AN ENZYME-IMMUNOASSAY FOR CARCINOEMBRYONIC ANTIGEN (CEA) WITH HOMOGENEOUS REACTIVITY TO DIFFERENT CEA PREPARATIONS AND LOW CROSS-REACTIVITYWITH CEA-RELATED NORMAL ANTIGENS

A new sandwich-type solid-phase enzyme immunoassay (EIA) for carcinoem bryonic antigen (CEA) was established by using two selected monoclonal antibodies (MAbs). One MAb, F82-61, which is immobilized on polystyre ne beads, reacts with an epitope present on the N-terminal domain (N) of the CEA molecule and the other, F11-39, which is conjugated to hors eradish peroxidase (HRP), recognizes an epitope present on the C-termi nal domain (B3) of the CEA molecule. The assay consists of incubating 0.05 ml of test serum both with F82-61-coated beads and HRP-labeled F1 1-39 at room temperature for 2 h. The assay system, referred to as New EIA, showed very homogeneous reactivity with purified CEA preparation s from different tumors and could discriminate CEA from four CEA-relat ed normal antigens tested; nonspecific cross-reacting antigen (NCA), N CA-2, normal fecal antigen-1 (NFA-1) and NFA-2. The assessment of tech nical qualities, such as reproducibility, recovery and dilution tests, demonstrated the excellent performance of New EIA. Serum samples (n = 604) from patients with malignant or non-malignant disease, as well a s from healthy individuals, were analyzed by New EIA and by two commer cial CEA immunoassays which both showed heterogeneous reactivity with different CEA preparations and reacted to a greater or lesser extent w ith NCA-2 and NFA-2, and it was found that New EIA significantly incre ased the sensitivity and specificity of tumor diagnosis as compared wi th the commercial assays.