Inhibition of mixed leukocyte culture by anti-idiotypic antibodies.

(CBA x C57BL/6)F1 antisera prepared by injecting F1 mice with CBA T lymphocytes or CBA anti-C57BL/6 alloantibodies were tested for their ability to inhibit the mixed leukocyte culture (MLC) response. Presence of antiserum throughout the culture period in the absence of complement did not have any effect on the MLC response. Treatment of CBA responder cells with F1 antiserum and complement prior to the culture specifically inhibited the MLC response. Specificity of the suppression was ascertained; absorption of the F1 sera with F1 or C57BL/6 spleen cells did not remove the suppressive factor, whereas absorption with CBA spleen cells did so. F1 antiserum treatment left intact the response to third party alloantigens (DBA/2). Immunabsorbent columns with alloantibody of corresponding specificity removed the suppressive factor from anti-T cell sera as well as from antisera to alloantibody. The data suggest that the circulating alloantibody population contains molecules which share idiotypic determinants with surface receptors on T cells recognizing the same alloantigens.