The plaque-forming-cell (PFC) response of human blood lymphocytes. II. PFC response by mixtures of allogeneic lymphocytes cultured with formalin-treated staphylococci

Formalin-treated Staphylococci (FSA) induce anti-SRBC PFC in cultures of human lymphocytes. Regulation of the PFC response induced by FSA in cultures containing lymphocytes from two allogeneic donors was studied. The PFC response observed in such cocultures could not be predicted from the responses of lymphocytes from the two donors cultured individually. The PFC response of approximately one half the cocultures was less than expected. The remaining cocultures generated more PFC than expected. The depression or augmentation in the PFC response which was observed in cocultures was reproducible when lymphocytes from the same pair of donors were cocultured. Cocultures containing lymphocytes from identical twins generated the expected PFC response. The data suggest that suppressor or helper activity may be generated during a “two-way” allogeneic mixed lymphocyte reaction (MLR). Much less deviation from the expected PFC response was observed during a “one-way” MLR. Anti-Ia antiserum treatment of either donor's lymphocyte population tended to eliminate the deviation from the expected PFC response in coculture. The data suggest that a feedback loop, involving cells from both donors, may be operating in the “two-way” MLR, which leads to the generation of suppressor or helper activity.