Dept. of Microbiology, School of Medicine, East Carolina University, Greenville, NC.

The responsiveness of spleen cells from C57BL/6J mice to various immunogenic stimuli was examined during the progressive growth of a poorly immunogenic fibrosarcoma T241. A strong correlation was observed between the progressive tumor growth and the depression of response to Concanavalin A, lipopolysaccharide, sheep red blood cells, and alloantigens in mixed lymphocyte reaction and cell-mediated lympholysis (CML). The maximum depression of these immune responses occurred when the animals had grown tumors for 3-4 weeks. Furthermore, serum from these animals collected 20 days after tumor transplantation was highly immunosuppressive. The possible mechanisms of tumor-induced immunosuppression have been discussed.