suppressor factor (SF). Cultures of tumor-allosensitized spleen cells, enriched for T-cells, contained more SF. SF was not H-2 restricted or antigen-specific.