Suppressor cells in the spleen of tumor-allosensitized mice

C57BL/6 mice were sensitized i.p. with 20 X 10(6) P-815 mastocytoma cells. Spleen and lymph node cells from these tumor-allosensitized mice become hyporesponsive in mixed-lymphocyte culture. The hyporesponsiveness appears to be due to the presence of suppressor cells. These suppressor cells can be demonstrated by their ability to inhibit the mixed-lymphocyte culture reactivity of normal mouse spleen cells. Suppressor activity in the spleen of tumor-allosensitized mice remains long after cytotoxic activity disappears. The mixed-lymphocyte culture suppressor cells do not adhere to glass and are cortisone resistant, X-irradiation resistant, anti-immunoglobulin serum resistant, but are anti-theta (Thy 1.2) serum sensitive. Adsorption of tumor-allosensitized spleen on specific allogeneic monolayers removes cytotoxic but not suppressor cells. On the basis of the kinetic data, cortisone sensitivity, antisera sensitivity, and adsorption results, we conclude that the suppressor cell is a thymus-derived lymphocyte that is separate from the cytotoxic thymus-derived lymphocyte.