Diffusible suppressor factor from splenic macrophages in murine plasmacytoma.

The immunosuppressive effect of splenic macrophages (M phi) in mice bearing plasmacytoma was previously shown to be mediated by a diffusible factor. This diffusible suppressor factor (DSF) was found to be non-dialysable and sensitive to heating to 56 degrees C and to the proteolytic action of trypsin. The suppressor factor could be removed from culture supernatants by binding to ligands that specifically bind to corresponding myeloma proteins. DSF from splenic suppressor M phi of mice bearing MOPC 315 was capable of binding dinitrophenyl L-lysine, and that from mice bearing MOPC 104E, dextran S. The suppressor factor apparently cross-reacted with anti-idiotypic antibody to the corresponding myeloma protein, but did not interact with anti-isotypic antibody to mouse immunoglobulins (Ig). A higher concentration of mouse Ig than that found in DSF preparations did not have a suppressive effect. Metabolic inhibitors for RNA and protein, but not DNA synthesis effectively blocked the production of DSF. These findings suggest that DSF is a non-Ig protein that may have a structural similarity to myeloma idiotype. Continuous RNA and protein synthesis is required for the elaboration of DSF by splenic suppressor M phi in cultures.