Immunoradiometric assay for quantitative determination of cancer antigen 15-3(CA15-3) in human serum or plasma
The MUC-1 antigen is a membrane-anchored mucin-type glycoprotein present in malignant and epithelial cells of certain organs, e.g. breast, lung, ovary and pancreas. The apo-protein of the MUC-1 mucin contains a transmembrane domain, a cytoplasmic domain, and an extracellular carbohydrate rich domain. The extracellular domain is characterized by polymorphism with respect to the member of a 20 amino acid tandem repeat (VNTR polymorphism). The MUC-1 breast cancer mucin (CA15-3 antigen) is secreted from tumor cells and can be used as a serological marker of breast cancer.
The assay is a one-step non-competitive immunoradiometric assay (IRMA) method (sandwich principle). The present method employs several monoclonal anti-CA15-3 antibodies which recognize two different epitopes of the molecules. One antibody is absorbed in solid phase (coated tube), the others (labeled with Iodine-125, labeled with biotin) are used as tracer and tracer buffer. The sample to be tested, is incubated in the coated tube, following the incubation, after aspiration and washing, the labeled antibody is added to the coated tubes, where it binds to the solid phase, by means of the antigen in standards and samples. The amount of bound tracer will thus be directly proportional to the antigen concentration. After a further aspiration and washing cycle, the residual radioactivity in the tubes is measured in a gamma counter.