Immunoglobulin production in the autologous MLR: target of the suppressor-amplifier circuit.

A suppressor-amplifier circuit controlling the generation of plaque-forming cells has been demonstrated previously by us in the autologous mixed leucocyte reaction. Thus, after Leu-3+ dependent activation in an initial culture, radio-resistant Leu-2+, DR+ suppressor-amplifier cells can potently suppress Leu-3+ dependent generation of antibody forming cells, but only in the presence of fresh Leu-2+, DR- suppressor-effector cells. The target of this suppressor-amplifier circuit has been examined in a triple culture system. Suppressor-amplifier cells were activated in an initial culture; Leu-2+ cells were separated from this initial culture and transferred to an intermediate culture. After 72 h Leu-3+ helper T cells were separated from this culture and tested for their ability to support the generation of antibody-forming cells in a third culture. Such helper T cells were unable to support antibody synthesis when cultured with fresh B cells. In contrast, B cells from the intermediate culture could be activated to produce antibodies, when cultured with a fresh source of T cell help. These findings are consistent with the helper T cells being the target of the suppressor-amplifier circuit.