The principal expression of immunity elicited in syngeneic rats immunized with rat hepatoma membrane fractions was the development of a tumour specific antibody response. This antibody was demonstrable by membrane immunofluorescence staining of viable hepatoma cells in suspension and the sera exhibited complement dependent cytotoxicity for cultured hepatoma cells. In the absence of complement, however, membrane immune sera were highly “blocking”, protecting plated hepatoma cells from attack by sensitized lymph node cells. The cell mediated immune response elicited by hepatoma membrane immunization was weak, as evaluated by the colony inhibitory activity of lymph node cells for hepatoma cells in vitro or the adoptive transfer of immunity with peritoneal exudate cells. Correlated with this overall pattern of immune response, membrane immunization did not elicit tumour rejection reactions. These findings are relevant to current views that humoral factors operate antagonistically to limit cell mediated immunity to tumours. A further relevant feature was the observation that membrane immunization, eliciting a prominent humoral immune reaction, conditioned the recipients so that they subsequently failed to elicit a tumour rejection immunity on treatment with irradiated tumour cells.
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