Abstract
Murine lymph node cells draining a local lymphoid cell allograft (LNd) exhibited weak cytolytic activity when tested immediately after surgical removal, However, upon mere in vitro cultivation, high cytotoxic activity developed. The in vitro generation of cytotoxic activity could be inhibited by treatment of the cells with mitomycin C. Upon transfer into a primary mixed lymphocyte culture, mitomycin C‐treated LNd cells effectively suppressed the induction of cytotoxic T lymphocytes (CTL). Using the velocity sedimentation technique at 1 × g the suppressor cells could be confined to the blast cells within LNd cells, the sensitized prekiller T cells being nonsuppressive. Results derived from independent experimental approaches suggested that the in vivo sensitized blast suppressor cells exhibited an immunological specific suppression, i.e. they selectively suppressed the in vitro induction of CTL reactive towards those H‐2 transplantation antigens against which the suppressor cells had been immunized. Thus, antigen‐specific suppressor cells (which were Thy‐1.2 positive) appeared to be specifically activated during the in vivo sensitization procedure.