Development and inhibition of cytotoxic antibody against spontaneous murine breast cancer.

Increased cytolytic activity of mouse complement as a result of modified reaction conditions described permitted the detection of tumor-specific cytotoxic antibody in high dilutions of sera (1:100--1:000) from mice carrying spontaneously occuring autochthonous breast tumors, or primary syngeneic transplants of such tumors. However, these same sera failed to demonstrate cytotoxic antibody activity at low dilution (i.e., 1:10). Such a pattern of reactivity suggested the presence of an inhibitor of cytotoxic antibody in high concentrations of serum from tumor-bearing mice. Sequential measurements subsequent to primary tumor implantation revealed that, although the time of appearance of this inhibitor varied from tumor to tumor, it always became detectable simultaneously with significant levels of lymphocyte-blocking activity. Also like lymphocyte-blocking activity, the inhibitor of cytotoxic antibody disappeared following surgical tumor removal. In addition, the inhibitor of cytotoxic antibody activity was shown to operate through a competitive antigen-binding and blocking mechanism. This data suggests the possibility that a single serum moiety may be responsible for the efferent blocking of both the cellular and the humoral components of the immune tumor rejection response.