Detection of circulating hepatoma D23 antigen and immune complexes in tumour bearer serum

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.