The generation of an allospecific suppressor factor in culture.

When mouse spleen cells were stimulated by irradiated allogeneic cells in a mixed lymphocyte culture for 96 hours, allospecific suppressor cells were generated that could inhibit the replicative processes when transferred to another MLR. When the primed cells were purified on Ficoll and incubated alone for another 24 hours, they released into the medium a subcellular factor which could also suppress MLR allospecifically. Evidence is provided that the cells which generate this factor arise by cooperation of at least two types of T-lymphocytes, one of which is the progenitor of the suppressor cell and the other an essential accessory cell. Adherent cells were shown to be also essential for the priming of suppressor lymphocytes.