SUPPRESSION OF MIXED LYMPHOCYTE RESPONSE IN MICE BEARING PRIMARY TUMORS INDUCED BY MURINE SARCOMA VIRUS

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Abstract
Mixed lymphocyte culture (MLC) responses of spleen cells from mice bearing tumors induced by murine sarcoma virus of the Moloney type (MSV) against allogeneic spleen cells were markedly depressed, as estimated by 3 parameters: lymphoblast counts, 3H-thymidine incorporation (TI) and cell-mediated lysis (CML). While all 3 parameters were depressed in comparison to the normal controls, TI was depressed to a greater degree than lymphoblast counts and CML. MSV spleen cells also had a suppressive effect on the MLC responses of normal spleen cells in 3rd party type experiments. The cells mediating this effect were radioresistant non-T [thymus-derived] cells, which were removed by adherence columns and inactivated by carrageenan. These data suggested that the suppressor cells were macrophages. Serum from MSV tumor-bearing mice had a greater suppressive effect than normal mouse serum. The suppressor cells and the suppressive serum factors may play an important role in the immunosuppression observed in tumor-bearing hosts.