Suppressor activity of splenic macrophages in murine plasmacytoma (PC) is inhibited by PC specific ligands.

Spleens of BALB/c mice with plasmacytoma contain macrophages (M phi) which were found to suppress the in vitro immune function of normal splenic cells through a diffusible factor. The suppressor activity of these macrophages was reversibly inhibited by ligands specific for the corresponding PC globulin, but not by anti-idiotypic antibody. Anti-idiotypic antibody with complement, however, abrogated the suppressor function, presumably by cytotoxicity. Anti-isotype with complement was ineffective. These findings suggest binding of ligand to a surface receptor of the suppressor M phi that although clearly not PC globulin, may be structurally similar to the PC idiotype. These receptors are retained in 3 day cultures of macrophages and are not removed by intensive washing. Ligand binding appears to modulate the suppressor function of M phi through blocking of the production of diffusible suppressor factor.