Non-H-2 restriction specificity of tumor-regressor mouse sera with regard to their activity to inhibit tumor cell transplantation.

Inhibitory effect of serum from MM2-regressor C3H/He mice on transplantation of nonspecifically transplantable MM2 cells to mice of various strains was studied. The serum strongly inhibited transplantation of the cells to C3H/He and closely related CBA mice but only weakly inhibited the transplantation to Balb/c, DBA, DDD, B10D2, B10BR, B10A and B10AKM mice. By similar studies using sera from MM2-regressor B10D2 and B10BR mice, it was confirmed that this type of restriction specificity regarding the transplantation-inhibition activity of the serum between the regressor mice and the mice which received inoculation of MM2 cells pretreated with the regressor serum was not related to genes of H-2 region. Likewise, MM2-specific cell surface substance treated with MM2-regressor C3H/He serum induced resistance in C3H/He against transplantation of MM2 cells, but the resistance induced by the same treatment in Balb/c, DBA, DDD, B10BR, B10A and B10AKM was relatively weak. It was speculated that non-immunoglobin factors in regressor sera which play a major role in transplantation resistance and their binding sites on unidentified cells which cooperate with the factors have allotypes, and that compatibility of the allotype was necessary for binding of the factor to the site. It was also found that regressor serum contained factors which enhanced cytolytic reactions in vitro by culture-induced nonspecifically cytotoxic cells or by stimulated macrophages in a nonrestricted manner. These factors may be responsible for the looseness of the restriction specificity of the in vivo reactions.