Formed after Treatment

Summary: Recorded concentrations of the tumour-associated glycoprotein 72 (TAG-72) in ovarian cancer patients after repeated infusion of the antibody B72.3 were found to be falsely elevated when measured with an homologous immunometric assay involving the anti-TAG-72 antibody B72.3 (Test 1), or with an heterologous assay involving CC49 capture and B72.3 detector antibodies (Test 2). Test l yielded falsely elevated values up to l O4 kU/1. Test 2 gave slightly false positive elevations up to 102kU/l for only some of the samples with very high false-positive values in Test l. The interfering serum components bound to Protein G-Sepharose and could be precipitated with perchloric acid or by heating serum samples to 100 °C. Addition of non-specific murine immunoglobulins only partly suppressed false-positive values in both tests. Our results suggest that this interference is caused by human anti-B72.3 IgG indüced by B72.3 application, which to some extent specifically binds to determinants of the B72.3 antibody. Heat extraction of serum samples effectively eliminated interferences probably caused by anti-idiotypic antibodies, but did not affect real TAG-72