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Tumour‐specific antibody neutralization of factors in rat hepatoma‐bearer serum which abrogate lymph‐node‐cell cytotoxicity

Serum from hepatoma‐bearing rats has been shown to abrogate the cytotoxicity of immune lymph‐node cells when added to the target cells (blocking) or the effector cells (inhibition). Neutralization of these in vitro blocking and inhibitory reactions by sera containing antibody to tumour antigen has been demonstrated. Serum taken after hepatoma excision counteracted tumour‐bearer serum blocking only when the sera were mixed in equal proportions; syngeneic immune serum and a rabbit antiserum to hepatoma cells were shown to be more effective in neutralizing tumour‐bearer serum blocking activity. The syngeneic immune and rabbit antisera were also more effective than post‐excision serum in counteracting the inhibition of lymph‐node cell cytotoxicity by tumour‐bearer serum. The rabbit antiserum and syngeneic immune serum were found to block lymph‐node cell cytotoxicity at the level of the target cell, but these sera themselves did not inhibit lymph‐node cell cytotoxicity. These findings suggest that two distinct types of blocking at the target‐cell can occur: firstly, by sera containing high concentrations of antibody; and secondly, by sera containing immune complexes. The first type of blocking could be due to antibody masking of target‐cell antigens. The second type of blocking may involve interaction of the antigen part of the bound immune complex with receptors on the effector cell, so preventing their subsequent recognition of target cells.