Adsorption of suppressor cell activity on mouse macrophage monolayers.

Suppressor cell activity is high in the spleen of C57BL/6 mice sensitized to the allogeneic P-815 mastocytoma. The suppressor cells inhibit proliferation of normal mouse spleen cells in mixed lymphocyte cultures. Preincubation of tumor-allosensitized spleen cells on monolayers of syngeneic or allogeneic macrophages reduces suppressor activity. Preincubation on monolayers of spleen cells does not affect suppressor activity. Suppressor cells can be retrieved from the macrophage monolayers used for adsorption. Heat-killed macrophages fail to adsorb out suppressor cell activity. Incubation of tumor-allosensitized spleen cells on syngeneic macrophage monolayers does not reduce cytotoxic cell activity. Removal of suppressor cell activity by macrophage adsorption restores helper activity of tumor-allosensitized spleen cells. These results demonstrate that suppressor cell activity can be reduced by contact with macrophages and point to an additional role for the macrophage in regulating the immune response to tumors.