Generation of suppressor cells in mice immunized with M locus-incompatible lymphocytes.

Alloimmunization of mice with M locus-incompatible lymphocytes resulted in the generation of suppressor cells in the immunized host. Lymph node cells from such alloimmunized mice suppressed the in vitro cytotoxic response of normal cells to H-2 alloantigens. The suppression generated was greater than could be accounted for by dilution of the prekiller cell population with cells possibly devoid of cytotoxic potential from M locus preimmunized mice. Using M locus pseudocongenic mice, the suppressive effect was shown to be largely attributable to M locus determinants; restimulation of suppressor cells in culture with the specific M locus was required for suppression of effector cell generation. The in vivo effect of suppressor cells was tested in a graft-versus-host reaction; injection of M locus preimmunized cells into footpads of F1 hybrid mice suppressed the popliteal lymph node enlargement compared with lymph node size after injection of control preimmunized cells. Although the suppressive effect is mainly attributable to M locus determinants, incompatibility for the DBA/2 antigen may add to the suppression. The study of inhibitory effects on T cell cytotoxicity because of serologically undetectable lymphocyte-activating determinants (Mls) could lead to the better understanding of suppressive mechanisms which may allow the growth of syngeneic tumours.