Characterization of a monoclonal antibody directed to a T cell suppressor factor.

A monoclonal antibody raised by fusion of immune BALB/c splenocytes with NS1 cells is described. BALB/c mice were immunized with a T suppressor factor (TsF) raised in DBA/2 mice with specificity for the P815 tumor. The TsF had been purified by affinity chromatography before its use as an immunogen. The monoclonal antibody (B16G) was shown to affect the course of P815 growth in DBA/2 mice if administered i.v. on days -2 to 0 before tumor cell inoculation. Mice treated with B16G demonstrated slower tumor development and growth than controls, and a small number of animals (about 10%) did not develop tumors; all controls did. It was also shown that B16G did not exhibit total specificity for the P815 tumor in that it had similar effects on the growth of an unrelated myosarcoma (M-1) of DBA/2 mice. The general immunopotentiating effect of the B16G monoclonal was demonstrated by the fact that spleen cells of DBA/2 mice that had received B16G showed significantly higher MLC than did equivalent controls. When spleen cells of DBA/2 mice were depleted of B16G-reactive cells by panning in vitro, it was also found that cells so treated gave rise to elevated MLC reactions in comparison to appropriate controls. When an immunoadsorbent was prepared with B16G and cell lysates from splenocytes of immunosuppressed mice were passed over it, the immunosuppressive properties of the lysate in MLC were eliminated. The conclusion that the B16G recognizes a marker common to a group of regulatory T cells in DBA/2 mice is discussed.