Spleen cells of C57BL/6J mice bearing a poorly immunogenic syngeneic tumor T241 have been shown to suppress the mitogen-induced proliferative responses of normal spleen cells. However, no suppressive effect of these cells was observed on the generation of cytotoxic cells following immunization in vitro against H-2 histocompatibility antigens. The suppressor activity disappeared rapidly after the removal of the primary tumor. Spleen cells of tumor-bearing mice also suppressed the mitogen-induced stimulation of normal spleen cells of mice of different H-2 loci. Removal of phagocytic cells with carbonyl iron treatment had very little effect on the suppressor activity. Suppressor activity was enhanced following fractionation of cells through nylon wool columns. The suppressor population was found to resist anti-immunoglobulin serum and complement treatment, but treatment with anti-thymocyte serum and complement drastically reduced the suppressor activity. These results indicate that cells with suppressor activity have characteristics of T-lymphocytes.

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Supported in part by National Cancer Institute Grant CA-13916.

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