Suppressor cells in mice with murine mammary tumor virus-induced mammary tumors. I. Inhibition of mitogen-induced lymphocyte stimulation.

Suppressor cell activity was present in the glass-adherent fraction of spleen cells from C3H mice bearing murine mammary tumor virus-induced mammary tumors. These cells effectively suppressed the blastogenic response of syngeneic normal lymphocytes to concanavalin A (Con A). Suppression by the spleen cells from mammary tumor-bearing mice was not dependent on DNA synthesis. Removal of the suppressor cells from spleen cell suspensions of tumor-bearing mice was not dependent on DNA synthesis. Removal of the suppressor cells from spleen cell suspensions of tumor-bearing animals (TBA) by passage of the cells on glass wool columns increased the Con A response of the remaining cells by fourfold to eightfold. Characterization of the suppressor population indicated that the cells were also adherent to nylon wool but not to plastic and contained a significantly increased proportion of surface immunoglobulin-bearing and complement receptor-bearing lymphocytes. Depletion of macrophages and T-cells did not remove the suppressive activity from the spleens of the TBA. The results were consistent with the identification of the suppressor cell as a B-cell.