Suppressor cells: dependence on assay conditions for functional activity.

Spleen cells educated in vitro with sheep red blood cells (SRBC) suppressed the plaque-forming cell response of Mishell-Dutton assay cultures challenged with optimal doses of SRBC. Changing conditions in the assay cultures changed the effect educated cells had on the assay culture responses. For example, educated cells helped rather than suppressed assay cultures of suboptimal numbers of spleen cells. Similarly, augmentation resulted upon addition of educated cells to assay cultures challenged with suboptimal doses of SRBC. Such a reversal of regulatory effects was not observed when assay cultures were challenged with supraoptimal antigen doses. Educated cells helped assay cultures of B spleen cells, and the addition of normal T cells reinstated suppression. Furthermore, maintenance of assay cultures under stationary rather than the usual rocking conditions allowed educated cells to help rather than suppress the antibody response of assay cultures. These results show that when the response of the target population (assay cultures) is low, the regulator (educated) cells augment the response, and vice versa, supporting the hypothesis that the effect regulator cells produce depends on the activity of the cells they regulate.