Serum factors modifying cell mediated immunity to rat hepatoma D23 correlated with tumour growth

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Abstract
Sera from rats bearing a progressively growing transplanted aminoazo‐dye‐induced hepatoma (hepatoma D23) have been examined for the presence of hepatoma D23‐specific antigen, antibody and immune complexes throughout the course of tumour growth. The levels of these factors have been correlated with the in vitro blocking and inhibition of cytotoxic lymph‐node cells from immunized animals for cultured tumour cells. Sera from animals bearing small tumours (7–14 days after tumour implantation) contain free tumour‐specific antigen whilst immune complexes could not be detected. Although these sera were neither blocking nor inhibitory under the normal conditions of the test, when concentrated two and fourfold, inhibition but not blocking of lymph‐node cell cytotoxicity could be detected. In comparison sera from animals bearing large tumours (24–28 days) blocked but did no inhibit in vitro lymph‐node cell cytotoxicity and this correlates with the presence of tumour‐specific immune complexes in antibody excess. Animals with intermediate‐sized tumours had high levels of both blocking and inhibitory activity in the serum, these effects becoming apparent when neither free antibody nor free antigen could be detected. The relevance of these findings to the mechanism by which a growing tumour may escape specific cellular immune destruction is discussed.