Immunological similarity of CEA with α1-acid glycoprotein (orosomucoid)

The authors have demonstrated that 125I-CEA (carcinoembryonic antigen) from two commerical sources (Roche and CIS RIA kit) can be precipitated by antibody to α1-acid glycoprotein (AG) dose-dependently. The binding of 125I-CEA to anti-AG can be displaced by unlabelled AG, though, there was no cross-reaction between AG and anti-CEA. The data strongly suggest that CEA has an immunological similarity to AG. The perchloric acid extract from cancerous tissue was fractionated on a Sephadex G-200 column, and the first eluted fraction (containing large amounts of CEA) was subjected to affinity chromatography using anti-AG bound to Sepharose. The bound fraction was eluted, labelled with 125I, and then applied to a Sephadex G-200 column with carrier protein. The radioactivity was found mainly in the large molecular size eluted fraction (Fr 1). Almost all radioactivity of Fr 1 was precipitated by anti-AG and anti-CEA. This experiment also demonstrated that a large molecular weight component (Msub(r) 180000) obtained from tumour was immunologically related to both CEA and AG. Based on differences in binding affinities between CEA with anti-CEA and with anti-AG the authors postulate that CEA may be a large molecular precursor of AG (big form of AG). (Auth.)