Immunosuppression in plasmacytoma: induction of suppressor cells.

Immunosuppression in BALB/c mice with plasmacytomas (PC) is, at least in part, due to increased suppressor activity of splenic adherent cells. A PC subcellular fraction rich in intracisternal A particles, previously shown to have an immunosuppressive effect in normal BALB/c mice, is now shown to exert this effect through the development of splenic suppressor cells. The splenic suppressor cells induced with this subcellular fraction were found to be radioresistant adherent macrophages that suppressed the immune response of normal splenic cells to sheep erythrocytes through a diffusible factor, but did not influence their polyclonal IgM secretion ater LPS stimulation in vitro. These characteristics are identical to those of the naturally occurring suppressor macrophages in mice with PC. Whether the induction of suppressor cells is due to the intracisternal A particles themselves or a factor co-purified with them, remains to be established.