Radioiodination of rat hepatoma-specific antigens and retention of serological reactivity.

Papain-solubilized tumour-specific antigens from the aminoazo dye-induced rat hepatoma D23 were purified by a combination of lectin affinity and immunoadsorbent column chromatography. Isolated antigens were radio-iodinated using three procedures and analysed for their reaction with specific antibodies in syngeneic immune sera by double-antibody co-precipitation tests and by the rebinding of labelled antigens to specific and non-relevant antibodies immobilized on Sepharose-4B. Soluble hepatoma D23-specific antigens were labile to radiolabelling, and for optimal retention of serological reactivity it was necessary to protect the antigenic determinant by performing the chloramine T method of iodination with antigen bound to the immunoadsorbent followed by elution from the solid phase with 3M NaSCN. Immunoadsorption chromatography indicated that one consequence of radiolabelling hepatoma D23-specific antigen with 125I was a reduction in the affinity of the labelled antigen for its syngeneic specific antibody.