Cloned human T lymphocytes with lymphostimulatory capacity preferentially activate suppressor cells

A proportion of cloned T cells derived from allogeneic mixed leukocyte cultures (MLC) was found to stimulate rapid primary, but not secondary, lymphoproliferative responses of autologous as well as allogeneic peripheral blood mononuclear cells (PBMC). Of eight major histocompatibility complex (MHC) class II-specific monoclonal antibodies (mAb), the reagent TU39 (which preferentially inhibits allostimulation by SB- rather than DR- or DC-associated determinants) most strongly inhibited stimulation by these clones. MAb specific for DC or DR molecules inhibited weakly or not at all. Stimulatory, but not nonstimulatory, clones were found to be strongly suppressive when titrated directly into MLC. Suppression was no MHC restricted, was radioresistant (20 Gy) and was not abrogated by the addition of partially purified interleukin 2 to the test cultures. Transfer of PBMC cocultured with stimulatory, but not with nonstimulatory, clones into a second MLC resulted in its strong suppression, suggesting that a suppressor effector population had been "induced" by the clones. These results are consistent with the hypothesis that SB-like, rather than DR or DC, determinants present on the surface of certain activated T cells are intimately involved in the regulation of cellular immune responses by rapidly inducing suppressor effector cells in normal lymphocyte populations.