In vitro inhibition of lymphoproliferative responses to tumor associated antigens and of lymphoma cell proliferation by rat splenic macrophages.

Spleens from W/Fu rats bearing a syngeneic progressively growing (C58NT)D tumor contain cells which can inhibit lymphoproliferative responses in a mixed lymphocyte-tumor interaction designed to demonstrate suppressor activity. Spleens from rats having rejected (C58NT)D tumors also contained suppressor cells but to a lesser degree. The growth inhibition assay, which measures inhibition of proliferation of tumor cells, was evaluated as a simple assay system to screen for suppressor cell activity. The effector cells in both assays had the same characteristics, indicating a predominant role of macrophages. Normal rat spleens were found to contain growth inhibition activity which led to the demonstration of suppressor cell activity in spleens of normal animals. Removal of suppressor cells from the spleens of immunne rats results in consistently higher lymphoproliferative responses to tumor associated antigens on the tumor cells.