Blocking of Lymphocyte-mediated Cytotoxicity for Rat Hepatoma Cells by Tumour-specific Antigen-Antibody Complexes

Abstract

LYMPHOCYTES from tumour-bearing animals are often cytotoxic in vitro against cultured tumour cells from the same individual1–4. It is possible that the serum of tumour-bearing hosts may contain circulating factors which interfere with the cell-mediated immune responses concerned in tumour rejection reactions5. Evidence has been provided by the demonstration that lymphocyte cytotoxicity against cultured tumour cells could be blocked by first exposing tumour cells to serum from tumour-bearing animals2,3; similar effects have also been observed in cancer patients6,7. The blocking factor in tumour-bearer serum has the characteristic properties of 7S immunoglobulins2, suggesting the involvement of tumour-specific antibody. Serum blocking activity is rapidly lost, however, in animals rendered tumour free and the activity of tumour-bearer serum can be neutralized by the addition of serum from these animals8,9. One explanation is that the blocking factor in tumour-bearer serum is antigen-antibody complex and the objective of these studies, using a transplanted rat hepatoma (D23), was to test directly whether such complexes prepared from solubilized tumour-specific antigen and antiserum exhibit blocking activity.