Activation of human suppressor cells in mixed lymphocyte cultures

Lymphocytes transferred from 6-day-old human mixed lymphocyte cultures (MLC) inhibited the response to allogeneic cells of freshly taken lymphocytes autologous to the transferred MLC-responding cells. No specificity for this cell-dependent suppression could be determined. The inhibitory effects of the suppressing cells could be abrogated by moderate X-ray irradiation and significantly reduced by pretreating them with an anti-Ia-like antiserum and complement. The human suppressor cell responsible for the observed effects therefore appears to carry determinants equivalent to the murine Ia alloantigens.