On the nature of blocking factors and their lymphoid target cells in an allogeneic tumor system

Employing the allogeneic tumor system of C3H mice transplanted with the L₁₂₁₀ leukemia, evidence was obtained that serum blocking activity can be due to antigen-antibody complexes. In this system, the cytotoxic activity induced in normal splenocytes by arming antibody is not modified by exposure to blocking sera. It is suggested that in allogeneic tumor systems, blockade can be due to antigen-antibody complexes and that blocking factors and arming antibodies act on different lymphoid populations.