Powerful immunosuppression mediated by interleukin 2-activated, nonantigen-specific, or H-2-restricted THY-1⁺ CD8⁺ cells

Normal spleen cells cultured in high or low concentrations of interleukin (IL) 2 for 3 days contain Thy-1⁺ CD4^- CD8⁺ cells that powerfully suppress primary but not ongoing or active lymphocyte responses. The precursors of these cells are Thy-1⁺AGM-1^- and are absent or present in greatly diminished numbers in athymic and scid mice. Suppression is neither antigen nor H-2 restricted and apparently results from reversible inactivation of resting lymphocytes. Comparable Thy-1⁺ CD8⁺ suppressor cells were also recovered from normal spleen cells cultured for 3 days with anti-CD3 antibody without added IL-2, indicating that these cells can be activated during the course of immune responses. Such cells may prevent local recruitment/activation of lymphocytes specific for new epitopes that may be expressed sequentially by proliferating tumor cells or infectious organisms.