Hosts of plasma cell tumors have a depressed primary antibody response. We have investigated the ability of cell homogenates and culture fluids from short-term cultures of spleen cells and tumor cells of mice bearing the MOPC-315 plasmacytoma to suppress the in vivo primary antibody response to sheep red blood cells. The homogenates and culture fluids of both MOPC-315 spleen cells and tumor cells suppress the antibody response in a dose-dependent manner. Culture fluids of spleen cells from tumor-bearing mice contain a 10,000- to 20,000-dalton immunosuppressive factor. Culture fluids of non-adherent tumor cells contain a high m.w. suppressor. Injection of the high m.w. tumor suppressive factor into normal mice induces the expression or appearance of host cells that secrete the 10,000- to 20,000-dalton immunosuppressor. The tumor suppressive factor, but not the spleen factor, causes an alteration of lymphocyte membranes such that the anti-DNP activity of the MOPC-315 myeloma protein can be detected on the circulating lymphocytes of injected mice.
This work was supported by United States Public Health Service Grant CA16835 and funds from the Mayo Foundation.