The effects of erythrocyte-absorbed H-2 alloantisera on mixed lymphocyte culture reactions.

One-way mixed lymphocyte culture reactions were inhibited by the addition of H-2 alloantisera directed against the stimulator cell type. The sera retained their original inhibitory activity after the removal from them of conventional H-2K antibodies by exhaustive absorption with erythrocytes. The absorbed antisera had specificity for Ia but not H-2 antigens thereby indicating that the inhibitory activity of the sera is a function of antibodies against I region products. H-2 and Ia alloantisera directed against the responder cell type did not specifically inhibit culture reactions: they either had no effect or they apparently increased stimulation. This increase appeared to be immunologically specific, at least in part, and to require some heat-labile normal serum component for its elicitation. It is concluded that treatment of responder cells inactivates or destroys some normally inactive or inhibitory subpopulation such that the remaining cells respond better to allogeneic stimulation. Both the anti-stimulator and the anti-responder effects were seen with either whole serum or crude immunoglobulin preparations when one of these was added to the culture or used for pretreating cells before establishing the culture.