Summary.-Serum from rats bearing progressively growing aminoazo dye-induced rat hepatomata has been fractionated by Sephadex G150 gel filtration chromatography and isolated fractions have been examined by indirect membrane immunofluorescence techniques to detect tumour specific antigen and antibody. Hepatoma D23 -specific antigenic activity was associated with material (of approximate molecular weight <150,000) isolated in the included volume of the gel at pH 7-3. The fraction excluded from the gel (of approximate molecular weight > 150,000) was adjusted to pH 3-0 and further separated by Sephadex G150 gel filtration chromatography at pH 3*0 into gel included and excluded fractions. Hepatoma D23 specific antibody, demonstrable by membrane immunofluorescence staining of hepatoma D23 cells, was found to be eluted in the excluded volume and specific antigenic activity was retarded into the included volume of the gel. These results indicate that hepatoma D23 bearer serum contains free circulating tumour specific antigen in excess, together with specific immune complexes. The presence of these factors in tumour bearer serum is discussed in terms of " blocking " phenomena whereby serum factors may protect tumour cells from sensitized lymphocyte cytotoxic attack.

No abstract

Sera from rats bearing a progressively growing transplanted aminoazo-dye-induced hepatoma (hepatoma D23) have been examined for the presence of hepatoma D23-specfic 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 inbibitory 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.

No abstract