Antigen-antibody complexes generate Lyt 1 inducers of suppressor cells

Pretreatment of H-2b mice with KCl-extracts of an H-2d tumor (L1210) together with L1210 antibody rendered the mice incapable of mounting an effective immune response to viable L1210 tumor cells. This specific immunosuppression was associated with inhibition of macrophage functions, which could be used to quantitate the level of suppression. Lyt 1 cells (but not Lyt 2 cells) from either the spleen or thymus of mice pretreated with antigen-antibody complexes could adoptively transfer the suppressed state to normal mice. The Lyt 1 cells that transferred the suppression were resistant to low (20 mg/kg) doses of cyclophosphamide (Cy) but required a Cy-sensitive precursor and/or amplifier cell to be activated. Once activated, they required a Cy-sensitive Lyt 1 2 3 acceptor cell in the normal recipient to effectively suppress the adoptive host's macrophages. Our results indicative that immune complexes in concert with a Cy-sensitive T cell generate Cy-resistant Lyt 1 inducers of suppression. These in turn activate normal thymic or peripheral Lyt 1 2 3 acceptor cells, resulting in the generation of effector suppressor T cells. These suppressor cells are most likely the proximate cause of the inhibition of macrophages we have observed in vivo.