Primary humoral immune response against tumor membrane antigens and foreign antigens by plasma cell tumor bearer mice.

The MOPC-460 plasma cell tumor possesses tumor specific antigens. It nevertheless grows and kills its syngeneic host. The possible impairment of immune responsiveness in tumor bearing mice was investigated by measuring their ability to mount a humoral immune response against foreign antigens, such as sheep red blood cells or bacteriophage T4. No significant decrease in the response to either antigen was found until the tumor mass exceeded 10-15% of the host's body weight. Moreover, circulating anti-tumor antibodies were detected in the serum throughout the initial period of tumor growth. The possible interference of these antibodies with cell-mediated defence mechanism was ruled out by experiments where the humoral response was selectively suppressed from birth by repeated administrations of anti-immunoglobulin heavy chain antiserum. In a "suppressed" mice, tumors took, grew and developed more rapidly than in controls. It is concluded that, at least in the model studied, the humoral immune response operates as a defence mechanism against expansion of the tumor clone.